Module: CodyRobbins::DeclarativeFind::ClassMethods

Defined in:
lib/cody_robbins/declarative_find/class_methods.rb

Instance Method Summary collapse

Instance Method Details

#find(name, options = {}, &block) ⇒ Object

Creates a before filter on the controller that finds an ActiveRecord instance and assigns it to an instance variable.

  • You pass the name of the model to look up to the method.
  • By default the key in params assumed to contain the ID of the record to find is either :id or, if :id is not present, then extrapolated from the model name. For example, if the model is User then this key would be :user. Preference is given to :id to prevent conflicts in situations such as edit actions, where a record is looked up but new values for its attributes are passed via a key in params sharing the name of the model. For example, if the model is User then params[:user] would contain the attributes for the user from the form, and :id would have to be used to specify the ID of the user in question.
  • By default the instance variable that the record is assigned to will be named according to the model. For example, if the model is User then the instance variable will be @user.
  • This behavior can be customized any which way via different combinations of options.

An 404 HTTP code will be returned and the corresponding error page rendered for non-existent records via the http-error gem.

Examples:

Straight-forward lookup. This example assumes the request for the delete action has an :id or :user param passed to it containing the ID of the user to delete.

class UserController < ApplicationController
  find(:user)

  def delete
    @user.destroy
  end
end

Overriding the name of the parameter containing the ID of the model. This example assumes the request for the delete action has a :user_id param passed to it containing the ID of the user to delete.

class UserController < ApplicationController
  find(:user, :param => :user_id)

  def delete
    @user.destroy
  end
end

Overriding the name of the instance variable used to store the record. This example assumes the request for the delete action has an :id or :user param passed to it containing the ID of the user to delete.

class UserController < ApplicationController
  find(:user, :variable => :user_to_delete)

  def delete
    @user_to_delete.destroy
  end
end

Using a method to provide custom logic for the lookup of the model.

class UserController < ApplicationController
  find(:user)

  def delete
    @user.destroy
  end

  protected

  def find_user
    User.find_by_email(params[:email])
  end
end

Using a custom-named method to provide the logic for the lookup of the model.

class UserController < ApplicationController
  find(:user, :using => :find_user_by_email)

  def delete
    @user.destroy
  end

  protected

  def find_user_by_email
    User.find_by_email(params[:email])
  end
end

Using a Proc to provide custom logic for the lookup of the model.

class UserController < ApplicationController
  find(:user, :using => proc { User.find_by_email(params[:email]) })

  def delete
    @user.destroy
  end

  protected

  def find_user_by_email
    User.find_by_email(params[:email])
  end
end

Using a block to provide custom logic for the lookup of the model.

class UserController < ApplicationController
  find(:user) { User.find_by_email(params[:email]) }

  def delete
    @user.destroy
  end
end

Restricting the lookup to specific actions.

class UserController < ApplicationController
  find(:user, :only => :delete)

  def delete
    @user.destroy
  end

  def something_else
    render(:text => 'Something else.')
  end
end

Parameters:

  • name (Symbol, String) —

    The name of the model to look up.

  • options (Hash) (defaults to: {}) —

    Any options not specifically used by the plugin method are simply passed through to the underlying before_filter. For example, you could limit the lookup to a specific action by including the :only option.

Options Hash (options):

  • :param (String, Symbol) —

    The key used to look up the record’s ID in the params hash. It defaults to the name of the model. For example, if the model is User then this option will default to :user.

  • :variable (String, Symbol) —

    The name of the instance variable to assign the looked up object to. It defaults to the name of the model. For example, if the model is User then this option will default to :user.

  • :using (String, Symbol, Proc) —

    If this option is string or symbol, it represents the name of a method on the controller that will be invoked in order to perform the look up. If it’s a Proc, then the proc is invoked to perform the look up. In either case, the return value should be the object to assign to the instance variable. This option can be used when custom logic needs to be provided to find a record beyond simply looking up by its ID. This option defaults to :find_ prepended to the name of the model. For example, if the model is User then this option will default to :find_user.



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# File 'lib/cody_robbins/declarative_find/class_methods.rb', line 107

def find(name, options = {}, &block)
  options.reverse_merge!(:param    => name,
                         :variable => name,
                         :using    => "find_#{name}")

  model         = name.to_class
  param_name    = options.delete(:param)
  variable_name = options.delete(:variable)
  lookup_method = options.delete(:using)

  before_filter(options) do
    object = if block_given?
               yield
             elsif lookup_method.is_a?(Proc)
               lookup_method.call
             elsif lookup_method.respond_to?(:to_s) && respond_to?(lookup_method.to_s)
               send(lookup_method.to_s)
             else
               id = params[:id] || params[param_name]
               model.find_by_id(id)
             end

    if object
      set_instance_variable(variable_name, object)
    else
      http_error(404)
    end
  end
end