Has And Belongs To Many ​

The HasAndBelongsToMany association works similarly to HasMany.

field :users, as: :has_and_belongs_to_many

Options ​

-> searchable

class Avo::Resources::CourseLink < Avo::BaseResource
  def fields
    field :links,
      as: :has_many,
      searchable: true
  end
end

# app/avo/resources/course_link.rb
class Avo::Resources::CourseLink < Avo::BaseResource
  self.search = {
    query: -> {
      query.ransack(id_eq: params[:q], link_cont: params[:q], m: "or").result(distinct: false)
    }
  }
end

-> attach_scope

field :user,
  as: :belongs_to,
  attach_scope: -> { query.non_admins }

-> scope

field :user,
  as: :belongs_to,
  scope: -> { query.approved }

-> description

-> use_resource

-> discreet_pagination

-> hide_search_input

Search query scope ​

If the resource used for the has_many association has the search block configured with a query, Avo will use that to scope out the search query to that association.

For example, if you have a Team model that has_many Users, now you'll be able to search through that team's users instead of all of them.

You can target that search using params[:via_association]. When the value of params[:via_association] is has_many, the search has been mad inside a has_many association.

For example, if you want to show the records in a different order, you can do this:

self.search = {
  query: -> {
    if params[:via_association] == 'has_many'
      query.ransack(id_eq: params[:q], m: "or").result(distinct: false).order(name: :asc)
    else
      query.ransack(id_eq: params[:q], m: "or").result(distinct: false)
    end
  }
}

Show on edit screens ​

By default, has_and_belongs_to_many is only visible on the Show page. If you want to enable it on the Edit page, too, you need to add the show_on: :edit option.

You may use the redirect helpers to have the following flow:

1. User is on the New view. They can't see the association panels yet.
2. User creates the record.
3. They get redirected to the Show/Edit view, where they can see the association panels.
4. User attaches associations.

Searchable has_and_belongs_to_many ​

Similar to belongs_to, the has_many associations support the searchable option.

Add scopes to associations ​

When displaying has_many associations, you might want to scope out some associated records. For example, a user might have multiple comments, but on the user's Show page, you don't want to display all the comments, but only the approved ones.

# app/models/comment.rb
class Comment < ApplicationRecord
  belongs_to :user, optional: true

  scope :approved, -> { where(approved: true) }
end

# app/models/user.rb
class User < ApplicationRecord
  has_many :comments
end

# app/avo/resources/user.rb
class Avo::Resources::User < Avo::BaseResource
  def fields
    field :comments, as: :has_many, scope: -> { query.approved }
  end
end

The comments query on the user Index page will have the approved scope attached.

With version 2.5.0, you'll also have access to the parent record so that you can use that to scope your associated models even better.

All the has_many associations have the attach_scope option available too.

Show/hide buttons ​

You will want to control the visibility of the attach/detach/create/destroy/actions buttons visible throughout your app. You can use the policy methods to do that.

Find out more on the authorization page.