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db.createView()¶

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Behavior
Access Control
Examples

db.createView()¶

Note

The following page discusses views. For discussion of on-demand materialized views, see $merge instead.

Creates a view as the result of the applying the specified aggregation pipeline to the source collection or view. Views act as read-only collections, and are computed on demand during read operations. You must create views in the same database as the source collection. MongoDB executes read operations on views as part of the underlying aggregation pipeline.

The view definition pipeline cannot include the $out or the $merge stage. If the view definition includes nested pipeline (e.g. the view definition includes $lookup or $facet stage), this restriction applies to the nested pipelines as well.

The db.createView has the following syntax:

db.createView(<view>, <source>, <pipeline>, <options>)

The method accepts the following parameters:

Parameter	Type	Description
`view`	string	The name of the view to create.
`source`	string	The name of the source collection or view from which to create the view. The name is not the full namespace of the collection or view; i.e. does not include the database name and implies the same database as the view to create. You must create views in the same database as the source collection.
`pipeline`	array	An array that consists of the aggregation pipeline stage(s). `db.createView` creates the view by applying the specified `pipeline` to the `source` collection or view. The view definition `pipeline` cannot include the `$out` or the `$merge` stage. If the view definition includes nested pipeline (e.g. the view definition includes `$lookup` or `$facet` stage), this restriction applies to the nested pipelines as well. 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.
`options`	document	Optional. Additional options for the method.

The options document contains the following option field:

Field Type Description

collation

document

Optional. Specifies the default collation for the view.

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

If the underlying source is a collection, the view does not inherit the collection’s collation settings.

If no collation is specified, the view’s default collation is the “simple” binary comparison collator.

If the underlying source is another view, the view must specify the same collation settings.

The collation option has the following syntax:

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

When specifying collation, the locale field is mandatory; all other collation fields are optional. For descriptions of the fields, see Collation Document.

New in version 3.4.

The db.createView() method wraps the following create command operation:

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

Operations that lists collections, such as db.getCollectionInfos() and db.getCollectionNames(), includes views in their outputs.

Important

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.

To remove a view, use the drop() method on the view.

Behavior¶

Views exhibit the following behavior:

Read Only¶

Views are read-only; write operations on views will error.

The following read operations can support views:

Index Use and Sort Operations¶

Views use the indexes of the underlying collection.
As the indexes are on the underlying collection, you cannot create, drop or re-build indexes on the view directly nor get a list of indexes on the view.
Starting in MongoDB 4.4, you can specify a $natural sort when running a find command on a view. Prior versions of MongoDB do not support $natural sort on views.
The view’s underlying aggregation pipeline is subject to the 100 megabyte memory limit for blocking sort and blocking group operations. Starting in MongoDB 4.4, you can issue a find command with allowDiskUse: true on the view to allow MongoDB to use temporary files for blocking sort and group operations.

Prior to MongoDB 4.4, only the aggregate command accepted the allowDiskUse option.

See also

For more information on blocking sort operation memory limits, see Sort Operations.

Projection Restrictions¶

find() operations on views do not support the following projection operators:

Immutable Name¶

You cannot rename views.

View Creation¶

Views are computed on demand during read operations, and MongoDB executes read operations on views as part of the underlying aggregation pipeline. As such, views do not support operations such as:
- db.collection.mapReduce(),
- $text operator, since $text operation in aggregation is valid only for the first stage,
- $geoNear pipeline stage.
If the aggregation pipeline used to create the view suppresses the _id field, documents in the view do not have the _id field.

Sharded View¶

Views are considered sharded if their underlying collection is sharded. As such, you cannot specify a sharded view for the from field in $lookup and $graphLookup operations.

Views and Collation¶

You can specify a default collation for a view at creation time. If no collation is specified, the view’s default collation is the “simple” binary comparison collator. That is, the view does not inherit the collection’s default collation.
String comparisons on the view use the view’s default collation. An operation that attempts to change or override a view’s default collation will fail with an error.
If creating a view from another view, you cannot specify a collation that differs from the source view’s collation.
If performing an aggregation that involves multiple views, such as with $lookup or $graphLookup, the views must have the same collation.

Resource Locking¶

Changed in version 4.2.

db.createView() 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.createView() releases the lock. db.createView() 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.createView() obtained an exclusive lock on the parent database, blocking all operations on the database and all its collections until the operation completed.

Access Control¶

If the deployment enforces authentication, db.createView() requires that the authenticated user have the createCollection privilege on the database.

However, if the user has the createCollection on the database and find on the view to create, the user must also have the following additional permissions:

find on the source collection or view.
find on any other collections or views referenced in the pipeline, if any.

A user with the readWrite built in role on the database has the required privileges to run the listed operations. Either create a user with the required role or grant the role to an existing user

Examples¶

Create a View from a Single Collection¶

Given a collection survey with the following documents:

{ _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 managementFeedback view with the _id, feedback.management, and department fields:

db.createView(
   "managementFeedback",
   "survey",
   [ { $project: { "management": "$feedback.management", department: 1 } } ]
)

Query a View¶

To query the view, you can use db.collection.find() on the view:

db.managementFeedback.find()

The operation returns the following documents:

{ "_id" : 1, "department" : "A", "management" : 3 }
{ "_id" : 2, "department" : "B", "management" : 2 }
{ "_id" : 3, "department" : "A", "management" : 3 }

Perform Aggregation Pipeline on a View¶

The following operation performs an aggregation on the managementFeedback view, using the $sortByCount to group by the department field and sort in descending order by the count of each distinct department:

db.managementFeedback.aggregate([ { $sortByCount: "$department" } ] )

The operation returns the following documents:

{ "_id" : "A", "count" : 2 }
{ "_id" : "B", "count" : 1 }

Create a View from Multiple Collections¶

Given the following two collections:

The orders collection:

{ "_id" : 1, "item" : "abc", "price" : NumberDecimal("12.00"), "quantity" : 2 }
{ "_id" : 2, "item" : "jkl", "price" : NumberDecimal("20.00"), "quantity" : 1 }
{ "_id" : 3, "item" : "abc", "price" : NumberDecimal("10.95"), "quantity" : 5 }
{ "_id" : 4, "item" : "xyz", "price" : NumberDecimal("5.95"), "quantity" : 5 }
{ "_id" : 5, "item" : "xyz", "price" : NumberDecimal("5.95"), "quantity" : 10 }

The inventory collection:

{ "_id" : 1, "sku" : "abc", description: "product 1", "instock" : 120 }
{ "_id" : 2, "sku" : "def", description: "product 2", "instock" : 80 }
{ "_id" : 3, "sku" : "ijk", description: "product 3", "instock" : 60 }
{ "_id" : 4, "sku" : "jkl", description: "product 4", "instock" : 70 }
{ "_id" : 5, "sku" : "xyz", description: "product 5", "instock" : 200 }

The following db.createView() example specifies a $lookup stage to create a view from the join of the two collections:

db.createView (
   "orderDetails",
   "orders",
   [
     { $lookup: { from: "inventory", localField: "item", foreignField: "sku", as: "inventory_docs" } },
     { $project: { "inventory_docs._id": 0, "inventory_docs.sku": 0 } }
   ]
)

Query a View¶

To query the view, you can use db.collection.find() on the view:

db.orderDetails.find()

The operation returns the following documents:

{
   "_id" : 1,
   "item" : "abc",
   "price" : NumberDecimal("12.00"),
   "quantity" : 2,
   "inventory_docs" : [ { "description" : "product 1", "instock" : 120 } ]
}
{
   "_id" : 2,
   "item" : "jkl",
   "price" : NumberDecimal("20.00"),
   "quantity" : 1,
   "inventory_docs" : [ { "description" : "product 4", "instock" : 70 } ]
}
{
   "_id" : 3,
   "item" : "abc",
   "price" : NumberDecimal("10.95"),
   "quantity" : 5,
   "inventory_docs" : [ { "description" : "product 1", "instock" : 120 } ]
}
{
   "_id" : 4,
   "item" : "xyz",
   "price" : NumberDecimal("5.95"),
   "quantity" : 5,
   "inventory_docs" : [ { "description" : "product 5", "instock" : 200 } ]
}
{
   "_id" : 5,
   "item" : "xyz",
   "price" : NumberDecimal("5.95"),
   "quantity" : 10,
   "inventory_docs" : [ { "description" : "product 5", "instock" : 200 } ]
}

Perform Aggregation Pipeline on a View¶

The following operation performs an aggregation on the orderDetails view, using the $sortByCount to group by the item field and sort in descending order by the count of each distinct item:

db.orderDetails.aggregate( [ { $sortByCount: "$item" } ] )

The operation returns the following documents:

{ "_id" : "xyz", "count" : 2 }
{ "_id" : "abc", "count" : 2 }
{ "_id" : "jkl", "count" : 1 }

Create a View with Default Collation¶

Given the places collection with the following document:

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

The following operation creates a view, specifying collation at the view level:

db.createView(
   "placesView",
   "places",
   [ { $project: { category: 1 } } ],
   { collation: { locale: "fr", strength: 1 } }
)

String comparisons on the view use the view’s default collation. For example, the following operation uses the view’s collation:

db.placesView.count( { category: "cafe" } )

The operation returns 3.

An operation that attempts to change or override a view’s default collation will fail with an error.

See also

Collation and Views

← db.createCollection() db.currentOp() →