MongoDB复合键 [英] MongoDB Composite Key

问题描述

我刚刚开始使用MongoDb，我注意到我获得了许多重复记录，我认为这些记录是独一无二的。我想知道如何为我的数据使用复合键，我正在寻找有关如何创建它们的信息。最后，我使用Java来访问mongo和morphia作为我的ORM层，所以在你的答案中包括那些将是很棒的。

I'm just getting started with MongoDb and I've noticed that I get a lot of duplicate records for entries that I meant to be unique. I would like to know how to use a composite key for my data and I'm looking for information on how to create them. Lastly, I am using Java to access mongo and morphia as my ORM layer so including those in your answers would be awesome.

Morphia： http://code.google.com/p/morphia/

推荐答案

您也可以将对象用于_id字段。 _id字段始终是唯一的。这样你就得到了一个复合主键：

You can use objects for the _id field as well. The _id field is always unique. That way you kind of get a composite primary key:

 { _id : { a : 1, b: 1} }

创建这些ID时要小心，键的顺序（示例中的a和b）很重要，如果你交换它们，它被认为是一个不同的对象。

Just be careful when creating these ids that the order of keys (a and b in the example) matters, if you swap them around, it is considered a different object.

另一种可能性是单独留下_id和创建一个独特的复合索引。

The other possibility is to leave _id alone and create a unique compound index.

db.things.ensureIndex({firstname: 1, lastname: 1}, {unique: true});
//Deprecated since version 3.0.0, is now an alias for db.things.createIndex()

https://docs.mongodb.org/ v3.0 / reference / method / db.collection.ensureIndex /

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