Valhammer

Automatically validate ActiveRecord models based on the database schema.

Copyright 2015-2016, Australian Access Federation

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Add this line to your application's Gemfile:

gem 'valhammer'

Use Bundler to install the dependency:

bundle install

In Rails, Valhammer is automatically added to ActiveRecord::Base. If you're using ActiveRecord outside of Rails, you may have to do this yourself:

ActiveRecord::Base.extend(Valhammer::Validations)

Call the valhammer method inside your model class, after any belongs_to relationships are defined:

class Widget < ActiveRecord::Base
  belongs_to :supplier

  valhammer
end

Generated validations are:

• :presence — added to non-nullable, non-boolean columns
• :inclusion — added to boolean columns to emulate the functionality of presence which doesn't work correctly for booleans
• :uniqueness — added to match unique keys
• :numericality — added to integer/decimal columns with the only_integer option set appropriately
• :length — added to string columns to ensure the value fits in the column

SQLite Note: In SQLite, a string column has no default length restriction (except for the hard limit on data size set at compile time). Valhammer will not apply a length validation unless the column was created with an explicit limit.

Passing a block to valhammer allows some selective calls to disable to customise the validators which are applied to your model:

class Widget < ActiveRecord::Base
  valhammer do
    disable item_code: [:presence, :uniqueness]
  end
end

Disabling an attribute instructs Valhammer not to apply any validators for that attribute:

class Widget < ActiveRecord::Base
  valhammer do
    disable :supplier_code
  end
end

When disabling validations for an association, disable the validations on the association name, not the name of the foreign key column:

class Widget < ActiveRecord::Base
  belongs_to :supplier

  valhammer do
    disable supplier: :presence
  end
end

When Valhammer encounters a composite unique key, it inspects the columns involved in the key and uses them to build a scope. For example:

create_table(:widgets) do |t|
  t.string :supplier_code, null: false, default: nil
  t.string :item_code, null: false, default: nil

  t.index [:supplier_code, :item_code], unique: true
end

When this table is examined by Valhammer, the uniqueness validation created will be the same as if you had written:

class Widget < ActiveRecord::Base
  validates :item_code, uniqueness: { scope: :supplier_code }
end

That is, the last column in the key is the field which gets validated, and the other columns form the scope argument.

If any of the scope columns are nullable, the validation will be conditional on the presence of the scope values. This avoids the situation where your underlying database would accept a row (because it considers NULL values not equal to each other, which is true of SQLite, PostgreSQL and MySQL/MariaDB at the least.)

If the above example table had nullable columns, for example:

create_table(:widgets) do |t|
  t.string :supplier_code, null: true, default: nil
  t.string :item_code, null: true, default: nil

  t.index [:supplier_code, :item_code], unique: true
end

This amended table structure causes Valhammer to create validations as though you had written:

class Widget < ActiveRecord::Base
  validates :item_code, uniqueness: { scope: :supplier_code,
                                      if: -> { supplier_code },
                                      allow_nil: true }
end

Valhammer is able to handle the simple case when multiple unique keys reference the same field, as in the following contrived example:

create_table(:order_update) do |t|
  t.belongs_to :order
  t.string :state
  t.string :identifier

  t.index [:order_id, :state], unique: true
  t.index [:order_id, :state, :identifier], unique: true
end

Uniqueness validations are created as though the model was defined using:

class OrderUpdate < ActiveRecord::Base
  validates :state, uniqueness: { scope: :order_id }
  validates :identifier, uniqueness: { scope: [:order_id, :state] }
end

In the case where multiple unique keys have the same column in the last position, Valhammer is unable to determine which is the "authoritative" scope for the validation. Take the following contrived example:

create_table(:order_enquiry) do |t|
  t.belongs_to :order
  t.belongs_to :customer
  t.string :date

  t.index [:order_id, :date], unique: true
  t.index [:customer_id, :date], unique: true
end

Valhammer is unable to resolve which scope to apply, so no uniqueness validation is applied.

In the case where a foreign key is the last column in a key, that key will not be given a uniqueness validation.

create_table(:order_payment) do |t|
  t.belongs_to :customer
  t.string :reference
  t.boolean :complete
  t.integer :amount

  t.index [:reference, :customer_id], unique: true
end

To work around this, put associations first in your unique keys (often a good idea anyway, if it means your association queries benefit from the index).

Alternatively, apply the validation yourself using ActiveRecord.

When a unique key is partially applied to a relation, that key will not be given a uniqueness validation.

create_table(:widgets) do |t|
  t.string :supplier_code, null: true, default: nil
  t.string :item_code, null: true, default: nil

  t.index [:supplier_code, :item_code], unique: true,
                                        where: 'item_code LIKE "a%"'
end

In this case, it is not possible for valhammer to determine the behaviour of the where clause, so the validation must be manually created.

To make Valhammer tell you exactly what it's doing, turn on verbose mode:

Valhammer.config.verbose = true

Refer to GitHub Flow for help contributing to this project.