Rails Engines - is it possible to add associations to the model in a container model like Forem does -

this question more single question breaking more managable pieces: rails engines - simple possible engine (1) add model , (2) add association in containing class

i testing out building rails engine , curious whether can add association specific model in hosting / container app.

the hosting app has user model class (yes, never chnage) , engine called abc , have model in engine called posts (so abc::post , table abc_posts). i'd add user class in main app association. drop dead simple try, created in engine:

#located in engine at: abc/app/models/user.rb  class user < activerecord::base   has_many :abc_posts end 

the post file:

#located in engine at: abc/app/models/abc/post.rb module abc   class post < activerecord::base     attr_accessible :body, :header, :user_id     belongs_to :user   end end 

via rails console, able create records in table (easy part) user class doesn't know association. ideas on how done?

thx in advance

edit 1

i've tried using decorators gem used in forem (see comment below) , have file:

#abc/app/decorators/lib/abc/user_class_decorator.rb object.const_get(user).class_eval   has_many :abc_posts, :class_name => "abc::post", :foreign_key => "user_id" end 

i have included decorators via: lib/abc.rb

require "decorators" 

but doesn't seem working. not sure if right strategy or whether syntax correct.

that should job - specify class relationship:

class user < activerecord::base   has_many :posts, :class_name => "abc::post" end 

hmmm, created example , work ...

class parent < activerecord::base   has_many :children, :class_name => "abc::child" end 

the module class child in model/abc.

module abc   class child < activerecord::base     belongs_to :parent   end end 

here journal

1.9.3-p194 :001 > parent.create(:name => 'mr daddy') (0.1ms)  begin transaction sql (9.4ms)  insert "parents" ("created_at", "name", "updated_at") values (?, ?, ?)  [["created_at", fri, 03 may 2013 10:49:54 utc +00:00], ["name", "mr daddy"], ["updated_at", fri, 03 may 2013 10:49:54 utc +00:00]] (1.9ms)  commit transaction => #<parent id: 1, name: "mr daddy", created_at: "2013-05-03 10:49:54", updated_at: "2013-05-03 10:49:54">  1.9.3-p194 :002 > abc::child.create(:name => 'sammy boy', :parent => parent.first ) parent load (0.3ms)  select "parents".* "parents" order "parents"."id" asc limit 1 (0.1ms)  begin transaction sql (117.3ms)  insert "children" ("created_at", "name", "parent_id", "updated_at") values (?, ?, ?, ?)  [["created_at", fri, 03 may 2013 10:49:58 utc +00:00], ["name", "sammy boy"], ["parent_id", 1], ["updated_at", fri, 03 may 2013 10:49:58 utc +00:00]] (2.1ms)  commit transaction => #<abc::child id: 1, name: "sammy boy", parent_id: 1, created_at: "2013-05-03 10:49:58", updated_at: "2013-05-03 10:49:58">  1.9.3-p194 :003 > abc::child.create(:name => 'milly girl', :parent => parent.first ) parent load (0.3ms)  select "parents".* "parents" order "parents"."id" asc limit 1 (0.2ms)  begin transaction sql (0.8ms)  insert "children" ("created_at", "name", "parent_id", "updated_at") values (?, ?, ?, ?)  [["created_at", fri, 03 may 2013 10:50:15 utc +00:00], ["name", "milly girl"], ["parent_id", 1], ["updated_at", fri, 03 may 2013 10:50:15 utc +00:00]] (2.7ms)  commit transaction => #<abc::child id: 2, name: "milly girl", parent_id: 1, created_at: "2013-05-03 10:50:15", updated_at: "2013-05-03 10:50:15">  1.9.3-p194 :004 > parent.first.children.first parent load (0.4ms)  select "parents".* "parents" order "parents"."id" asc limit 1 abc::child load (0.3ms)  select "children".* "children" "children"."parent_id" = ? order "children"."id" asc limit 1  [["parent_id", 1]] => #<abc::child id: 1, name: "sammy boy", parent_id: 1, created_at: "2013-05-03 10:49:58", updated_at: "2013-05-03 10:49:58">  1.9.3-p194 :005 > parent.first.children.last parent load (0.5ms)  select "parents".* "parents" order "parents"."id" asc limit 1 abc::child load (0.4ms)  select "children".* "children" "children"."parent_id" = ? order "children"."id" desc limit 1  [["parent_id", 1]] => #<abc::child id: 2, name: "milly girl", parent_id: 1, created_at: "2013-05-03 10:50:15", updated_at: "2013-05-03 10:50:15">  1.9.3-p194 :006 > parent.first.children.count parent load (0.3ms)  select "parents".* "parents" order "parents"."id" asc limit 1 (0.3ms)  select count(*) "children" "children"."parent_id" = ?  [["parent_id", 1]] => 2