How to write ActiveRecord when there are several associations?

Question

Models are as follows:

class Contract < ActiveRecord::Base  
  belongs_to :buyer, :class_name => 'Customer', :foreign_key => 'buyer_customer_id' 
  belongs_to :user, :class_name => 'Customer', :foreign_key => 'user_customer_id'
  belongs_to :currency
end  

class Customer < ActiveRecord::Base  
  has_many :as_buyer_in_contracts, :class_name => 'Contract', :foreign_key => 'buyer_customer_id'  
  has_many :as_user_in_contracts, :class_name => 'Contract',:foreign_key => 'user_customer_id'  
end

class Currency < ActiveRecord::Base
  has_many :contracts
end

And below is the data:

Contract
+----+-------------------+------------------+-------------+
| id | buyer_customer_id | user_customer_id | currency_id |
+----+-------------------+------------------+-------------+
|  1 |         1         |        3         |      3      |
|  2 |         2         |        2         |      2      |
|  3 |         2         |        1         |      2      |
|    |                   |                  |             |


Customer
+----+-------------------+
| id |       name        |
+----+-------------------+
|  1 |    Terry Brown    |
|  2 |    Tom Green      |
|  3 |    Kate White     |
|    |                   |

Currency
+----+-------------------+
| id |       name        |
+----+-------------------+
|  1 |        EUR        |
|  2 |        USD        |
|  3 |        JPY        |
|    |                   |

And now I want to find all the contracts signed with the client under the name "Terry", for example:

Contract.where("customers.name like '%Terry%'").includes(:buyer,:user)
#I want 1 and 3, but it can only get 1
Contract.where("customers.name like '%Terry%'").includes(:user, :buyer)
#If I write "user" before "buyer", then I can only get 3

Someone told me that it can work as follows:

Contract.join(:customer).where("customers.name like '%terry%'").includes(:user,:buyer)
#It works fine.

I tried and it works. But if the model of the Contract belongs to another model, for example currency_id, the method above cannot work again.

Contract.join(:customer).where("customers.name like '%terry%'").includes(:currency, :user, :buyer)
#>>Mysql2::Error: Unknown column 'customers_contracts.id' in 'field list': ...

Answer 1

This is because you should not use unions in conjunction with included ones. It is not sufficiently accented (and there is no warning in the rails), but

select, join, group, has, etc. DOES NOT WORK! Includes!

, . , , .

, ...

activerecord >= 3.0 ( ), squeel gem. .

( squeel):

Contract.joins{buyer.outer}.joins{user.outer}.where("name like '%terry%'")

, , : ...

Answer 2

: : : ?

: /

Contract.join(:buyer).where("customers.name like '%terry%'").includes(:currency, :user, :buyer)

, -

Contract.join("INNER JOIN customers ON customers.id = contracts.buyer_customer_id").where("customers.name like '%terry%'").includes(:currency, :user, :buyer)

, , sql - log/development.log