问题描述
我有 users 和 projects 的集合.每个项目都完全连接到一个用户.
I have collections of users and projects.Every project is connected exactly to one user.
我的问题是:每个用户都应持有项目ID列表吗?
My question is: should every user hold the list of project ids?
如果我要检索特定用户的所有项目，则该选项更有效和最佳实践:
If i want to retrieve all the projects of a specific user, which option is more efficient and best practice:
- 在用户ID属性的项目集合上创建索引.不仅仅是查询用户ID属性.
- 在项目ID属性的项目集合上创建索引.相比之下，如果用户持有其项目ID，则只需查询那些特定ID的项目集合即可.
选择哪个选项?也许还有第三种更好的选择?第一种选择的优点是，删除/添加项目时，我不需要更新用户文档中的项目列表.
Which option to choose? Maybe there is a third option that is better?The advantage of the first option, is that i don't need to update the list of project in the user document when deleting/adding projects.
谢谢！
推荐答案
一个用户可以有多个 projects (并且一个项目仅与一个用户相关联).这是一对多关系.
A user can have many projects (and a project is associated with one user only). This is a one-to-many relationship.
每个用户应该存储他/她的项目的列表.例如:
Every user should store the list of his/her projects. For example:
user:
id: <some value>,
name: <some value>,
email: <some value>,
projects: [
{ projectId: <some value>, projectName: <...>, projectDescription: <....>, otherInfo: { fld1: <...>, fld2: <...>, etc. } },
{ projectId: <some value>, projectName: <...>, projectDescription: <....>, otherInfo: { fld1: <...>, fld2: <...>, etc. } },
...
]
请注意，每个 project 是 projects 数组中的一个子文档(对象或嵌入式文档). project 具有其相关的详细信息，例如 projectId ， projectName 等.
Note that each project is a sub-document (object or embedded document) within the projects array. A project has its related details like, projectId, projectName, etc..
a.在用户id属性上的项目集合上创建索引.不仅仅是查询用户ID属性.
a. Create an index on projects collection on the user id property. than just query on user id property.
b.在项目id属性上的项目集合上创建索引.比方说，如果用户持有其项目ID，则只需查询项目这些特定ID的集合.
b. Create an index on project collection on the project id property. than, if the user holds its project ids, just query projects collection for those specific ids.
我认为，应该只有一个集合被称为 user_projects .假设:(i)一个 user 可能有0到100个项目，并且(ii)一个 project 的详细信息不是太大.
I think, there should be only one collection called as user_projects. Assuming that: (i) a user may have 0 to 100 projects, and (ii) a project's details are not too huge.
这是将1-to-N关系的许多"面嵌入一个"面的模型.这是推荐的方式，可以对数据进行非规范化.这具有高效和快速查询的优势.这样简化了事务，因为只需对同一集合中的文档进行一次操作即可进行写入(插入，更新和删除).
This is a model of embedding the 'many' side of the 1-to-N relationship into the 'one' side. This a recommended way, de-normalizing the data. This has the advantage of efficient and fast queries. This simplifies transactions, as writes (inserts, updates and deletes) are going to be atomic with single operation to a document within the same collection.
您将使用 user id 或 name (具有唯一索引)来检索文档，这将非常快询问.您可以在 projects 数组上具有索引(数组字段上的索引称为 Multikey Indexes )-在项目的字段上.例如，在 projectId 或/和 projectName 上进行索引是有意义的.
You will be using the user id or name (with a unique index) to retrieve a document, and it will be very fast query. You can have index on the projects array (indexes on array fields are called as Multikey Indexes) - on the project's fields. For example, index on projectId or/and projectName makes sense.
您可以获取用户的所有项目-使用 user id / name 的简单查询.查询 projection 允许显示与 project 相关的信息.您可以使用 find 或 aggregate 方法来构建查询.您可以使用 projectId 或 projectName 向特定的 project 查询一个 user .由于在 user 和 project 字段上都有索引，因此这将是一种高效的查询.
You can get all projects for a user - its a simple query using the user id / name. Query projection allows what information related to project is displayed. You can use a find or aggregate method to build the query.You can query a specific project for a user, using the projectId or projectName. Since there are indexes on user and project fields, this will be an efficient query.
因此，我的建议是有一个单一集合 user_projects ，其中包含 user 的信息和 project 信息
So, my recommendation is to have a single collection, user_projects, with a user's information and the projects information embedded in it.
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