Mongoid::DynamicClients

Mongoid::DynamicClients helps MongoId enabled apps to talk to multiple MongoDB databases. It is dynamic in the sense that you do not necessary have to know the databases you're connecting to beforehand. Instead you provide connection properties (i.e. auth. credentials, hosts etc) at runtime so you can get them gotten from a DB or receive from an other source.

In the example below the connection properties come from the config hash:

require "mongoid/dynamic_clients"

# the database to connect to:
config = { 
  database: 'my_custom_db',
  hosts: ['https://foobar.mongo.com:27017'],
  options: {
    user: 'default_user',
    password: 'default_password',
    auth_source: 'admin'
   }
}

# connect and execute the block against that database:
with_mongoid_client(:my_custom_db, config) do
  Record.create!(foo: "bar")
end

Add this line to your application's Gemfile:

gem 'mongoid-dynamic_clients'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mongoid-dynamic_clients

Mongoid::DynamicClients extends MongoId a little bit to make it easier to switch databases at runtime without the need to configure them all in mongoid.yml file. This is helpful when you do not know the databases you're connecting to at the build time, say you're developing a multi-tenancy or a white-labeable application where every tenant has its own database and you do not have the ability to enumerate them all in mongoid.yml.

Let's put it straight - both clients and databases terms are used interchangeably in this document. It is because MongoId (and the underlying mongodb driver) use the mention of client - a thing that is responsible for maintaining connections to the database and perform basic operations against it. Regular people though would call it database - i.e. let it connect to database A and then connect to database B... So the document uses the two terms in the same meaning so both, experienced and regular developers would understand what's going on here.

When MongoId gem is installed and set up, it generates a mongoid.yml config file. The file features a single client (database) that is used by default and has the name of default:

production:
  # Configure available database clients. (required)
  clients:
    # Defines the default client. (required)
    default:
      database: default
      hosts:
        - 'localhost:27017'
      options:
        user: 'default_user'
        password: 'default_password'
        auth_source: admin

This is default client/database the application will use when it starts up.

The idea behind the Mongoid::DynamicClients is to switch the databases at runtime, for this it provides a single with_mongoid_client method that takes care of the job:

# this goes to the `default` database
Record.create!()

# queries within the block go to the `my_custom_db` database
with_mongoid_client(:my_custom_db, config) do
  Record.create!() 
end

# this goes back to the `default` database
Record.create!() 

(the code above assumes that Record is a MongoId document)

The second argument of the with_mongoid_client method is a configuration hash. It is supposed to convey connection information for given database. The structure of the config hash is the reflection of the client structure seen in mongoid.yml file above:

default:
  database: default
  hosts:
    - 'localhost:27017'
  options:
    user: 'default_user'
    password: 'default_password'
    auth_source: adminkm

so, config hash should be a structure like this:

config = {
  database: 'default',
  hosts: [ 'localhost:27017' ],
  options: {
    user: 'default_user',
    password: 'default_password',
    auth_source: 'admin'
  }
}

with_mongoid_client(:my_custom_db, config) do
  Record.create!() 
end

Note: any other client options available in mongoid.yml can be specified in the configuration hash, so that's how you may configure connection pooling and other options for the client.

todo: Explain how Core Mongoid Threaded works, where the clients are stored and how that affects code

todo: Describe puma setup, how threads are managed and how that affects multi database connections

todo: Describe the theading model behind sidekiq, provide a code sample of the use of dynamic clients in a sidekiq job

todo: It is easy to get out of connection pool limits by passing connection pool configuration to with_mongoid_client - explain the danger of that.

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/mongoid-dynamic_clients. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.