通过Mongoid/MongoDB进行多对多建模 [英] Modeling many-to-many :through with Mongoid/MongoDB

问题描述

我对Mongoid/MongoDB相对较新，我对如何建模特定的多对多关系有疑问.

I'm relatively new to Mongoid/MongoDB and I have a question about how to model a specific many-to-many relationship.

我有一个User模型和一个Project模型.用户可以属于多个项目，并且每个项目成员资格都包含一个角色(例如，管理员"，编辑者"或查看者").如果我使用的是ActiveRecord，则可以使用has_many :through在User和Project之间建立多对多关联，然后在联接表中放置一个角色字段.

I have a User model and a Project model. Users can belong to many projects, and each project membership includes one role (eg. "administrator", "editor", or "viewer"). If I were using ActiveRecord then I'd set up a many-to-many association between User and Project using has_many :through and then I'd put a field for role in the join table.

在MongoDB中对此场景进行建模的好方法是什么，我如何用Mongoid声明该模型?下面的示例似乎是对此建模的一种好方法，但是我不知道如何用Mongoid优雅地声明User与嵌入的ProjectMembership之间的关系.

What is a good way to model this scenario in MongoDB and how would I declare that model with Mongoid? The example below seems like a good way to model this, but I don't know how to elegantly declare the relational association between User and the embedded ProjectMembership with Mongoid.

提前谢谢！

db.projects.insert(
  { 
    "name" : "Test project",
    "memberships" : [
      {
        "user_id" : ObjectId("4d730fcfcedc351d67000002"),
        "role" : "administrator"
      },
      {
        "role" : "editor",
        "user_id" : ObjectId("4d731fe3cedc351fa7000002")
      }
    ]
  }
)

db.projects.ensureIndex({"memberships.user_id": 1})

推荐答案

对一个好的Mongodb模式进行建模实际上取决于您如何访问数据.在上述情况下，您将为您的memberships.user_id索引编制索引，这看起来不错.但是，随着您添加查看器，编辑器和管理员，您的文档大小也会增加.另外，您的架构将使查询这样的查询变得困难:

Modeling a good Mongodb schema really depends on how you access your data. In your described case, you will index your memberships.user_id key which seems ok. But your document size will grow as you will add viewers, editors and administrators. Also, your schema will make it difficult to make querys like:

查询项目，其中user_id xxx是编辑者:

Query projects, where user_id xxx is editor:

同样，您可能不需要查询这样的项目，因此您的架构看起来不错.但是，如果您需要通过user_id AND角色查询项目，我建议您创建一个'project_membership'集合:

Again, you maybe do not need to query projects like this, so your schema looks fine. But if you need to query your projects by user_id AND role, i would recommend you creating a 'project_membership' collection :

db.project_memberships.insert(
  { 
    "project_id" : ObjectId("4d730fcfcedc351d67000032"),
    "editors" : [
      ObjectId("4d730fcfcedc351d67000002"),
      ObjectId("4d730fcfcedc351d67000004")
    ],
    "viewers" : [
      ObjectId("4d730fcfcedc351d67000002"),
      ObjectId("4d730fcfcedc351d67000004"),
      ObjectId("4d730fcfcedc351d67000001"),
      ObjectId("4d730fcfcedc351d67000005")
    ],
    "administrator" : [
      ObjectId("4d730fcfcedc351d67000011"),
      ObjectId("4d730fcfcedc351d67000012")
    ]
  }
)

db.project_memberships.ensureIndex({"editors": 1})
db.project_memberships.ensureIndex({"viewers": 1})
db.project_memberships.ensureIndex({"administrator": 1})

甚至更容易...在您的项目模式上添加索引:

Or even easier... add an index on your project schema:

db.projects.ensureIndex({"memberships.role": 1})

这篇关于通过Mongoid/MongoDB进行多对多建模的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！