Rails 4 Reflexive Many-to-Many Association - ruby-on-rails-4

Question

I'm implementing a Rails 4 app that has a Reflexive Many-to-Many Association to represent some MailChimp and HelpScout API parameters.
Some of those parameters have child parameters. Thus, those child parameters have parent parameters (otherwise they couldn't be a child, right?! ;D ).
To implement the reflexive association the two tables below were created
create_table "api_params", force: true do |t|
t.string "name"
t.string "description"
t.string "type"
t.boolean "required"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "nested_params", force: true do |t|
t.integer "parent_param_id"
t.integer "child_param_id"
t.boolean "required"
t.datetime "created_at"
t.datetime "updated_at"
end
add_index "nested_params", ["child_param_id"], name: "index_nested_params_on_child_param_id"
add_index "nested_params", ["parent_param_id"], name: "index_nested_params_on_parent_param_id"
What I'd like to have are two methods. One to retrieve a database record's parents and another one to retrieve its children. Below I show you an example.
apiParam = ApiParam.first # retrieving any database record
apiParam.parent_params
# => returns a set of apiParam's parents
apiParam.child_params
# => returns a set of apiParam's children
I read all day long about associations but the examples are always the same. I mean, there is always a class where you define a has_many through and another one where you define a belongs_to but it wasn't enough for what I need.
Thanks in advance. I appreciate any kind of help.

Answer 1

I have your solution (in my case I have the model SyncType):
class SyncType < ActiveRecord::Base
has_and_belongs_to_many(:parents,
:class_name => "SyncType",
:join_table => "sync_type_parents",
:foreign_key => "sync_type_id",
:association_foreign_key => "sync_type_parent_id")
has_and_belongs_to_many(:children,
:class_name => "SyncType",
:join_table => "sync_type_parents",
:foreign_key => "sync_type_parent_id",
:association_foreign_key => "sync_type_id")
end
migration:
create_table "sync_type_parents", :force => true, :id => false do |t|
t.integer "sync_type_id", :null => false
t.integer "sync_type_parent_id", :null => false
end
Enjoy! ;)

Answer 2

I found the answer and I hope it can be helpful for everyone with same kind of problem.
In short, I've got the answer from Ryan Bates' railscasts.com website. More specificly, the answer were found here.
My classes are now as follow:
class NestedParam < ActiveRecord::Base
belongs_to :api_param
belongs_to :child_param, class_name: 'ApiParam'
end
class ApiParam < ActiveRecord::Base
has_many :nested_params
has_many :child_params, :through => :nested_params
has_many :parent_api_params, :class_name => "NestedParam", :foreign_key => "child_param_id"
has_many :parent_params, :through => :parent_api_params, :source => :api_param
end
ActiveRecord::Schema.define(version: 20140910175658) do
create_table "api_params", force: true do |t|
t.string "name"
t.string "description"
t.boolean "required", default: true
t.boolean "struct", default: false
t.string "type"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "nested_params", force: true do |t|
t.integer "api_param_id"
t.integer "child_param_id"
t.boolean "required"
t.datetime "created_at"
t.datetime "updated_at"
end
add_index "nested_params", ["api_param_id"], name: "index_nested_params_on_api_param_id"
add_index "nested_params", ["child_param_id"], name: "index_nested_params_on_child_param_id"
end