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Clean Validations with Custom Contexts

Clean Validations with Custom Contexts

clean validations with custom contexts

 

Active Record validations are well-known and widely used in Rails.

 

class User < ApplicationRecord
validates :name, presence: { message: "must be given please" }
end

 

This runs the validation on save, both when creating a new record or when updating an existing record.

on option allows control over when to run the validation, commonly used with value of create or update

 

class User < ApplicationRecord
  belongs_to :club, optional: true 
  validates :name, presence: { message: "must be given please" }, on: :create
  validates :club, presence: { message: "must be given please" }, on: :update  
end

 

This allows creating users without associating them with a Club but enforces the presence of Club on subsequent updates. This pattern is commonly used to allow users to signup with bare minimum form fields and then forcing them to update their profiles with more information on subsequent visits.

Value for the on option is not limited to create and update, we can have our own custom contexts. Like in a multistep form, we can have validations for each of the steps. on options makes this really easy to do

 

class User < ApplicationRecord
  validate :basic_info, on: :basic_info
  validate :education_details, on: :education_details
  validate :professional_info, on: :professional_info
  private
  def basic_info
    # Validation for basic info, first_name, last_name, email
  end
  def education_details
    # Validation for education_details
  end
  def professional_info
    # Validation for professional_info
  end
end

 

In the controller

 

class UsersController < ApplicationController
  ...
  def update_basic_info
    @user.assign_attributes(basic_info_params)
    @user.save(:basic_info)
  end
  def update_education_details
    @user.assign_attributes(education_details_params)
    @user.save(:education_details)
  end
  def update_professional_info
    @user.assign_attributes(professional_info_params)
    @user.save(:professional_info)
  end
  private
  def basic_info_params
    # strong params
  end
  def education_details_params
    # strong params
  end
  def professional_info_params
    # strong params
  end
end

 

With Rails 5 adding support for multiple contexts, we can use multiple contexts together

 

@user.save(:basic_info, :professional_info)

 

This seems pretty neat, let’s go a step further and do this with update_attributes. In current implementation of Rails,
update_attributes does not support validation contexts. We can get around this by defining our own custom method

 

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
  def update_attibutes_with_context(attributes, *contexts)
    with_transaction_returning_status do
      assign_attributes(attributes)
      save(context: contexts)
    end
  end
end

 

In the controller

 

@user.update_attibutes_with_context({first_name: 'fname'}, :basic_info)

 

Lastly, we can use with_options to group multiple validations within a context

 

with_options on: :member do |member_user|
    member_user.validates :club_name, presence: true
    member_user.validates :membership_id, presence: true
  end

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