has_and_belongs_to_many or has_many :through?

As you may (or may not) know, there are two ways to build a many-to-many (or N-N) relationship with Rails.

  1. The first way uses has_and_belongs_to_many in both models. You’ll have to create a join table that has no corresponding model or primary key. ( ActiveRecord will look by default for a join table called groups_users )

class Group < ActiveRecord::Base has_and_belongs_to_many :users # foreign keys in the join table end class User < ActiveRecord::Base has_and_belongs_to_many :groups # foreign keys in the join table end

The join table can have more attributes which can be filled with the <span style="font-style: italic;">push_with_attributes</span> method:

<code>class User &lt; ActiveRecord::Base has_and_belongs_to_many :groups # foreign keys in the join table

def join_group(group) groups.push_with_attributes(group, :joined_at =&gt; Time.now) end end2. The second way uses a has_many association with the :through option and a join model:
class Subscriptions &lt; ActiveRecord::Base belongs_to :group # foreign key - programmer_id belongs_to :user # foreign key - project_id end class Group :subscriptions end class User :subscriptions end
`If you have to work with the relationship model as its own entity, thent you’ll need to use has_many :through. Otherwise, you can just stick to has_and_belongs_to_many.

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