MongoDB-手册参考示例 [英] MongoDB - manual references example

问题描述

我正在阅读手册参考部分. MongoDB数据库参考文档，但是我真的不理解第二次查询来解析参考字段"的部分.您能给我一个这个查询的例子吗，这样我就可以更好地了解他们在说什么.

I was reading the manual references part from the MongoDB Database References documentation, but I don't really understand the part of the "second query to resolve the referenced fields". Could you give me an example of this query, so i can get a better idea of what they are talking about.

手动引用是指将一个文档的_id字段包含在另一文档中的实践.然后，应用程序可以根据需要发出第二个查询来解析引用的字段."

"Manual references refers to the practice of including one document’s _id field in another document. The application can then issue a second query to resolve the referenced fields as needed."

推荐答案

在您所指的手册部分中，该文档非常清晰，其中

The documentation is pretty clear in the manual section you are referring to which is the section on Database References. The most important part in comprehending this is contained in the opening statement on the page:

"MongoDB不支持联接.在MongoDB中，某些数据被非规范化，或与相关数据一起存储在文档中以消除对联接的需要.但是，在某些情况下，将相关信息存储在单独的文档中是有意义的，通常在不同的文档中集合或数据库."

"MongoDB does not support joins. In MongoDB some data is denormalized, or stored with related data in documents to remove the need for joins. However, in some cases it makes sense to store related information in separate documents, typically in different collections or databases."

更多信息涵盖了您如何可能选择处理存储在另一个集合中的数据的主题.

The further information covers the topic of how you might choose to deal with accessing data that you store in another collection.

有 DBRef 可以在某些驱动程序中实现规范()，而无需过多详细说明，因此可以在您的文档中找到这些规范时自动将引用的文档检索(展开)到当前文档中.这将在幕后"中实现，并对该集合中的_id文档进行另一个查询.

There is the DBRef specification which without going into too much more detail, may be implemented in some drivers as a way that when these are found in your documents they will automatically retrieve (expand) the referenced document into the current document. This would be implemented "behind the scenes" with another query to that collection for the document of that _id.

对于 手册参考 这基本上是说文档中只有一个字段，该字段的内容来自另一个文档的 ObjectId .这仅与DBRef不同，因为基本驱动程序实现将从不进行处理，这将使您可以自行处理其他文档的进一步检索.

In the case of Manual References this is basically saying that there is merely a field in your document that has as it's content the ObjectId from another document. This only differs from the DBRef as something that will never be processed by a base driver implementation is leaves how you handle any further retrieval of that other document soley up to you.

在以下情况下:

> db.collection.findOne()

{
   _id: <ObjectId>,
   name: "This",
   something: "Else",
   ref: <AnotherObjectId>
}

文档中的ref字段只不过是一个普通的ObjectId，并且没有什么特别的.这允许您执行的操作是提交自己的查询以获取所引用的对象详细信息:

The ref field in the document is nothing more than a plain ObjectId and does nothing special. What this allows you to do is submit your own query to get the Object details this refers to:

> db.othercollection.findOne({ _id: <AnotherObjectId > })
{
  _id: <ObjectId>
  name: "That"
  something: "I am a sub-document to This!"
}

请记住，所有这些过程都是通过驱动程序API在客户端进行的.在任何情况下，获取其他文档的任何操作均不会在服务器上发生.

Keep in mind that all of this processes on the client side via the driver API. None of this fetching other documents happens on the server in any case.

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