Rails 4 - has_and_belongs_to_many assocation

Question

I created a has_and_belongs_to_many association between users and projects so that a user would be able to join in on a project. The association table exists however, I am unsure how I would create the association.

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The question here is how to write code to assing user to a project with has and belongs to many association? — Mirza Memic, Jun 27 '16 at 02:39

score 1 · Answer 1 · answered Jun 27 '16 at 10:00

I definitely must recommend you to not use has_and_belongs_to_many, because there is no way for you do to callbacks, validations and so on.

It is definitely nice to use a real join model and use has_many, through.

class User
  has_many :project_users, dependent: :destroy
  has_many :projects, through: :project_users
end

class Project
  has_many :project_users, dependent: :destroy
  has_many :users, through: :project_users
end

class ProjectUser
  belongs_to :project, required: true
  belongs_to :user, required: true

  validates :project, uniqueness: { scope: :user }
end

This works very seamlessly, you can do:

User.update(project_ids: [1,5,6,7])

And it will join the user to these project unless any validations fail.

I started out a big project with these tables everywhere, after a few months we started running into duplication issues, bad state of records and it was a hot mess. Using a real join model is so worth it.

Thank you for the tip! Ill be sure to keep that in mind! – Jon Cho Jun 27 '16 at 20:24 — Jon Cho, Jun 27 '16 at 20:24

score 0 · Answer 2 · answered Jun 27 '16 at 02:47

Since you have your project ID inside hidden you could just do this inside JOIN (post) action

def join
  @project = Project.find(params[:project][:id])
  current_user.projects << @project
end

so if you have instance of @project and instance of user - in my example it is current_user( for example if you use devise) then you would just assign them using operator <<

Here is the reference:

http://guides.rubyonrails.org/association_basics.html#has-many-association-reference

Hope it helps

Thanks for responding. How would i then display the users that clicked join into the group? — Jon Cho, Jun 27 '16 at 03:02

Rails 4 - has_and_belongs_to_many assocation

2 Answers2