使用 Rails 关联查找所有管理员

Question

How do I find all admins using Rails 6 active record associations?

I have the following classes:

class Group < ApplicationRecord
  has_many :relationships, dependent: :destroy
  has_many :users, through: :relationships
end

class User < ApplicationRecord
  has_many :posts, dependent: :destroy
  has_many :relationships, dependent: :destroy
  has_many :groups, through: :relationships
end

class Relationship < ApplicationRecord
  belongs_to :user
  belongs_to :group
  validates :user_id, presence: true
  validates :group_id, presence: true
  validates :admin, inclusion: [true, false]

I'd like to add admins as a has_many relationship in Group. Here's my first attempt at doing so:

has_many :admins, class_name: "User", through: :relationships

How would I filter those users whose relationship to the group has the admin attribute set to true?

Answer 1

Associations can be scoped using the normal query syntax.

class Group < ApplicationRecord
  ...

  has_many :admins,
    -> { where({ relationships: { admin: true} }) },
    through: :relationships,
    source: :user
end

source is necessary because otherwise it will try to do the has_many through Relationships.admins .

group.admins is equivalent to group.users.where({ relationships: { admin: true} }) .

Answer 2

You could've modified your Group model to something like:

class Group < ApplicationRecord
  scope :admins, -> { where(relationships: { admin: true }) }

  has_many :relationships, dependent: :destroy
  has_many :users, through: :relationships
end

From it you can use Group.joins(:users).admins to get groups with assoiciated admins.