Question

I’m fairly new to Rails, I got this code working but I think I’m preventing it from doing it some of its Rails magic:

Goal: Create a cause and have the creator become a member via the build method and the has_many :through association in the Cause_User_Membership table.

Question: I’ve gotten it to work, by creating a cause and then creating a membership ‘manually.’ Is there a way for the Cause_User_Membership relationship to be created automatically on the creation of a cause?

Cause_Controller.rb

def create
@cause = current_user.causes.build(params[:cause].merge :created_by => current_user.id)

respond_to do |format|
  if @cause.save 
    @membership = current_user.cause_user_memberships.build(:cause_id => @cause.id)
    @membership.save
    format.json { render :json => {current_user: current_user, results: @cause}}
  else
    format.json { render :json => {Message: "You messed up"}}
  end
end
end

User.rb (snippet)

has_many :cause_user_memberships
has_many :causes, :through => :cause_user_memberships

Cause.rb

attr_accessible :title, :location, :description,...
has_many :cause_user_memberships
has_many :users, :through => :cause_user_memberships

Cause_User_Membership.rb (<–probably not my best model name)

    # == Schema Information
#
# Table name: cause_user_memberships
#
#  id         :integer          not null, primary key
#  user_id    :integer          not null
#  cause_id   :integer          not null
#  created_at :datetime         not null
#  updated_at :datetime         not null
#

class CauseUserMembership < ActiveRecord::Base
  attr_accessible :cause_id, :user_id

  belongs_to :user #, :class_name => "User", :foreign_key => "user_id" 
  belongs_to :cause #, :class_name => "Cause", :foreign_key => "cause_id"

end

Answer 1

Update:

I found a slightly more “magical” way to do this using accepts_nested_attributes_for. First, add a line to your CauseUserMembership model:

class CauseUserMembership < ActiveRecord::Base
  attr_accessible :cause_id, :user_id

  belongs_to :user
  belongs_to :cause 

  accepts_nested_attributes_for :cause

With that change, you can do this:

def create
  @membership = current_user.memberships.build
  @membership.cause = Cause.new(params[:cause].merge(:created_by => current_user.id)

  respond_to do |format|
    if @membership.save
      ...

Because you have told rails to accept nested attributes for the cause association on CauseUserMembership, it will save the new cause you assigned to @membership.cause when it saves the membership itself. So you can save both the cause and membership records at one time, rather than separately.

Original answer:

I think what you’ve done is pretty much the right way to do this. It can be simplified a tad bit: you don’t need to build cause from current_user, you can just use new (the :through associations on cause and current_user are set when you create @membership).

So like this (I only changed the first line in create):

def create
  @cause = Cause.new(params[:cause].merge(:created_by => current_user.id))

  respond_to do |format|
    if @cause.save
      @membership = current_user.cause_user_memberships.build(:cause_id => @cause.id)
      @membership.save
      ...

See also: Many-to-Many through association Build/Create properties in Rails app