轨道mongoid标准由协会找到 [英] rails mongoid criteria find by association

问题描述

我试图找到它包含在一个belongs_to的关系相关联的用户名的记录，但它不工作。

I'm trying to find a record by associated username which is included in a belongs_to relation, but it's not working.

文章属于用户
用户有很多的文章

Articles belong to Users Users have many articles

Article.where（USER_ID：someid）工作正常，但我想使用的用户名是存储在用户表参照

Article.where(user_id: someid) works fine, but I'd like to use the username as reference which is stored in the Users table.

Article.includes(:user).where(:username => "erebus")
Article.includes(:user).where("user.username" => "erebus")

我也有 identity_map_enabled：真正的

Article.includes（：用户）.inclusions 返回的关系细节

不工作，那我不理解？

推荐答案

您必须记住，有MongoDB中没有加入。在关系DBS，包括形成连接查询，你可以从无论是在查询中的表使用的列。然而，由于缺少连接在mongodb的，同样是不可能的。

You have to keep in mind that there are no joins in mongodb. In relational dbs, includes forms a join query and you can use columns from both the tables in query. However due to absence of joins in mongodb, same is not possible.

在mongoid，包括只是保存了一堆数据库调用。它获取并存储身份地图快速检索相关的记录，但还是在查询时，一个查询只能处理一个集合。

In mongoid, includes just saves a bunch of db calls. It fetches and stores the associated records in identity map for fast retrieval, but still while querying, one query can only deal with one collection.

如果您需要根据用户名的文章，我建议以下解决方法：

If you need articles based on user names, I would suggest following work around:

user_ids = User.where(username: 'erebus').only(:_id).map(&:_id)
articles = Article.where(:user_id.in => user_ids)

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