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collMod

Definition

collMod

collMod makes it possible to add options to a collection or to modify view definitions. The command takes the following prototype form:

db.runCommand( {"collMod" : <collection or view> , "<option>" : <value> } )

In this command, substitute <collection or view> with the name of a collection or view in the current database, and <option> and <value> with the option and value you want to set.

Use the userFlags field in the db.collection.stats() output to check the options enabled for a collection.

Options

TTL Collections

index

The index option changes the expiration time of a TTL Collection.

Specify the key or index name, and new expiration time with a document of the form:

{keyPattern: <index_spec> || name: <index_name>, expireAfterSeconds: <seconds> }

In this example, <index_spec> is an existing index in the collection. In cases of multiple indexes with the same key pattern, the user is required to specify the index by name. seconds is the number of seconds to subtract from the current time.

On success collMod returns a document with fields expireAfterSeconds_old and expireAfterSeconds_new set to their respective values.

On failure, collMod returns a document with no expireAfterSeconds field to update if there is no existing expireAfterSeconds field or cannot find index { **key**: 1.0 } for ns **namespace** if the specified keyPattern does not exist.

Record Allocation

noPadding

New in version 3.0.

noPadding is available for the MMAPv1 storage engine only.

noPadding disables record padding for the collection. Without padding, the record allocation size corresponds to the document size, and any updates that results in document growth will require a new allocation.

Warning

Only set noPadding to true for collections whose workloads have no update operations that cause documents to grow, such as for collections with workloads that are insert-only. For more information, see No Padding Allocation Strategy.

usePowerOf2Sizes

Deprecated since version 3.0.

usePowerOf2Sizes is available for the MMAPv1 storage engine only.

usePowerOf2Sizes has no effect on the allocation strategy. MongoDB 3.0 uses the power of 2 allocation as the default record allocation strategy for MMAPv1.

To disable the power of 2 allocation for a collection, use the collMod command with the noPadding option or the db.createCollection() method with the noPadding option. For more information, see MMAPv1 Record Allocation Behavior Changes.

Document Validation

validator

New in version 3.2.

validator allows users to specify validation rules or expressions for a collection. For more information, see Schema Validation.

The validator option takes a document that specifies the validation rules or expressions. You can specify the expressions using the same operators as the query operators with the exception of : $geoNear, $near, $nearSphere, $text, and $where.

Note

  • Validation occurs during updates and inserts. Existing documents do not undergo validation checks until modification.
  • You cannot specify a validator for collections in the admin, local, and config databases.
  • You cannot specify a validator for system.* collections.
validationLevel

New in version 3.2.

The validationLevel determines how strictly MongoDB applies the validation rules to existing documents during an update.

validationLevel Description
"off" No validation for inserts or updates.
"strict" Default Apply validation rules to all inserts and all updates.
"moderate" Apply validation rules to inserts and to updates on existing valid documents. Do not apply rules to updates on existing invalid documents.
validationAction

New in version 3.2.

The validationAction option determines whether to error on invalid documents or just warn about the violations but allow invalid documents.

Important

Validation of documents only applies to those documents as determined by the validationLevel.

validationAction Description
"error" Default Documents must pass validation before the write occurs. Otherwise, the write operation fails.
"warn" Documents do not have to pass validation. If the document fails validation, the write operation logs the validation failure.

To view the validation specifications for a collection, use the db.getCollectionInfos() method.

Views

viewOn

The underlying source collection or view for the view. The view definition is determined by applying the specified pipeline to this source.

Required if modifying a view on a MongoDB deployment that is running with access control.

pipeline

The aggregation pipeline that defines the view.

Required if modifying a view on a MongoDB deployment that is running with access control.

The view definition is public; i.e. db.getCollectionInfos() and explain operations on the view will include the pipeline that defines the view. As such, avoid referring directly to sensitive fields and values in view definitions.

Access Control

If the deployment enforces authentication/authorization, you must have the following privilege to run the collMod command:

  Required Privileges
Modify a non-capped collection collMod in the database
Modify a view

collMod in the database and either:

  • no find on the view to modify, or
  • both find on the view to modify and find on the source collection/view.

The built-in role dbAdmin provides the required privileges.

Examples

Change Expiration Value for Indexes

To update the expiration value for a collection named sessions indexed on a lastAccess field from 30 minutes to 60 minutes, use the following operation:

db.runCommand( { collMod: "sessions",
                 index: { keyPattern: { lastAccess: 1 },
                          expireAfterSeconds: 3600
                        }
})

Which will return the document:

{ "expireAfterSeconds_old" : 1800, "expireAfterSeconds_new" : 3600, "ok" : 1 }

Add Document Validation to an Existing Collection

The following example adds a validator to an existing collection named contacts.

Note

MongoDB 3.6 adds the $jsonSchema operator to support JSON Schema validation.

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"
         }
      }
   } },
   validationLevel: "moderate",
   validationAction: "warn"
} )

With the moderate validationLevel, MongoDB applies validation rules to insert operations and to update operationss to existing documents that already fulfill the validation criteria. Updates to existing documents that do not fulfill the validation criteria are not checked for validity.

With the warn validationAction, MongoDB logs any violations but allows the insertion or update to proceed.

For example, the following insert operation violates the validation rule.

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

However, since the validationAction is warn only, MongoDB only logs the validation violation message and allows the operation to proceed:

2017-12-01T12:31:23.738-0500 W STORAGE  [conn1] Document would fail validation collection: example.contacts doc: { _id: ObjectId('5a2191ebacbbfc2bdc4dcffc'), name: "Amanda", status: "Updated" }

For more information, see Schema Validation.