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Create a Compound Unique Index创建复合唯一索引

You enforce a unique constraint on compound indexes. A unique compound index enforces uniqueness on the combination of the index key values.您对a href="/v8.3/core/indexes/index-types/index-compound/#std-label-index-type-compound">复合索引实施了唯一的约束。唯一复合索引强制索引键值组合的唯一性。

To create a unique index in the MongoDB Shell, use the db.collection.createIndex() method with the unique option set to true.要在MongoDB Shell中创建唯一索引，请使用db.collection.createIndex()方法，并将unique选项设置为true。

db.collection.createIndex(
   {
      <field1>: <sortOrder>,
      <field2>: <sortOrder>,
      ...
      <fieldN>: <sortOrder>
   },
   { unique: true }
 )

About this Task关于此任务

This example adds a unique compound index on the groupNumber, lastname, and firstname fields of a members collection. The index ensures that the combination of these field values is unique for each document in the collection.此示例在成员集合的groupNumber、lastname和firstname字段上添加了一个唯一的复合索引。索引确保这些字段值的组合对于集合中的每个文档都是唯一的。

Steps步骤

To create a unique index on groupNumber, lastname, and firstname fields of the members collection, run the following command in mongosh:要在成员集合的groupNumber、lastname和firstname字段上创建唯一索引，请在mongosh中运行以下命令：

db.members.createIndex(
   { groupNumber: 1, lastname: 1, firstname: 1 },
   { unique: true }
)

The created index enforces uniqueness for the combination of groupNumber, lastname, and firstname values.创建的索引强制groupNumber、lastname和firstname值的组合具有唯一性。

Compound Unique Indexes on Fields with Embedded Arrays具有嵌入式数组的字段上的复合唯一索引

Consider a collection with the following document:考虑一个包含以下文档的集合：

db.myColl.insertOne(
   { _id: 1, a: [ { loc: "A", qty: 5 }, { qty: 10 } ] }
)

Create a unique compound multikey index on a.loc and a.qty:在a.loc和a.qty上创建一个唯一的复合多键索引：

db.myColl.createIndex( { "a.loc": 1, "a.qty": 1 }, { unique: true } )

The unique index permits the insertion of the following documents into the collection since the index enforces uniqueness for the combination of a.loc and a.qty values:唯一索引允许将以下文档插入到集合中，因为该索引强制执行a.loc和a.qty值组合的唯一性：

db.myColl.insertMany( [
   { _id: 2, a: [ { loc: "A" }, { qty: 5 } ] },
   { _id: 3, a: [ { loc: "A", qty: 10 } ] }
] )

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