db.createCollection()

Resource Locking

db.createCollection() obtains an exclusive lock on the specified collection or view for the duration of the operation. All subsequent operations on the collection must wait until db.createCollection() releases the lock. db.createCollection() typically holds this lock for a short time.

Creating a view requires obtaining an additional exclusive lock on the system.views collection in the database. This lock blocks creation or modification of views in the database until the command completes.

Prior to MongoDB 4.2, db.createCollection() obtained an exclusive lock on the parent database, blocking all operations on the database and all its collections until the operation completed.

Transactions

You can create collections and indexes inside a distributed transaction if the transaction is not a cross-shard write transaction.

To use db.createCollection() in a transaction, the transaction must use read concern "local". If you specify a read concern level other than "local", the transaction fails.

Create 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.

See Capped Collections for more information about capped collections.

Create a Collection with Document Validation

Collections with validation compare each inserted or updated document against the criteria specified in the validator option. Depending on the validationLevel and validationAction, MongoDB either returns a warning, or refuses to insert or update the document if it fails to meet the specified criteria.

The following example creates a contacts collection with a JSON Schema validator:

db.createCollection( "contacts", {
   validator: { $jsonSchema: {
      bsonType: "object",
      required: [ "phone" ],
      properties: {
         phone: {
            bsonType: "string",
            description: "must be a string and is required"
         },
         email: {
            bsonType : "string",
            pattern : "@mongodb\.com$",
            description: "must be a string and match the regular expression pattern"
         },
         status: {
            enum: [ "Unknown", "Incomplete" ],
            description: "can only be one of the enum values"
         }
      }
   } }
} )

With the validator in place, the following insert operation fails validation:

db.contacts.insert( { name: "Amanda", status: "Updated" } )

The method returns the error in the WriteResult:

WriteResult({
   "nInserted" : 0,
   "writeError" : {
      "code" : 121,
      "errmsg" : "Document failed validation"
   }
})

For more information, see Schema Validation. To view the validation specifications for a collection, use the db.getCollectionInfos() method.

Specify Collation

Collation allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.

You can specify collation at the collection or view level. For example, the following operation creates a collection, specifying a collation for the collection (See Collation Document for descriptions of the collation fields):

db.createCollection( "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:

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

The following operation uses the collection's collation:

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

The operation returns documents in the following order:

{ "_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:

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

Specify Storage Engine Options

You can specify collection-specific storage engine configuration options when you create a collection with db.createCollection(). Consider the following operation:

db.createCollection(
   "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.

For example, to specify the zlib compressor for file blocks in the users collection, set the block_compressor option with the following command:

db.createCollection(
   "users",
   { storageEngine: { wiredTiger: { configString: "block_compressor=zlib" } } }
)