Rails Eager 加载（包含）和 where 子句不起作用？

Question

我正在使用 Rails 4.1 和我的模型，例如：

Client has_many TicketLists
TicketList has many projects

现在我正在尝试在客户端模型中使用急切加载，例如：

class Client < ActiveRecord::Base
  def ticket_lists_with_project_id(project_id)
    ticket_lists.includes(:projects).where("projects.id = ?", project_id)
  end  
end  

当我这样做时：

Client.find(2).ticket_lists_with_project_id(1)
  Client Load (1.7ms)  SELECT  "clients".* FROM "clients"  WHERE "clients"."is_destroyed" = 'f' AND "clients"."is_closed" = 'f' AND "clients"."id" = $1 LIMIT 1  [["id", 2]]
PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "projects"
LINE 1: ...d" = 'f' AND "ticket_lists"."client_id" = $1 AND (projects.i...
                                                             ^
: SELECT "ticket_lists".* FROM "ticket_lists"  WHERE "ticket_lists"."is_destroyed" = 'f' AND "ticket_lists"."client_id" = $1 AND (projects.id = 1)
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "projects"
LINE 1: ...d" = 'f' AND "ticket_lists"."client_id" = $1 AND (projects.i...

Answer 1

试试下面的：

class Client < ActiveRecord::Base
  def ticket_lists_with_project_id(project_id)
    ticket_lists.includes(:projects)
                .where("projects.id = ?", project_id)
                .references(:projects)
  end  
end

它会起作用的。如果你想 add conditions 到你包含的模型，你必须明确引用它们。另外注意includes 使用关联名称，而references 需要实际的表名。

Answer 2

而不是这个：

ticket_lists.includes(:projects).where("projects.id = ?", project_id)

这样做：

ticket_lists.joins(:projects).where("projects.id = ?", project_id)

由于你使用的是 Rails 4，你可以让它看起来更可爱：

ticket_lists.joins(:projects).where(projects: {id: project_id})

Answer 3

这可能会对您有所帮助：

Client.includes(:ticket_lists => :projects).where("clients.id = ? ", 2)

或

class Client < ActiveRecord::Base
  def ticket_lists_with_project_id(project_id)
    Client.includes(:ticket_lists => :projects).where("projects.id = ?", project_id)
  end  
end