Most performant way to load associations in rails-CodePudding

I'm trying to load a nested association, a User can belong to many Groups and I want to load all Posts from Groups where the user is a member, but only the posts no the groups as well.

Something like current_user.groups.eager_load(:posts), but without nesting posts under groups.

CodePudding user response：

I'm assuming Post belongs to Group here.

Start with the model that you need to load and build the query from there. If user belongs to 2 groups here, this will load all the posts from those 2 groups.

Post.where(group: current_user.groups)

CodePudding user response：

You can set up a shortcut from User to Post with has_many :through

class User < ApplicationRecord
  has_and_belongs_to_many :groups
  has_many :posts, through: :groups

  # if User already has a `has_many :posts`, you'll need 
  # to give the through-association a unique name like this:
  # has_many :group_posts, through: :groups, source: :posts
end

class Group < ApplicationRecord
  has_and_belongs_to_many :users
  has_many :posts
end

class Post < ApplicationRecord
  belongs_to :group

  # optionally, you can define the inverse here as well
  # has_many :users, through: :group
end
...

# eager_load on a query: User.includes(:posts) or User.eager_load(:posts)
# get from current user: current_user.posts