create

Command Fields命令字段

The create command has the following fields:create命令包含以下字段：

clusteredIndex: {
   key: { <string> },
   unique: <boolean>,
   name: <string>
}

changeStreamPreAndPostImages: {
   enabled: <boolean>
}

{ <storage-engine-name>: <options> }

{ <storage-engine-name>: <options> }

collation: {
   locale: <string>,
   caseLevel: <boolean>,
   caseFirst: <string>,
   strength: <int>,
   numericOrdering: <boolean>,
   alternate: <string>,
   maxVariable: <string>,
   backwards: <boolean>
}

encryptedFieldsConfig = {
    "fields": [
      {
        "keyId": UUID,                    // required
        "path": String,                   // path to field, required
        "bsonType": "string" | "int" ..., // required
        "queries":                        // optional
        [
          { "queryType": "equality" },
        ]
      }
    ],
    "queryPatterns": [                    // optional
       {"fieldName": queryType, "fieldName": queryType, … }
    ]
}

The db.createCollection() method and the db.createView() method wrap the create command.db.createCollection()方法和db.createView()方法包装create命令。

Resource Locking资源锁定

create obtains an exclusive lock on the specified collection or view for the duration of the operation. 在操作期间获取对指定集合或视图的独占锁定。All subsequent operations on the collection must wait until create releases the lock. 对集合的所有后续操作都必须等待create释放锁。create typically holds this lock for a short time.通常将该锁保持短时间。

Creating a view requires obtaining an additional exclusive lock on the system.views collection in the database. 创建视图需要对数据库中的system.views集合获取额外的独占锁。This lock blocks creation or modification of views in the database until the command completes.此锁会阻止在数据库中创建或修改视图，直到命令完成。

Transactions事务

Starting in MongoDB 4.4, you can create collections and indexes inside a multi-document transaction if the transaction is not a cross-shard write transaction.从MongoDB 4.4开始，如果多文档事务不是跨分片写入事务，则可以在该事务内创建集合和索引。

To use create in a transaction, the transaction must use read concern "local". 若要在事务中使用create，事务必须使用读取关注"local"。If you specify a read concern level other than "local", the transaction fails.如果指定了"local"以外的读取关注级别，则事务将失败。

Stable API

When using Stable API V1, you cannot specify the following fields in a create command:使用Stable API V1时，不能在创建命令中指定以下字段：

• autoIndexId
• capped
• indexOptionDefaults
• max
• size
• storageEngine

Create a Capped Collection创建封顶集合

To create a capped collection limited to 64 kilobytes, issue the command in the following form:要创建限制为64 KB的封顶集合，请按以下形式发出命令：

db.runCommand( { create: "collection", capped: true, size: 64 * 1024 } )

Create a Time Series Collection创建时间序列集合

To create a time series collection that captures weather data for the past 24 hours, issue this command:要创建捕捉过去24小时天气数据的时间序列集合，请发出以下命令：

db.createCollection(
    "weather24h",
    {
       timeseries: {
          timeField: "timestamp",
          metaField: "data",
          granularity: "hours"
       },
       expireAfterSeconds: 86400
    }
)

Alternately, to create the same collection but limit each bucket to timestamp values within the same hour, issue this command:或者，要创建相同的集合，但将每个桶限制为同一小时内的时间戳值，请发出以下命令：

db.createCollection(
    "weather24h",
    {
       timeseries: {
          timeField: "timestamp",
          metaField: "data",
          bucketMaxSpanSeconds: "3600",
          bucketRoundingSeconds: "3600"
       },
       expireAfterSeconds: 86400
    }
)

Create a Clustered Collection创建群集集合

The following create example adds a clustered collection named products:以下create示例添加了一个名为products的集群集合：

db.runCommand( {
   create: "products",
   clusteredIndex: { "key": { _id: 1 }, "unique": true, "name": "products clustered key" }
} )

In the example, clusteredIndex specifies:在示例中，clusteredIndex指定：

• "key": { _id: 1 }, which sets the clustered index key to the _id field.，将聚集索引键设置为_id字段。
• "unique": true, which indicates the clustered index key value must be unique.，表示聚集索引键值必须是唯一的。
• "name": "products clustered key", which sets the clustered index name.，用于设置聚集索引名称。

Create a Collection with Change Stream Pre- and Post-Images for Documents使用文档的更改流前后映像创建集合

Starting in MongoDB 6.0, you can use change stream events to output the version of a document before and after changes (the document pre- and post-images):从MongoDB 6.0开始，您可以使用更改流事件来输出更改前后文档的版本（文档前后映像）：

• The pre-image is the document before it was replaced, updated, or deleted. There is no pre-image for an inserted document.前映像是在文档被替换、更新或删除之前的文档。插入的文档没有前映像。
• The post-image is the document after it was inserted, replaced, or updated. There is no post-image for a deleted document.后映像是插入、替换或更新后的文档。已删除的文档没有后映像。
• Enable changeStreamPreAndPostImages for a collection using db.createCollection(), create, or collMod.使用db.createCollection()、create或collMod为集合启用changeStreamPreAndPostImages。

The following example creates a collection that has changeStreamPreAndPostImages enabled:以下示例创建启用了changeStreamPreAndPostImages的集合：

db.runCommand( {
   create: "temperatureSensor",
   changeStreamPreAndPostImages: { enabled: true }
} )

Pre- and post-images are not available for a change stream event if the images were:如果映像为以下情况，则前映像和后映像对更改流事件不可用：

• Not enabled on the collection at the time of a document update or delete operation.文档更新或删除操作时未在集合上启用。
• Removed after the pre- and post-image retention time set in expireAfterSeconds.在expireAfterSeconds中设置的前映和后映保留时间之后删除。
  • The following example sets expireAfterSeconds to 100 seconds:以下示例将expireAfterSeconds设置为100秒：

    use admin
    db.runCommand( {
       setClusterParameter:
          { changeStreamOptions: { preAndPostImages: { expireAfterSeconds: 100 } } }
    } )

  • The following example returns the current changeStreamOptions settings, including expireAfterSeconds:以下示例返回当前changeStreamOptions设置，包括expireAfterSeconds：

    db.adminCommand( { getClusterParameter: "changeStreamOptions" } )

  • Setting expireAfterSeconds to off uses the default retention policy: pre- and post-images are retained until the corresponding change stream events are removed from the oplog.将expireAfterSeconds设置为off使用默认的保留策略：保留前映像和后映像，直到从操作日志中删除相应的更改流事件。
  • If a change stream event is removed from the oplog, then the corresponding pre- and post-images are also deleted regardless of the expireAfterSeconds pre- and post-image retention time.如果更改流事件从操作日志中删除，则相应的前映像和后映像也将被删除，而不管映像前和后映像的保留时间是expireAfterSeconds。

Additional considerations:其他注意事项：

• Enabling pre- and post-images consumes storage space and adds processing time. Only enable pre- and post-images if you need them.启用前映和后映像会消耗存储空间并增加处理时间。只有在需要时才启用前映像和后映像。
• Limit the change stream event size to less than 16 megabytes. To limit the event size, you can:将更改流事件大小限制为小于16兆字节。要限制事件大小，您可以：
  • Limit the document size to 8 megabytes. 将文档大小限制为8兆字节。You can request pre- and post-images simultaneously in the change stream output if other change stream event fields like updateDescription are not large.如果其他变更流事件字段（如updateDescription）不大，则可以在变更流输出中同时请求前映像和后映像。
  • Request only post-images in the change stream output for documents up to 16 megabytes if other change stream event fields like updateDescription are not large.如果其他更改流事件字段（如updateDescription）不太大，则请求在更改流输出中为高达16兆字节的文档后映像。
  • Request only pre-images in the change stream output for documents up to 16 megabytes if:如果出现以下情况，则仅在更改流输出中请求高达16兆字节的文档的前映像：
    • document updates affect only a small fraction of the document structure or content, and文档更新只影响文档结构或内容的一小部分，并且
    • do not cause a replace change event. A replace event always includes the post-image.不要引起replace更改事件。replace事件始终包括后映像。
• To request a pre-image, you set fullDocumentBeforeChange to required or whenAvailable in db.collection.watch(). 若要请求前映像，请在db.collection.watch()中将fullDocumentBeforeChange设置为required或whenAvailable。To request a post-image, you set fullDocument using the same method.若要请求后映像，请使用相同的方法设置fullDocument。
• Pre-images are written to the config.system.preimages collection.前映像将写入config.system.preimages集合。
  • The config.system.preimages collection may become large. config.system.preimages集合可能会变大。To limit the collection size, you can set expireAfterSeconds time for the pre-images as shown earlier.要限制集合大小，您可以为前映像设置expireAfterSeconds时间，如前所示。
  • Pre-images are removed asynchronously by a background process.前映像通过后台进程异步移除。

Create a View创建视图

A view definition pipeline cannot include the $out or the $merge stage. 视图定义pipeline不能包含$out或$merge阶段。This restriction also applies to embedded pipelines, such as pipelines used in $lookup or $facet stages.此限制也适用于嵌入式管道，例如$lookup或$facet阶段中使用的管道。

To create a view using the create command, use the following syntax:要使用create命令创建视图，请使用以下语法：

db.runCommand( { create: <view>, viewOn: <source>, pipeline: <pipeline> } )

or if specifying a collation:或者如果指定排序规则：

db.runCommand( { create: <view>, viewOn: <source>, pipeline: <pipeline>, collation: <collation> } )

For example, create a survey collection with the following documents:例如，使用以下文档创建survey集合：

db.survey.insertMany(
   [
      { _id: 1, empNumber: "abc123", feedback: { management: 3, environment: 3 }, department: "A" },
      { _id: 2, empNumber: "xyz987", feedback: { management: 2, environment: 3 }, department: "B" },
      { _id: 3, empNumber: "ijk555", feedback: { management: 3, environment: 4 }, department: "A" }
   ]
)

The following operation creates a managementRatings view with the _id, feedback.management, and department fields:以下操作创建了一个managementRatings视图，其中包含_id、feedback.management和department字段：

db.runCommand ( {
   create: "managementFeedback",
   viewOn: "survey",
   pipeline: [ { $project: { "management": "$feedback.management", department: 1 } } ]
} )

Specify Collation指定排序规则

You can specify collation at the collection or view level. 可以在集合或视图级别指定排序规则。For example, the following operation creates a collection, specifying a collation for the collection (See Collation Document for descriptions of the collation fields):例如，以下操作创建集合，指定集合的排序规则（有关排序规则字段的描述，请参阅排序规则文档）：

db.runCommand ( {
   create: "myColl",
   collation: { locale: "fr" }
});

This collation will be used by indexes and operations that support collation unless they explicitly specify a different collation. For example, insert the following documents into myColl:支持排序规则的索引和操作将使用此排序规则，除非它们明确指定了不同的排序规则。例如，将以下文档插入myColl：

{ _id: 1, category: "café" }
{ _id: 2, category: "cafe" }
{ _id: 3, category: "cafE" }

The following operation uses the collection's collation:以下操作使用集合的排序规则：

db.myColl.find().sort( { category: 1 } )

The operation returns documents in the following order:该操作按以下顺序返回文档：

{ "_id" : 2, "category" : "cafe" }
{ "_id" : 3, "category" : "cafE" }
{ "_id" : 1, "category" : "café" }

The same operation on a collection that uses simple binary collation (i.e. no specific collation set) returns documents in the following order:对使用简单二进制排序规则（即没有特定的排序规则集）的集合执行的相同操作按以下顺序返回文档：

{ "_id" : 3, "category" : "cafE" }
{ "_id" : 2, "category" : "cafe" }
{ "_id" : 1, "category" : "café" }

Specify Storage Engine Options指定存储引擎选项

You can specify collection-specific storage engine configuration options when you create a collection with db.createCollection(). 使用db.createCollection()创建集合时，可以指定特定于集合的存储引擎配置选项。Consider the following operation:考虑以下操作：

db.runCommand( {
    create: "users",
    storageEngine: { wiredTiger: { configString: "<option>=<setting>" } }
} )

This operation creates a new collection named users with a specific configuration string that MongoDB will pass to the wiredTiger storage engine. 此操作将创建一个名为users的新集合，其中包含MongoDB将传递给wiredTiger存储引擎的特定配置字符串。See the WiredTiger documentation of collection level options for specific wiredTiger options.有关特定的WiredTiger选项，请参阅集合级别选项的WiredTinger文档。