在Rails 3.2.11中引发多个联接的不明确错误

Question

我有一个查询：

User.select("distinct username as value, username as foto, roles.user_id as ID, 
followers as follower ").
where("username ILIKE ?", "%#{params[:term]}%").
joins(:identities).joins(:roles).all(conditions:{roles:{name: 'Creator'}})

但是user_id得到了一个错误，因为我认为identities表也在使用它。

如何实际指定user_id列仅用于查询roles表？

任何变通办法都将不胜感激。

编辑：

日志：

Rendered campaigns/_campaign_new.html.haml (27.7ms)
  User Load (1.1ms)  SELECT distinct username as value, user_id as ID, username as foto FROM "users" INNER JOIN "roles_users" ON "roles_users"."user_id" = "users"."id" INNER JOIN "roles" ON "roles"."id" = "roles_users"."role_id" WHERE "roles"."name" = 'Creator' AND (username ILIKE '%%')
  User Load (1.9ms)  SELECT distinct username as value, username as foto, user_id as ID, followers as follower FROM "users" INNER JOIN "identities" ON "identities"."user_id" = "users"."id" INNER JOIN "roles_users" ON "roles_users"."user_id" = "users"."id" INNER JOIN "roles" ON "roles"."id" = "roles_users"."role_id" WHERE "roles"."name" = 'Creator' AND (username ILIKE '%%')
PG::AmbiguousColumn: ERROR:  column reference "user_id" is ambiguous
LINE 1: ...ECT distinct username as value, username as foto, user_id as...
                                                             ^
: SELECT distinct username as value, username as foto, user_id as ID, followers as follower  FROM "users" INNER JOIN "identities" ON "identities"."user_id" = "users"."id" INNER JOIN "roles_users" ON "roles_users"."user_id" = "users"."id" INNER JOIN "roles" ON "roles"."id" = "roles_users"."role_id" WHERE "roles"."name" = 'Creator' AND (username ILIKE '%%')
  Rendered campaigns/new.js.erb (38.3ms)
Completed 500 Internal Server Error in 51ms
ActiveRecord::StatementInvalid - PG::AmbiguousColumn: ERROR:  column reference "user_id" is ambiguous
LINE 1: ...ECT distinct username as value, username as foto, user_id as...
                                                             ^
: SELECT distinct username as value, username as foto, user_id as ID, followers as follower  FROM "users" INNER JOIN "identities" ON "identities"."user_id" = "users"."id" INNER JOIN "roles_users" ON "roles_users"."user_id" = "users"."id" INNER JOIN "roles" ON "roles"."id" = "roles_users"."role_id" WHERE "roles"."name" = 'Creator' AND (username ILIKE '%%'):

Answer 1

您应该能够使用users.id或roles_users.user_id:

User.select("distinct username as value, username as foto, users.id as ID ...