db.createCollection()¶

Definition¶

db.createCollection(name, options)¶

Creates a new collection explicitly.

Because MongoDB creates a collection implicitly when the collection is first referenced in a command, this method is used primarily for creating new capped collections. This is also used to pre-allocate space for an ordinary collection.

The db.createCollection() method has the following prototype form:

db.createCollection(name, {capped: <boolean>, autoIndexId: <boolean>, size: <number>, max: <number>} )

The db.createCollection() method has the following parameters:

Parameter	Type	Description
`name`	string	The name of the collection to create.
`options`	document	Optional. Configuration options for creating a capped collection or for preallocating space in a new collection.

The options document creates a capped collection or preallocates space in a new ordinary collection. The options document contains the following fields:

Field	Type	Description
`capped`	Boolean	Optional. Enables a capped collection. To create a capped collection, specify `true`. If you specify `true`, you must also set a maximum size in the `size` field.
`autoIndexId`	Boolean	Optional. Specify `false` to disable the automatic creation of an index on the `_id` field. Before 2.2, the default value for `autoIndexId` was `false`. See _id Fields and Indexes on Capped Collections for more information. Do not set `autoIndexId` to `true` for replicated collections.
`size`	number	Optional. Specifies a maximum size in bytes for a capped collection. The `size` field is required for capped collections, and ignored for other collections.
`max`	number	Optional. The maximum number of documents allowed in the capped collection. The `size` limit takes precedence over this limit. If a capped collection reaches its maximum `size` before it reaches the maximum number of documents, MongoDB removes old documents. If you prefer to use this limit, ensure that the `size` limit, which is required, is sufficient to contain the documents limit.
`usePowerOf2Sizes`	boolean	Optional. 2.6 新版功能: `usePowerOf2Sizes` became an option to `db.createCollection()` when `usePowerOf2Sizes` became the default allocation strategy for all new collections by default. Set to `false` to disable the `usePowerOf2Sizes` allocation strategy for this collection. Defaults to `true` unless the `newCollectionsUsePowerOf2Sizes` parameter is set to `false`.

Example¶

The following example creates a capped collection. Capped collections have maximum size or document counts that prevent them from growing beyond maximum thresholds. All capped collections must specify a maximum size and may also specify a maximum document count. MongoDB removes older documents if a collection reaches the maximum size limit before it reaches the maximum document count. Consider the following example:

db.createCollection("log", { capped : true, size : 5242880, max : 5000 } )

This command creates a collection named log with a maximum size of 5 megabytes and a maximum of 5000 documents.

The following command simply pre-allocates a 2-gigabyte, uncapped collection named people:

db.createCollection("people", { size: 2147483648 } )

This command provides a wrapper around the database command create. See 限制集 for more information about capped collections.

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