LHS

LHS ia a Rails-Gem, providing an ActiveRecord like interface to access HTTP-JSON-Services from Rails Applications. Special features provided by this gem are: Multiple endpoint configuration per resource, active-record-like query-chains, scopes, error handling, relations, request cycle cache, batch processing, including linked resources (hypermedia), data maps (data accessing), nested-resource handling, ActiveModel like backend validation conversion, formbuilder-compatible, three types of pagination support, service configuration per resource, kaminari-support and much more.

LHS uses LHC for advanced http requests.

gem 'lhs'

# config/initializers/lhc.rb

LHC.configure do |config|
  config.placeholder(:service, 'https://my.service.dev')
end

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/records/{id}'

end

# app/controllers/application_controller.rb

record = Record.find_by(email: 'somebody@mail.com')
record.review # "Lunch was great

• LHS
• Quickstart
• Installation/Startup checklist
• Record
  • Endpoints
    • Configure endpoint hosts
    • Endpoint Priorities
  • Provider
  • Record inheritance
  • Find multiple records
    • fetch
    • where
    • Reuse/Dry where statements: Use scopes
    • all
    • all with unpaginated endpoints
    • Retrieve the amount of a collection of items: count vs. length
  • Find single records
    • find
    • find_by
    • first
    • last
  • Work with retrieved data
    • Automatic detection/conversion of collections
    • Map complex data for easy access
    • Access and identify nested records
      • Relations / Associations
        • has_many
        • has_one
    • Unwrap nested items from the response body
    • Determine collections from the response body
    • Load additional data based on retrieved data
  • Chain complex queries
    • Chain where queries
    • Expand plain collections of links: expanded
    • Error handling with chains
    • Resolve chains: fetch
    • Add request options to a query chain: options
    • Control pagination within a query chain
  • Record pagination
    • Pagination strategy
      • Pagination strategy: offset (default)
      • Pagination strategy: page
      • Pagination strategy: start
      • Pagination strategy: link
    • Pagination keys
      • limit_key
      • pagination_key
      • total_key
    • Pagination links
      • next?
      • previous?
    • Kaminari support (limited)
  • Build, create and update records
    • Create new records
      • create
        • Unwrap nested data when creation response nests created record data
        • Create records through associations: Nested sub resources
    • Start building new records
    • Change/Update existing records
      • save
      • update
        • Directly via Record
        • per Instance
      • partial_update
    • Endpoint url parameter injection during record creation/change
    • Record validation
      • Configure record validations
      • HTTP Status Codes for validation errors
      • Reset validation errors
      • Add validation errors
      • Validation errors for nested data
      • Translation of validation errors
      • Validation error types: errors vs. warnings
        • Persistance failed: errors
        • Persistance succeeded: warnings
      • Using ActiveModel::Validations none the less
    • Use form_helper to create and update records
  • Destroy records
  • Record getters and setters
    • Record setters
    • Record getters
  • Include linked resources (hyperlinks and hypermedia)
    • Generate links from parameters
    • Ensure the whole linked collection is included with includes
    • Include only the first linked page of a linked collection: includes_first_page
    • Include various levels of linked data
    • Identify and cast known records when including records
    • Apply options for requests performed to fetch included records
    • compact: Remove included resources that didn't return any records
  • Record batch processing
    • all
      • Using all, when endpoint does not implement response pagination meta data
    • find_each
    • find_in_batches
  • Convert/Cast specific record types: becomes
  • Assign attributes
• Request Cycle Cache
  • Change store for LHS' request cycle cache
  • Disable request cycle cache
• Automatic Authentication (OAuth)
  • Configure multiple auth providers (even per endpoint)
  • Configure providers
• Option Blocks
• Request tracing
• Extended Rollbar Logging
• Testing with LHS
  • Test helper
    • Stub
      • stub_all
  • Test query chains
    • By explicitly resolving the chain: fetch
    • Without resolving the chain: where_values_hash
• Extended developer documentation
  • Accessing data in LHS
• License

• Install LHS gem, preferably via Gemfile
• Configure LHC via an config/initializers/lhc.rb (See: https://github.com/local-ch/lhc#configuration)
• Add LHC::Caching to LHC.config.interceptors to facilitate LHS' Request Cycle Cache
• Store all LHS::Records in app/models for autoload/preload reasons
• Request data from services via LHS from within your rails controllers

Endpoint, the entry point to a service, a process, a queue or a topic in a service-oriented architecture

Start a record with configuring one or multiple endpoints.

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/records/{id}'
  endpoint '{+service}/accociation/{accociation_id}/records'
  endpoint '{+service}/accociation/{accociation_id}/records/{id}'

end

You can also add request options to be used with configured endpoints:

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+service}/records', auth: { bearer: -> { access_token } }
  endpoint '{+service}/records/{id}', auth: { bearer: -> { access_token } }

end

-> Check LHC for more information about request options

It's common practice to use different hosts accross different environments in a service-oriented architecture.

Use LHC placeholders to configure different hosts per environment:

# config/initializers/lhc.rb

LHC.configure do |config|
  config.placeholder(:search, ENV['SEARCH'])
end

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+search}/api/search.json'

end

DON'T!

Please DO NOT mix host placeholders with and endpoint's resource path, as otherwise LHS will not work properly.

# config/initializers/lhc.rb

LHC.configure do |config|
  config.placeholder(:search, 'http://tel.search.ch/api/search.json')
end

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+search}'
  
end

LHS uses endpoint configurations to determine what endpoint to use when data is requested, in a similar way, routes are identified in Rails to map requests to controllers.

If they are ambiguous, LHS will always use the first one found:

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/bananas'

end

# app/controllers/some_controller.rb

Record.fetch

GET https://service.example.com/records

Be aware that, if you configure ambiguous endpoints across multiple classes, the order of things is not deterministic. Ambiguous endpoints across multiple classes need to be avoided.

Providers in LHS allow you to group shared endpoint options under a common provider.

# app/models/provider/base_record.rb

module Provider
  class BaseRecord < LHS::Record
    provider params: { api_key: 123 }
  end
end

Now every record, part of that particular provider can inherit the provider's BaseRecord.

# app/models/provider/account.rb

module Provider
  class Account < BaseRecord
    endpoint '{+host}/records'
    endpoint '{+host}/records/{id}'
  end
end

# app/controllers/some_controller.rb

Provider::Account.find(1)

GET https://provider/records/1?api_key=123

And requests made via those provider records apply the common provider options.

You can inherit from previously defined records and also inherit endpoints that way:

# app/models/base.rb

class Base < LHS::Record
  endpoint '{+service}/records/{id}'
end

# app/models/record.rb

class Record < Base
end

# app/controllers/some_controller.rb

Record.find(1)

GET https://service.example.com/records/1

In case you want to just fetch the records endpoint, without applying any further queries or want to handle pagination, you can simply call fetch:

# app/controllers/some_controller.rb

records = Record.fetch

  GET https://service.example.com/records

You can query a service for records by using where:

# app/controllers/some_controller.rb

Record.where(color: 'blue')

  GET https://service.example.com/records?color=blue

If the provided parameter – color: 'blue' in this case – is not part of the endpoint path, it will be added as query parameter.

# app/controllers/some_controller.rb

Record.where(accociation_id: '12345')

GET https://service.example.com/accociation/12345/records

If the provided parameter – accociation_id in this case – is part of the endpoint path, it will be injected into the path.

You can also provide hrefs to fetch multiple records:

# app/controllers/some_controller.rb

Record.where('https://service.example.com/accociation/12345/records')

GET https://service.example.com/accociation/12345/records

In order to reuse/dry where statements organize them in scopes:

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/records/{id}'

  scope :blue, -> { where(color: 'blue') }
  scope :available, ->(state) { where(available: state) }

end

# app/controllers/some_controller.rb

records = Record.blue.available(true)

GET https://service.example.com/records?color=blue&available=true

You can fetch all remote records by using all. Pagination will be performed automatically (See: Record pagination)

# app/controllers/some_controller.rb

records = Record.all

  GET https://service.example.com/records?limit=100
  GET https://service.example.com/records?limit=100&offset=100
  GET https://service.example.com/records?limit=100&offset=200

# app/controllers/some_controller.rb

records.size # 300

In case your record endpoints are not implementing any pagination, configure it to be paginated: false. Pagination will not be performed automatically in those cases:

# app/models/record.rb

class Record < LHS::Record
  configuration paginated: false
end

# app/controllers/some_controller.rb

records = Record.all

  GET https://service.example.com/records

The different behavior of count and length is based on ActiveRecord's behavior.

count The total number of items available remotly via the provided endpoint/api, communicated via pagination meta data.

length The number of items already loaded from the endpoint/api and kept in memory right now. In case of a paginated endpoint this can differ to what count returns, as it depends on how many pages have been loaded already.

find finds a unique record by unique identifier (usually id or href). If no record is found an error is raised.

Record.find(123)

GET https://service.example.com/records/123

Record.find('https://anotherservice.example.com/records/123')

GET https://anotherservice.example.com/records/123

find can also be used to find a single unique record with parameters:

Record.find(another_identifier: 456)

GET https://service.example.com/records?another_identifier=456

You can also fetch multiple records by id in parallel:

Record.find(1, 2, 3)

# In parallel:
  GET https://service.example.com/records/1
  GET https://service.example.com/records/2
  GET https://service.example.com/records/3

find_by finds the first record matching the specified conditions. If no record is found, nil is returned.

find_by! raises LHC::NotFound if nothing was found.

Record.find_by(color: 'blue')

GET https://service.example.com/records?color=blue

first is an alias for finding the first record without parameters. If no record is found, nil is returned.

first! raises LHC::NotFound if nothing was found.

Record.first

GET https://service.example.com/records?limit=1

first can also be used with options:

Record.first(params: { color: :blue })

GET https://service.example.com/records?color=blue&limit=1

last is an alias for finding the last record without parameters. If no record is found, nil is returned.

last! raises LHC::NotFound if nothing was found.

Record.last

last can also be used with options:

Record.last(params: { color: :blue })

After fetching single or multiple records you can navigate the received data with ease:

records = Record.where(color: 'blue')
records.length # 4
records.count # 400
record = records.first
record.type # 'Business'
record[:type] # 'Business'
record['type'] # 'Business'

How to configure endpoints for automatic collection detection?

LHS detects automatically if the responded data is a single business object or a set of business objects (collection).

Conventionally, when the respons contains an items key { items: [] } it's treated as a collection, but also if the respons contains a plain raw array: [{ href: '' }] it's also treated as a collection.

If you need to configure the attribute of the response providing the collection, configure items_key as explained here: Determine collections from the response body

To influence how data is accessed, simply create methods inside your Record to access complex data structures:

# app/models/record.rb

class Record < LHS::Record

  endpoint '{+service}/records'

  def name
    dig(:addresses, :first, :business, :identities, :first, :name)
  end
end

Nested records, in nested data, are automatically casted to the correct Record class, when they provide an href and that href matches any defined endpoint of any defined Record:

# app/models/place.rb

class Place < LHS::Record
  endpoint '{+service}/places'
  endpoint '{+service}/places/{id}'

  def name
    dig(:addresses, :first, :business, :identities, :first, :name)
  end
end

# app/models/favorite.rb

class Favorite < LHS::Record
  endpoint '{+service}/favorites'
  endpoint '{+service}/favorites/{id}'
end

# app/controllers/some_controller.rb

favorite = Favorite.includes(:place).find(123)
favorite.place.name # local.ch AG

GET https://service.example.com/favorites/123

{... place: { href: 'https://service.example.com/places/456' }}

GET https://service.example.com/places/456

If automatic detection of nested records does not work, make sure your Records are stored in app/models! See: Insallation/Startup checklist

Typically nested data is automatically casted when accessed (See: Access and identify nested records), but sometimes API's don't provide dedicated endpoints to retrieve these records. In those cases, those records are only available through other records and don't have an href on their own and can't be casted automatically, when accessed.

To be able to implement Record-specific logic for those nested records, you can define relations/associations.

# app/models/location.rb

class Location < LHS::Record

  endpoint '{+service}/locations/{id}'

  has_many :listings

end

# app/models/listing.rb

class Listing < LHS::Record

  def supported?
    type == 'SUPPORTED'
  end
end

# app/controllers/some_controller.rb

Location.find(1).listings.first.supported? # true

GET https://service.example.com/locations/1
{... listings: [{ type: 'SUPPORTED' }] }

class_name: Specify the class name of the relation. Use it only if that name can't be inferred from the relation name. So has_many :photos will by default be linked to the Photo class, but if the real class name is e.g. CustomPhoto or namespaced Custom::Photo, you'll have to specify it with this option.

# app/models/custom/location.rb

module Custom
  class Location < LHS::Record
    endpoint '{+service}/locations'
    endpoint '{+service}/locations/{id}'
    
    has_many :photos, class_name: 'Custom::Photo'
  end
end

# app/models/custom/photo.rb

module Custom
  class Photo < LHS::Record
  end
end

# app/models/transaction.rb

class Transaction < LHS::Record

  endpoint '{+service}/transaction/{id}'

  has_one :user
end

# app/models/user.rb

class User < LHS::Record

  def email
    self[:email_address]
  end
end

# app/controllers/some_controller.rb

Transaction.find(1).user.email_address # steve@local.ch

GET https://service.example.com/transaction/1
{... user: { email_address: 'steve@local.ch' } }

class_name: Specify the class name of the relation. Use it only if that name can't be inferred from the relation name. So has_many :photos will by default be linked to the Photo class, but if the real class name is e.g. CustomPhoto or namespaced Custom::Photo, you'll have to specify it with this option.

# app/models/custom/location.rb

module Custom
  class Location < LHS::Record
    endpoint '{+service}/locations'
    endpoint '{+service}/locations/{id}'
    
    has_one :photo, class_name: 'Custom::Photo'
  end
end

# app/models/custom/photo.rb

module Custom
  class Photo < LHS::Record
  end
end

If the actual item data is mixed with metadata in the response body, LHS allows you to configure a record in a way to automatically unwrap items from within nested response data.

item_key is used to unwrap the actual object from within the response body.

# app/models/location.rb

class Location < LHS::Record
  configuration item_key: [:response, :location]
end

# app/controllers/some_controller.rb

location = Location.find(123)
location.id # 123

GET https://service.example.com/locations/123
{... response: { location: { id: 123 } } }

items_key key used to determine the collection of items of the current page (e.g. docs, items, etc.), defaults to 'items':

# app/models/search.rb

class Search < LHS::Record
  configuration items_key: :docs
end

# app/controllers/some_controller.rb

search_result = Search.where(q: 'Starbucks')
search_result.first.address # Bahnhofstrasse 5, 8000 Zürich

GET https://service.example.com/search?q=Starbucks
{... docs: [... {...  address: 'Bahnhofstrasse 5, 8000 Zürich' }] }

In order to load linked data from already retrieved data, you can use load! (or reload!).

# app/controllers/some_controller.rb

record = Record.find(1)
record.associated_thing.load!

GET https://things/4
{ name: "Steve" }

# app/controllers/some_controller.rb
record.associated_thing.name # Steve

record.associated_thing.load! # Does NOT create another request, as it is already loaded
record.associated_thing.reload! # Does request the data again from remote

GET https://things/4
{ name: "Steve" }

Method chaining, also known as named parameter idiom, is a common syntax for invoking multiple method calls in object-oriented programming languages. Each method returns an object, allowing the calls to be chained together without requiring variables to store the intermediate results

In order to simplify and enhance preparing complex queries for performing single or multiple requests, LHS implements query chains to find single or multiple records.

LHS query chains do lazy evaluation to only perform as many requests as needed, when the data to be retrieved is actually needed.

Any method, accessing the content of the data to be retrieved, is resolving the chain in place – like .each, .first, .some_attribute_name. Nevertheless, if you just want to resolve the chain in place, and nothing else, fetch should be the method of your choice:

# app/controllers/some_controller.rb

Record.where(color: 'blue').fetch

# app/controllers/some_controller.rb

records = Record.where(color: 'blue')
[...]
records.where(available: true).each do |record|
  [...]
end

  GET https://service.example.com/records?color=blue&available=true

In case you wan't to check/debug the current values for where in the chain, you can use where_values_hash:

records.where_values_hash

# {color: 'blue', available: true}

Some endpoints could respond only with a plain list of links and without any expanded data, like search results.

Use expanded to have LHS expand that data, by performing necessary requests in parallel:

# app/controllers/some_controller.rb

Search.where(what: 'Cafe').expanded

GET https://service.example.com/search?what=Cafe
{...
  "items" : [
    {"href": "https://service.example.com/records/1"},
    {"href": "https://service.example.com/records/2"},
    {"href": "https://service.example.com/records/3"}
  ]
}

In parallel:
  > GET https://service.example.com/records/1
  < {... name: 'Cafe Einstein'}
  > GET https://service.example.com/records/2
  < {... name: 'Starbucks'}
  > GET https://service.example.com/records/3
  < {... name: 'Plaza Cafe'}

{
  ...
  "items" : [
    {
      "href": "https://service.example.com/records/1",
      "name": 'Cafe Einstein',
      ...
    },
    {
      "href": "https://service.example.com/records/2",
      "name": 'Starbucks',
      ...
    },
    {
      "href": "https://service.example.com/records/3",
      "name": 'Plaza Cafe',
      ...
    }
  ]
}

You can also apply request options to expanded. Those options will be used to perform the additional requests to expand the data:

# app/controllers/some_controller.rb

Search.where(what: 'Cafe').expanded(auth: { bearer: access_token })

One benefit of chains is lazy evaluation. But that also means they only get resolved when data is accessed. This makes it hard to catch errors with normal rescue blocks:

# app/controllers/some_controller.rb

def show
  @records = Record.where(color: blue) # returns a chain, nothing is resolved, no http requests are performed
rescue => e
  # never ending up here, because the http requests are actually performed in the view, when the query chain is resolved
end

# app/views/some/view.haml

= @records.each do |record| # .each resolves the query chain, leads to http requests beeing performed, which might raises an exception
  = record.name

To simplify error handling with chains, you can also chain error handlers to be resolved, as part of the chain.

If you need to render some different view in Rails based on an LHS error raised during rendering the view, please proceed as following:

# app/controllers/some_controller.rb

def show
  @records = Record
    .rescue(LHC::Error, ->(error){ rescue_from(error) })
    .where(color: 'blue')
  render 'show'
  render_error if @error
end

private

def rescue_from(error)
  @error = error
  nil
end

def render_error
  self.response_body = nil # required to not raise AbstractController::DoubleRenderError
  render 'error'
end

> GET https://service.example.com/records?color=blue
< 406

In case no matching error handler is found the error gets re-raised.

-> Read more about LHC error types/classes

If you want to inject values for the failing records, that might not have been found, you can inject values for them with error handlers:

# app/controllers/some_controller.rb

data = Record
  .rescue(LHC::Unauthorized, ->(response) { Record.new(name: 'unknown') })
  .find(1, 2, 3)

data[1].name # 'unknown'

In parallel:
  > GET https://service.example.com/records/1
  < 200
  > GET https://service.example.com/records/2
  < 400
  > GET https://service.example.com/records/3
  < 200

-> Read more about LHC error types/classes

If an error handler returns nil an empty LHS::Record is returned, not nil!

In case you want to ignore errors and continue working with nil in those cases, please use ignore:

# app/controllers/some_controller.rb

record = Record.ignore(LHC::NotFound).find_by(color: 'blue')

record # nil

In case you need to resolve a query chain in place, use fetch:

# app/controllers/some_controller.rb

records = Record.where(color: 'blue').fetch

You can apply options to the request chain. Those options will be forwarded to the request performed by the chain/query:

# app/controllers/some_controller.rb

options = { auth: { bearer: '123456' } } # authenticated with OAuth token

# app/controllers/some_controller.rb

AuthenticatedRecord = Record.options(options)

# app/controllers/some_controller.rb

blue_records = AuthenticatedRecord.where(color: 'blue')

GET https://service.example.com/records?color=blue { headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

AuthenticatedRecord.create(color: 'red')

POST https://service.example.com/records { body: '{ color: "red" }' }, headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

record = AuthenticatedRecord.find(123)

GET https://service.example.com/records/123 { headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record = record.options(options) # starting a new chain based on the found record

# app/controllers/some_controller.rb

authenticated_record.valid?

POST https://service.example.com/records/validate { body: '{...}', headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record.save

POST https://service.example.com/records { body: '{...}', headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record.destroy

DELETE https://service.example.com/records/123 { headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record.update(name: 'Steve')

POST https://service.example.com/records/123 { body: '{...}', headers: { 'Authentication': 'Bearer 123456' } }

page sets the page that you want to request.

per sets the amount of items requested per page.

limit is an alias for per. But without providing arguments, it resolves the query and provides the current response limit per page

# app/controllers/some_controller.rb

Record.page(3).per(20).where(color: 'blue')

GET https://service.example.com/records?offset=40&limit=20&color=blue

# app/controllers/some_controller.rb

Record.page(3).per(20).where(color: 'blue')

GET https://service.example.com/records?offset=40&limit=20&color=blue

The applied pagination strategy depends on what's configured for the particular record: See Record pagination

You can configure pagination on a per record base. LHS differentiates between the pagination strategy (how items/pages are navigated and calculated) and pagination keys (how stuff is named and accessed).

The offset pagination strategy is LHS's default pagination strategy, so nothing needs to be (re-)configured.

The offset pagination strategy starts with 0 and offsets by the amount of items, thay you've already recived – typically limit.

# app/models/record.rb

class Search < LHS::Record
  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  offset: 0
}
In parallel:
  GET https://service.example.com/records?limit=100&offset=100
  GET https://service.example.com/records?limit=100&offset=200

In comparison to the offset strategy, the page strategy just increases by 1 (page) and sends the next batch of items for the next page.

# app/models/record.rb

class Search < LHS::Record
  configuration pagination_strategy: 'page', pagination_key: 'page'

  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  page: 1
}
In parallel:
  GET https://service.example.com/records?limit=100&page=2
  GET https://service.example.com/records?limit=100&page=3

In comparison to the offset strategy, the start strategy indicates with which item the current page starts. Typically it starts with 1 and if you get 100 items per page, the next start is 101.

# app/models/record.rb

class Search < LHS::Record
  configuration pagination_strategy: 'start', pagination_key: 'startAt'

  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  page: 1
}
In parallel:
  GET https://service.example.com/records?limit=100&startAt=101
  GET https://service.example.com/records?limit=100&startAt=201

The link strategy continuously follows in-response embedded links to following pages until the last page is reached (indicated by no more next link).

WARNING

Loading all pages from a resource paginated with links only can result in very poor performance, as pages can only be loaded sequentially!

# app/models/record.rb

class Search < LHS::Record
  configuration pagination_strategy: 'link'

  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  limit: 100,
  next: {
    href: 'https://service.example.com/records?from_record_id=p62qM5p0NK_qryO52Ze-eg&limit=100'
  }
}
Sequentially:
  GET https://service.example.com/records?from_record_id=p62qM5p0NK_qryO52Ze-eg&limit=100
  GET https://service.example.com/records?from_record_id=xcaoXBmuMyFFEcFDSgNgDQ&limit=100

limit_key sets the key used to indicate how many items you want to retrieve per page e.g. size, limit, etc. In case the limit_key parameter differs for how it needs to be requested from how it's provided in the response, use body and parameter subkeys.

# app/models/record.rb

class Record < LHS::Record
  configuration limit_key: { body: [:pagination, :max], parameter: :max }

  endpoint '{+service}/records'
end

# app/controllers/some_controller.rb

records = Record.where(color: 'blue')
records.limit # 20

GET https://service.example.com/records?color=blue&max=100
{ ...
  items: [...],
  pagination: { max: 20 }
}

pagination_key defines which key to use to paginate a page (e.g. offset, page, startAt etc.). In case the limit_key parameter differs for how it needs to be requested from how it's provided in the response, use body and parameter subkeys.

# app/models/record.rb

class Record < LHS::Record
  configuration pagination_key: { body: [:pagination, :page], parameter: :page }, pagination_strategy: :page

  endpoint '{+service}/records'
end

# app/controllers/some_controller.rb

records = Record.where(color: 'blue').all
records.length # 300

GET https://service.example.com/records?color=blue&limit=100
{... pagination: { page: 1 } }
In parallel:
  GET https://service.example.com/records?color=blue&limit=100&page=2
  {... pagination: { page: 2 } }
  GET https://service.example.com/records?color=blue&limit=100&page=3
  {... pagination: { page: 3 } }

total_key defines which key to user for pagination to describe the total amount of remote items (e.g. total, totalResults, etc.).

# app/models/record.rb

class Record < LHS::Record
  configuration total_key: [:pagination, :total]

  endpoint '{+service}/records'
end

# app/controllers/some_controller.rb

records = Record.where(color: 'blue').fetch
records.length # 100
records.count # 300

GET https://service.example.com/records?color=blue&limit=100
{... pagination: { total: 300 } }

next? Tells you if there is a next link or not.

# app/controllers/some_controller.rb

@records = Record.where(color: 'blue').fetch

GET https://service.example.com/records?color=blue&limit=100
{... items: [...], next: 'https://service.example.com/records?color=blue&limit=100&offset=100' }

# app/views/some_view.haml

- if @records.next?
  = render partial: 'next_arrow'

previous? Tells you if there is a previous link or not.

# app/controllers/some_controller.rb

@records = Record.where(color: 'blue').fetch

GET https://service.example.com/records?color=blue&limit=100
{... items: [...], previous: 'https://service.example.com/records?color=blue&limit=100&offset=100' }

# app/views/some_view.haml

- if @records.previous?
  = render partial: 'previous_arrow'

LHS implements an interface that makes it partially working with Kaminari.

The kaminari’s page parameter is in params[:page]. For example, you can use kaminari to render paginations based on LHS Records. Typically, your code will look like this:

# controller
@items = Record.page(params[:page]).per(100)

# view
= paginate @items

create will return the object in memory if persisting fails, providing validation errors in .errors (See record validation).

create! instead will raise an exception.

create always builds the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is build.

# app/controllers/some_controller.rb

record = Record.create(
  text: 'Hello world'
)

POST https://service.example.com/records { body: "{ 'text' : 'Hello world' }" }

-> See record validation for how to handle validation errors when creating records.

item_created_key key used to merge record data thats nested in the creation response body:

# app/models/location.rb

class Location < LHS::Record

  configuration item_created_key: [:response, :location]

end

# app/controllers/some_controller.rb

location.create(lat: '47.3920152', long: '8.5127981')
location.address # Förrlibuckstrasse 62, 8005 Zürich

POST https://service.example.com/locations { body: "{ 'lat': '47.3920152', long: '8.5127981' }" }
{... { response: { location: {... address: 'Förrlibuckstrasse 62, 8005 Zürich' } } } } 

# app/models/restaurant.rb

class Restaurant < LHS::Record
  endpoint '{+service}/restaurants/{id}'
end

# app/models/feedback.rb

class Feedback < LHS::Record
  endpoint '{+service}/restaurants/{restaurant_id}/feedbacks'
end

# app/controllers/some_controller.rb

restaurant = Restaurant.find(1)

GET https://service.example.com/restaurants/1
{... reviews: { href: 'https://service.example.com/restaurants/1/reviews' }}

# app/controllers/some_controller.rb

restaurant.reviews.create(
  text: 'Simply awesome!'
)

POST https://service.example.com/restaurants/1/reviews { body: "{ 'text': 'Simply awesome!' }" }

With new or build you can start building new records from scratch, which can be persisted with save:

# app/controllers/some_controller.rb

record = Record.new # or Record.build
record.name = 'Starbucks'
record.save

POST https://service.example.com/records { body: "{ 'name' : 'Starbucks' }" }

save persist the whole object in its current state.

save will return false if persisting fails. save! instead will raise an exception.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Starbucks', recommended: null }

# app/controllers/some_controller.rb

record.recommended = true
record.save

POST https://service.example.com/records/1z-5r1fkaj { body: "{ 'name': 'Starbucks', 'recommended': true }" }

-> See record validation for how to handle validation errors when updating records.

# app/controllers/some_controller.rb

Record.update(id: '1z-5r1fkaj', name: 'Steve')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Steve' }

update persists the whole object after new parameters are applied through arguments.

update will return false if persisting fails. update! instead will raise an exception.

update always updates the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is updated.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Starbucks', recommended: null }

# app/controllers/some_controller.rb

record.update(recommended: true)

POST https://service.example.com/records/1z-5r1fkaj { body: "{ 'name': 'Starbucks', 'recommended': true }" }

-> See record validation for how to handle validation errors when updating records.

You can use update and the end of query-chains:

# app/controllers/some_controller.rb

record.options(method: :put).update(recommended: true)

You can also pass explicit request options to update, by passing two explicit hashes:

# app/controllers/some_controller.rb

record.update({ recommended: true }, { method: 'put' })

partial_update updates just the provided parameters.

partial_update will return false if persisting fails. partial_update! instead will raise an exception.

partial_update always updates the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is updated.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Starbucks', recommended: null }

# app/controllers/some_controller.rb

record.partial_update(recommended: true)

POST https://service.example.com/records/1z-5r1fkaj { body: "{ 'recommended': true }" }

-> See record validation for how to handle validation errors when updating records.

You can use partial_update at the end of query-chains:

# app/controllers/some_controller.rb

record.options(method: :put).partial_update(recommended: true)

You can also pass explicit request options to partial_update, by passing two explicit hashes:

# app/controllers/some_controller.rb

record.partial_update({ recommended: true }, { method: 'put' })

LHS injects parameters provided to create, update, partial_update, save etc. into an endpoint's URL when matching:

# app/models/feedback.rb

class Feedback << LHS::Record
  endpoint '{+service}/records/{record_id}/feedbacks'
end

# app/controllers/some_controller.rb

Feedback.create(record_id: 51232, text: 'Great Restaurant!')

POST https://service.example.com/records/51232/feedbacks { body: "{ 'text' : 'Great Restaurant!' }" }

In order to validate records before persisting them, you can use the valid? (validate alias) method.

It's not recommended to validate records anywhere, including application side validation via ActiveModel::Validations, except, if you validate them via the same endpoint/service, that also creates them.

The specific endpoint has to support validations without persistence. An endpoint has to be enabled (opt-in) in your record configurations:

# app/models/user.rb

class User < LHS::Record

  endpoint '{+service}/users', validates: { params: { persist: false } }

end

# app/controllers/some_controller.rb

user = User.build(email: 'i\'m not an email address')

unless user.valid?
  @errors = user.errors
  render 'new' and return
end

POST https://service.example.com/users?persist=false { body: '{ "email" : "i'm not an email address"}' }
{ 
  "field_errors": [{
    "path": ["email"],
    "code": "WRONG_FORMAT",
    "message": "The property value's format is incorrect."
  }],
  "message": "Email must have the correct format."
}

The functionalities of LHS::Errors pretty much follow those of ActiveModel::Validation:

# app/views/some_view.haml

@errors.any? # true
@errors.include?(:email) # true
@errors[:email] # ['WRONG_FORMAT']
@errors.messages # {:email=>["Translated error message that this value has the wrong format"]}
@errors.codes # {:email=>["WRONG_FORMAT"]}
@errors.message # Email must have the correct format."

The parameters passed to the validates endpoint option are used to perform record validations:

# app/models/user.rb

class User < LHS::Record

  endpoint '{+service}/users', validates: { params: { persist: false } }  # will add ?persist=false to the request
  endpoint '{+service}/users', validates: { params: { publish: false } }  # will add ?publish=false to the request
  endpoint '{+service}/users', validates: { params: { validates: true } } # will add ?validates=true to the request
  endpoint '{+service}/users', validates: { path: 'validate' }            # will perform a validation via ...users/validate

end

The HTTP status code received from the endpoint when performing validations on a record, is available through the errors object:

# app/controllers/some_controller.rb

record.save
record.errors.status_code # 400

Clear the error messages like:

# app/controllers/some_controller.rb

record.errors.clear

In case you want to add application side validation errors, even though it's not recommended, do it as following:

user.errors.add(:name, 'WRONG_FORMAT')

If you work with complex data structures, you sometimes need to have validation errors delegated/scoped to nested data.

This features makes LHS::Records compatible with how Rails or Simpleform renders/builds forms and especially error messages:

# app/controllers/some_controller.rb

unless @customer.save
  @errors = @customer.errors
end

POST https://service.example.com/customers { body: "{ 'address' : { 'street': 'invalid', housenumber: '' } }" }
{ 
  "field_errors": [{
    "path": ["address", "street"],
    "code": "REQUIRED_PROPERTY_VALUE_INCORRECT",
    "message": "The property value is incorrect."
  },{
    "path": ["address", "housenumber"],
    "code": "REQUIRED_PROPERTY_VALUE",
    "message": "The property value is required."
  }],
  "message": "Some data is invalid."
}

# app/views/some_view.haml

= form_for @customer, as: :customer do |customer_form|

  = fields_for 'customer[:address]', @customer.address, do |address_form|

    = fields_for 'customer[:address][:street]', @customer.address.street, do |street_form|

      = street_form.input :name
      = street_form.input :house_number

This would render nested forms and would also render nested form errors for nested data structures.

You can also access those nested errors like:

@customer.address.errors
@customer.address.street.errors

If a translation exists for one of the following translation keys, LHS will provide a translated error (also in the following order) rather than the plain error message/code, when building forms or accessing @errors.messages:

lhs.errors.records.<record_name>.attributes.<attribute_name>.<error_code>
e.g. lhs.errors.records.customer.attributes.name.unsupported_property_value

lhs.errors.records.<record_name>.<error_code>
e.g. lhs.errors.records.customer.unsupported_property_value

lhs.errors.messages.<error_code>
e.g. lhs.errors.messages.unsupported_property_value

lhs.errors.attributes.<attribute_name>.<error_code>
e.g. lhs.errors.attributes.name.unsupported_property_value

lhs.errors.fallback_message

lhs.errors.records.<record_name>.attributes.<collection>.<attribute_name>.<error_code>
e.g. lhs.errors.records.appointment_proposal.attributes.appointments.date_time.date_property_not_in_future

If an endpoint returns errors in the response body, that is enough to interpret it as: persistance failed. The response status code in this scenario is neglected.

In some cases, you need non blocking meta information about potential problems with the created record, so called warnings.

If the API endpoint implements warnings, returned when validating, they are provided just as errors (same interface and methods) through the warnings attribute:

# app/controllres/some_controller.rb

@presence = Presence.options(params: { synchronize: false }).create(
  place: { href: 'http://storage/places/1' }
)

POST https://service.example.com/presences { body: '{ "place": { "href": "http://storage/places/1" } }' }
{
    field_warnings: [{
      code: 'WILL_BE_RESIZED',
      path: ['place', 'photos', 0],
      message: 'This photo is too small and will be resized.'
    }
  }

presence.warnings.any? # true
presence.place.photos[0].warnings.messages.first # 'This photo is too small and will be resized.'

If you are using ActiveModel::Validations, even though it's not recommended, and you add errors to the LHS::Record instance, then those errors will be overwritten by the errors from ActiveModel::Validations when using save or valid?.

So in essence, mixing ActiveModel::Validations and LHS built-in validations (via endpoints), is not compatible, yet.

Open issue

Rails form_for view-helper can be used in combination with instances of LHS::Records to autogenerate forms:

<%= form_for(@instance, url: '/create') do |f| %>
  <%= f.text_field :name %>
  <%= f.text_area :text %>
  <%= f.submit "Create" %>
<% end %>

destroy deletes a record.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj

# app/controllers/some_controller.rb

record.destroy

DELETE https://service.example.com/records/1z-5r1fkaj

You can also destroy records directly without fetching them first:

# app/controllers/some_controller.rb

destroyed_record = Record.destroy('1z-5r1fkaj')

DELETE https://service.example.com/records/1z-5r1fkaj

or with parameters:

# app/controllers/some_controller.rb

destroyed_records = Record.destroy(name: 'Steve')

DELETE https://service.example.com/records?name='Steve'

Sometimes it is necessary to implement custom getters and setters and convert data to a processable (endpoint) format behind the scenes.

You can define setter methods in LHS::Records that will be used by initializers (new) and setter methods, that convert data provided, before storing it in the record and persisting it with a remote endpoint:

# app/models/user.rb

class Feedback < LHS::Record

  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end
end

# app/controllers/some_controller.rb

record = Record.new(ratings: { quality: 3 })
record.ratings # [{ :name=>:quality, :value=>3 }]

Setting attributes with other names:

# app/models/booking.rb

class Booking < LHS::Record

  def appointments_attributes=(values)
    self.appointments = values.map { |appointment| appointment[:id] }
  end
end

or

# app/models/booking.rb

class Booking < LHS::Record

  def appointments_attributes=(values)
    self[:appointments] = values.map { |appointment| appointment[:id] }
  end
end

# app/controllers/some_controller.rb

booking.update(params)

If you implement accompanying getter methods, the whole data conversion would be internal only:

# app/models/user.rb

class Feedback < LHS::Record

  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end

  def ratings
    super.map { |r| [r[:name], r[:value]] }]
  end
end

# app/controllers/some_controller.rb

record = Record.new(ratings: { quality: 3 })
record.ratings # {:quality=>3}

In a service-oriented architecture using hyperlinks/hypermedia, records/resources can contain hyperlinks to other records/resources.

When fetching records with LHS, you can specify in advance all the linked resources that you want to include in the results.

With includes LHS ensures that all matching and explicitly linked resources are loaded and merged (even if the linked resources are paginated).

Including linked resources/records is heavily influenced by https://guides.rubyonrails.org/active_record_querying.html and you should read it to understand this feature in all it's glory.

Sometimes you need to generate full hrefs/urls for records but you just have parameters that describe that record, like the ID.

For those usecases you can use href_for(params):

# app/controllers/some_controller.rb

Presence.create(place: { href: Place.href_for(123) })

POST '/presences' { place: { href: "http://datastore/places/123" } }

In case endpoints are paginated and you are certain that you'll need all objects of a set and not only the first page/batch, use includes.

LHS will ensure that all linked resources are around by loading all pages (parallelized/performance optimized).

# app/controllers/some_controller.rb

customer = Customer.includes(contracts: :products).find(1)

> GET https://service.example.com/customers/1
< {... contracts: { href: 'https://service.example.com/customers/1/contracts' } }
> GET https://service.example.com/customers/1/contracts?limit=100
< {... items: [...], limit: 10, offset: 0, total: 32 }
In parallel: 
  > GET https://service.example.com/customers/1/contracts?limit=10&offset=10
  < {... products: [{ href: 'https://service.example.com/product/LBC' }] }
  > GET https://service.example.com/customers/1/contracts?limit=10&offset=20
  < {... products: [{ href: 'https://service.example.com/product/LBB' }] }
In parallel:
  > GET https://service.example.com/product/LBC
  < {... name: 'Local Business Card' }
  > GET https://service.example.com/product/LBB
  < {... name: 'Local Business Basic' }

# app/controllers/some_controller.rb

customer.contracts.length # 32
customer.contracts.first.products.first.name # Local Business Card

includes_first_page includes the first page/response when loading the linked resource. If the endpoint is paginated, only the first page will be included.

# app/controllers/some_controller.rb

customer = Customer.includes_first_page(contracts: :products).find(1)

> GET https://service.example.com/customers/1
< {... contracts: { href: 'https://service.example.com/customers/1/contracts' } }
> GET https://service.example.com/customers/1/contracts?limit=100
< {... items: [...], limit: 10, offset: 0, total: 32 }
In parallel:
  > GET https://service.example.com/product/LBC
  < {... name: 'Local Business Card' }
  > GET https://service.example.com/product/LBB
  < {... name: 'Local Business Basic' }

# app/controllers/some_controller.rb

customer.contracts.length # 10
customer.contracts.first.products.first.name # Local Business Card

The method syntax of includes allows you to include hyperlinks stored in deep nested data structures:

Some examples:

Record.includes(:localch_account, :entry)
# Includes localch_account -> entry
# { localch_account: { href: '...', entry: { href: '...' } } }

Record.includes([:localch_account, :entry])
# Includes localch_account and entry
# { localch_account: { href: '...' }, entry: { href: '...' } }

Record.includes(campaign: [:entry, :user])
# Includes campaign and entry and user from campaign
# { campaign: { href: '...' , entry: { href: '...' }, user: { href: '...' } } }

When including linked resources with includes, already defined records and their endpoints and configurations are used to make the requests to fetch the additional data.

That also means that options for endpoints of linked resources are applied when requesting those in addition.

This applies for example a records endpoint configuration even though it's fetched/included through another record:

# app/models/favorite.rb

class Favorite < LHS::Record

  endpoint '{+service}/users/{user_id}/favorites', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint '{+service}/users/{user_id}/favorites/:id', auth: { basic: { username: 'steve', password: 'can' } }

end

# app/models/place.rb

class Place < LHS::Record

  endpoint '{+service}/v2/places', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint '{+service}/v2/places/{id}', auth: { basic: { username: 'steve', password: 'can' } }

end

# app/controllers/some_controller.rb

Favorite.includes(:place).where(user_id: current_user.id)

> GET https://service.example.com/users/123/favorites { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
< {... items: [... { place: { href: 'https://service.example.com/place/456' } } ] }
In parallel:
  > GET https://service.example.com/place/456 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
  > GET https://service.example.com/place/789 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
  > GET https://service.example.com/place/1112 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
  > GET https://service.example.com/place/5423 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }

Use references to apply request options to requests performed to fetch included records:

# app/controllers/some_controller.rb

Favorite.includes(:place).references(place: { auth: { bearer: '123' }}).where(user_id: 1)

GET https://service.example.com/users/1/favorites
{... items: [... { place: { href: 'https://service.example.com/places/2' } }] }
In parallel:
  GET https://service.example.com/places/2 { headers: { 'Authentication': 'Bearer 123' } }
  GET https://service.example.com/places/3 { headers: { 'Authentication': 'Bearer 123' } }
  GET https://service.example.com/places/4 { headers: { 'Authentication': 'Bearer 123' } }

Here is another example, if you want to ignore errors, that occur while you fetch included resources:

# app/controllers/some_controller.rb

feedback = Feedback
  .includes(campaign: :entry)
  .references(campaign: { ignore: LHC::NotFound })
  .find(12345)

In case you include nested data and ignored errors while including, it can happen that you get back a collection that contains data based on response errors:

# app/controllers/some_controller.rb

user = User
  .includes(:places)
  .references(places: { ignore: LHC::NotFound })
  .find(123)

GET http://service/users/123
{ "places": { "href": "http://service/users/123/places" } }

GET http://service/users/123/places
{ "items": [
  { "href": "http://service/places/1" },
  { "href": "http://service/places/2" }
] }

GET http://service/places/1
200 { "name": "Casa Ferlin" }

GET http://service/places/2
404 { "status": 404, "error": "not found" }

user.places[1] # { "status": 404, "error": "not found" }

In order to exclude items from a collection which where not based on successful responses, use .compact or .compact!:

# app/controllers/some_controller.rb

user = User
  .includes(:places)
  .references(places: { ignore: LHC::NotFound })
  .find(123)
places = user.places.compact

places # { "items": [ { "href": "http://service/places/1", "name": "Casa Ferlin" } ] }

Be careful using methods for batch processing. They could result in a lot of HTTP requests!

all fetches all records from the service by doing multiple requests, best-effort parallelization, and resolving endpoint pagination if necessary:

records = Record.all

> GET https://service.example.com/records?limit=100
< {...
  items: [...]
  total: 900,
  limit: 100,
  offset: 0
}
In parallel:
  > GET https://service.example.com/records?limit=100&offset=100
  > GET https://service.example.com/records?limit=100&offset=200
  > GET https://service.example.com/records?limit=100&offset=300
  > GET https://service.example.com/records?limit=100&offset=400
  > GET https://service.example.com/records?limit=100&offset=500
  > GET https://service.example.com/records?limit=100&offset=600
  > GET https://service.example.com/records?limit=100&offset=700
  > GET https://service.example.com/records?limit=100&offset=800

all is chainable and has the same interface like where:

Record.where(color: 'blue').all
Record.all.where(color: 'blue')
Record.all(color: 'blue')

All three are doing the same thing: fetching all records with the color 'blue' from the endpoint while resolving pagingation if endpoint is paginated.

In case an API does not provide pagination information in the repsponse data (limit, offset and total), LHS keeps on loading pages when requesting all until the first empty page responds.

find_each is a more fine grained way to process single records that are fetched in batches.

Record.find_each(start: 50, batch_size: 20, params: { has_reviews: true }, headers: { 'Authorization': 'Bearer 123' }) do |record|
  # Iterates over each record. Starts with record no. 50 and fetches 20 records each batch.
  record
  break if record.some_attribute == some_value
end

find_in_batches is used by find_each and processes batches.

Record.find_in_batches(start: 50, batch_size: 20, params: { has_reviews: true }, headers: { 'Authorization': 'Bearer 123' }) do |records|
  # Iterates over multiple records (batch size is 20). Starts with record no. 50 and fetches 20 records each batch.
  records
  break if records.first.name == some_value
end

Based on ActiveRecord's implementation, LHS implements becomes, too.

It's a way to convert records of a certain type A to another certain type B.

NOTE: RPC-style actions, that are discouraged in REST anyway, are utilizable with this functionality, too. See the following example:

# app/models/location.rb

class Location < LHS::Record
  endpoint '{+service}/locations'
  endpoint '{+service}/locations/{id}'
end

# app/models/synchronization.rb

class Synchronization < LHS::Record
  endpoint '{+service}/locations/{id}/sync'
end

# app/controllers/some_controller.rb

location = Location.find(1)

GET https://service.example.com/location/1

# app/controllers/some_controller.rb

synchronization = location.becomes(Synchronization)
synchronization.save!

POST https://service.example.com/location/1/sync { body: '{ ... }' }

Allows you to set the attributes by passing in a hash of attributes.

entry = LocalEntry.new
entry.assign_attributes(company_name: 'localsearch')
entry.company_name # => 'localsearch'

By default, LHS does not perform the same http request multiple times during one request/response cycle.

# app/models/user.rb

class User < LHS::Record
  endpoint '{+service}/users/{id}'
end

# app/models/location.rb

class Location < LHS::Record
  endpoint '{+service}/locations/{id}'
end

# app/controllers/some_controller.rb

def index
  @user = User.find(1)
  @locations = Location.includes(:owner).find(2)
end

GET https://service.example.com/users/1
GET https://service.example.com/location/2
{... owner: { href: 'https://service.example.com/users/1' } }
From cache:
  GET https://service.example.com/users/1

It uses the LHC Caching Interceptor as caching mechanism base and sets a unique request id for every request cycle with Railties to ensure data is just cached within one request cycle and not shared with other requests.

Only GET requests are considered for caching by using LHC Caching Interceptor's cache_methods option internally and considers request headers when caching requests, so requests with different headers are not served from cache.

The LHS Request Cycle Cache is opt-out, so it's enabled by default and will require you to enable the LHC Caching Interceptor in your project.

By default the LHS Request Cycle Cache will use ActiveSupport::Cache::MemoryStore as its cache store. Feel free to configure a cache that is better suited for your needs by:

# config/initializers/lhs.rb

LHS.configure do |config|
  config.request_cycle_cache = ActiveSupport::Cache::MemoryStore.new
end

If you want to disable the LHS Request Cycle Cache, simply disable it within configuration:

# config/initializers/lhs.rb

LHS.configure do |config|
  config.request_cycle_cache_enabled = false
end

LHS provides a way to have records automatically fetch and use OAuth authentication when performing requests within Rails.

In order to enable automatic oauth authentication, perform the following steps:

1. Make sure LHS is configured to perform auto_oauth. Provide a block that, when executed in the controller context, returns a valid access_token/bearer_token.

# config/initializers/lhs.rb

LHS.configure do |config|
  config.auto_oauth = -> { access_token }
end

2. Opt-in records requiring oauth authentication:

# app/models/record.rb

class Record < LHS::Record
  oauth
  # ...
end

3. Include the LHS::OAuth context into your application controller:

# app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  include LHS::OAuth

  # ...
end

4. Make sure you have the LHC::Auth interceptor enabled:

# config/initializers/lhc.rb

LHC.configure do |config|
  config.interceptors = [LHC::Auth]
end

Now you can perform requests based on the record that will be auto authenticated from now on:

# app/controllers/some_controller.rb

Record.find(1)

https://records/1
Authentication: 'Bearer token-12345'

In case you need to configure multiple auth provider access_tokens within your application, make sure you provide a proc returning a hash when configuring auto_oauth, naming every single provider and the responsive method to retrieve the access_tokens in the controller context:

# config/initializers/lhs.rb
LHS.configure do |config|
  config.auto_oauth = proc do
    {
      provider1: access_token_provider_1,
      provider2: access_token_provider_2
    }
  end
end

Then make sure you either define which provider to use on a record level:

# model/record.rb
class Record < LHS::Record
  oauth(:provider1)
  #...
end

or on an endpoint level:

# model/record.rb
class Record < LHS::Record
  endpoint 'https://service/records', oauth: :provider1
  #...
end

If you're using LHS service providers, you can also configure auto auth on a provider level:

# app/models/providers/localsearch.rb
module Providers
  class Localsearch < LHS::Record
    
    provider(
      oauth: true
    )
  end
end

or with multiple auth providers:

# app/models/providers/localsearch.rb
module Providers
  class Localsearch < LHS::Record
    
    provider(
      oauth: :provider_1
    )
  end
end

In order to apply options to all requests performed in a give block, LHS provides option blocks.

# app/controllers/records_controller.rb

LHS.options(headers: { 'Tracking-Id' => 123 }) do
  Record.find(1)
end

Record.find(2)

GET https://records/1 { headers: { 'Tracking-Id' => '123' } }
GET https://records/2 { headers: { } }

LHS supports tracing the source (in your application code) of http requests being made with methods like find find_by find_by! first first! last last!.

Following links, and using includes are not traced (just yet).

In order to enable tracing you need to enable it via LHS configuration:

# config/initializers/lhs.rb

LHS.configure do |config|
  config.trace = Rails.env.development? || Rails.logger.level == 0 # debug
end

# app/controllers/application_controller.rb

code = Code.find(code: params[:code])

Called from onboarding/app/controllers/concerns/access_code_concern.rb:11:in `access_code'

However, following links and includes won't get traced (just yet):

# app/controllers/application_controller.rb

code = Code.includes(:places).find(123)

# Nothing is traced
{
  places: [...]
}

code.places

{ 
  token: "XYZABCDEF",
  places:
    [
      { href: "http://storage-stg.preprod-local.ch/v2/places/egZelgYhdlg" }
    ]
}

In order to log all requests/responses prior to an exception reported by Rollbar in addition to the exception itself, use the LHS::ExtendedRollbar interceptor in combination with the rollbar processor/handler:

# config/initializers/lhc.rb

LHC.configure do |config|
  config.interceptors = [LHS::ExtendedRollbar]
end

# config/initializers/rollbar.rb

Rollbar.configure do |config|
  config.before_process << LHS::Interceptors::ExtendedRollbar::Handler.init
end

Best practice in regards of testing applications using LHS, is to let LHS fetch your records, actually perform HTTP requests and WebMock to stub/mock those http requests/responses.

This follows the Black Box Testing approach and prevents you from creating constraints to LHS' internal structures and mechanisms, which will break as soon as we change internals.

# specs/*/some_spec.rb 

let(:contracts) do
  [
    {number: '1'},
    {number: '2'},
    {number: '3'}
  ]
end

before do
  stub_request(:get, "https://service.example.com/contracts")
    .to_return(
      body: {
        items: contracts,
        limit: 10,
        total: contracts.length,
        offset: 0
      }.to_json
    )
end

it 'displays contracts' do
  visit 'contracts'
  contracts.each do |contract|
    expect(page).to have_content(contract[:number])
  end
end

In order to load LHS test helpers into your tests, add the following to your spec helper:

# spec/spec_helper.rb

require 'lhs/rspec'

This e.g. will prevent running into caching issues during your tests, when (request cycle cache)[#request-cycle-cache] is enabled. It will initialize a MemoryStore cache for LHC::Caching interceptor and resets the cache before every test.

LHS offers stub helpers that simplify stubbing https request to your apis through your defined Records.

Record.stub_all(url, items, additional_options)

# your_spec.rb

before do
  class Record < LHS::Record
    endpoint 'https://records'
  end

  Record.stub_all(
    'https://records',
    200.times.map{ |index| { name: "Item #{index}" } },
    headers: {
      'Authorization' => 'Bearer 123'
    }
  )
end

GET https://records?limit=100
GET https://records?limit=100&offset=100

LHS also uses Record configuration when stubbing all.

# your_spec.rb

before do
  class Record < LHS::Record
    configuration limit_key: :per_page, pagination_strategy: :page, pagination_key: :page

    endpoint 'https://records'
  end

  Record.stub_all(
    'https://records',
    200.times.map{ |index| { name: "Item #{index}" } }
  )
end

GET https://records?per_page=100
GET https://records?per_page=100&page=2

Use fetch in tests to resolve chains in place and expect WebMock stubs to be requested.

# specs/*/some_spec.rb 

records = Record.where(color: 'blue').where(available: true).where(color: 'red')

expect(
  records.fetch
).to have_requested(:get, %r{records/})
  .with(query: hash_including(color: 'blue', available: true))

As where chains are not resolving to HTTP-requests when no data is accessed, you can use where_values_hash to access the values that would be used to resolve the chain, and test those:

# specs/*/some_spec.rb 

records = Record.where(color: 'blue').where(available: true).where(color: 'red')

expect(
  records.where_values_hash
).to eq {color: 'red', available: true}

GNU General Public License Version 3.