Module: ActiveRecord::Associations::ClassMethods

Defined in:
lib/has_and_belongs_to_many_with_deferred_save.rb

Instance Method Summary collapse

Instance Method Details

#has_and_belongs_to_many_with_deferred_save(*args) ⇒ Object

Instructions:

Replace your existing call to has_and_belongs_to_many with has_and_belongs_to_many_with_deferred_save.

Then add a validation method that adds an error if there is something wrong with the (unsaved) collection. This will prevent it from being saved if there are any errors.

Example:

def validate
  if people.size > maximum_occupancy
    errors.add :people, "There are too many people in this room"
  end
end



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# File 'lib/has_and_belongs_to_many_with_deferred_save.rb', line 20

def has_and_belongs_to_many_with_deferred_save(*args)
  has_and_belongs_to_many *args
  collection_name = args[0].to_s
  collection_singular_ids = collection_name.singularize + "_ids"

  # this will delete all the assocation into the join table after obj.destroy
  after_destroy { |record| record.save }

  attr_accessor :"unsaved_#{collection_name}"
  attr_accessor :"use_original_collection_reader_behavior_for_#{collection_name}"

  define_method "#{collection_name}_with_deferred_save=" do |collection|
    #puts "has_and_belongs_to_many_with_deferred_save: #{collection_name} = #{collection.collect(&:id).join(',')}"
    self.send "unsaved_#{collection_name}=", collection
  end

  define_method "#{collection_name}_with_deferred_save" do |*args|
    if self.send("use_original_collection_reader_behavior_for_#{collection_name}")
      self.send("#{collection_name}_without_deferred_save")
    else
      if self.send("unsaved_#{collection_name}").nil?
        send("initialize_unsaved_#{collection_name}", *args)
      end
      self.send("unsaved_#{collection_name}")
    end
  end

  alias_method_chain :"#{collection_name}=", 'deferred_save'
  alias_method_chain :"#{collection_name}", 'deferred_save'

  define_method "#{collection_singular_ids}_with_deferred_save" do |*args|
    if self.send("use_original_collection_reader_behavior_for_#{collection_name}")
      self.send("#{collection_singular_ids}_without_deferred_save")
    else
      if self.send("unsaved_#{collection_name}").nil?
        send("initialize_unsaved_#{collection_name}", *args)
      end
      self.send("unsaved_#{collection_name}").map { |e| e[:id] }
    end
  end

  alias_method_chain :"#{collection_singular_ids}", 'deferred_save'


  define_method "before_save_with_deferred_save_for_#{collection_name}" do
    # Question: Why do we need this @use_original_collection_reader_behavior stuff?
    # Answer: Because AssociationCollection#replace(other_array) performs a diff between current_array and other_array and deletes/adds only
    # records that have changed.
    # In order to perform that diff, it needs to figure out what "current_array" is, so it calls our collection_with_deferred_save, not
    # knowing that we've changed its behavior. It expects that method to return the elements of that collection that are in the *database*
    # (the original behavior), so we have to provide that behavior...  If we didn't provide it, it would end up trying to take the diff of
    # two identical collections so nothing would ever get saved.
    # But we only want the old behavior in this case -- most of the time we want the *new* behavior -- so we use
    # @use_original_collection_reader_behavior as a switch.

    if self.respond_to? :"before_save_without_deferred_save_for_#{collection_name}"
      self.send("before_save_without_deferred_save_for_#{collection_name}")
    end

    self.send "use_original_collection_reader_behavior_for_#{collection_name}=", true
    if self.send("unsaved_#{collection_name}").nil?
      send("initialize_unsaved_#{collection_name}", *args)
    end
    self.send "#{collection_name}_without_deferred_save=", self.send("unsaved_#{collection_name}")
      # /\ This is where the actual save occurs.
    self.send "use_original_collection_reader_behavior_for_#{collection_name}=", false

    true
  end
  alias_method_chain :"before_save", "deferred_save_for_#{collection_name}"


  define_method "reload_with_deferred_save_for_#{collection_name}" do
    # Reload from the *database*, discarding any unsaved changes.
    returning self.send("reload_without_deferred_save_for_#{collection_name}") do
      self.send "unsaved_#{collection_name}=", nil
        # /\ If we didn't do this, then when we called reload, it would still have the same (possibly invalid) value of
        # unsaved_collection that it had before the reload.
    end
  end
  alias_method_chain :"reload", "deferred_save_for_#{collection_name}"


  define_method "initialize_unsaved_#{collection_name}" do |*args|
    #puts "Initialized to #{self.send("#{collection_name}_without_deferred_save").clone.inspect}"
    self.send "unsaved_#{collection_name}=", self.send("#{collection_name}_without_deferred_save", *args).clone
      # /\ We initialize it to collection_without_deferred_save in case they just loaded the object from the
      # database, in which case we want unsaved_collection to start out with the "saved collection".
      # If they just constructed a *new* object, this will still work, because self.collection_without_deferred_save.clone
      # will return a new HasAndBelongsToManyAssociation (which acts like an empty array, []).
      # Important: If we don't use clone, then it does an assignment by reference and any changes to unsaved_collection
      # will also change *collection_without_deferred_save*! (Not what we want! Would result in us saving things
      # immediately, which is exactly what we're trying to avoid.)

    # trick collection_name.include?(obj)
    # If you use a collection of SignelTableInheritance and didn't :select 'type' the
    # include? method will not find any subclassed object.
    class << eval("@unsaved_#{collection_name}")
      def include_with_deferred_save?(obj)
        if self.detect { |itm| itm == obj || (itm[:id] == obj[:id] && obj.is_a?(itm.class) ) }
          return true
        else
          return false
        end
      end
      alias_method_chain :include?, 'deferred_save'
    end


    collection_without_deferred_save =  self.send("#{collection_name}_without_deferred_save")
    # (We don't have access to locals inside a normal class << object block, so we have to do it this way instead.)
    (class << eval("@unsaved_#{collection_name}"); self end).class_eval do
      define_method :find do |*args|
        collection_without_deferred_save.send(:find, *args)
      end
      # We have to override these so that it doesn't call Array's version of these methods.
      # Otherwise user will get a "can't convert Hash into Integer" error
      define_method :first do |*args|
        collection_without_deferred_save.send(:first, *args)
      end
      define_method :last do |*args|
        collection_without_deferred_save.send(:first, *args)
      end

      define_method :method_missing do |method, *args|
        #puts "#{self.class}.method_missing(#{method}) (#{collection_without_deferred_save.inspect})"
        collection_without_deferred_save.send(method, *args)
      end
    end

  end
  private :"initialize_unsaved_#{collection_name}"

end