Views
A MongoDB view is a queryable object whose contents are defined by an aggregation pipeline on other collections or views. MongoDB does not persist the view contents to disk. A view's content is computed on-demand when a client queries the view. MongoDB can require clients to have permission to query the view. MongoDB does not support write operations against views.
For example, you can:
Create a view on a collection of employee data to
exclude
any private or personal information (PII). Applications can query the view for employee data that does not contain any PII.Create a view on a collection of collected sensor data to
add
computed fields and metrics. Applications can use simple find operations to query the data.Create a view that
joins
two collections containing inventory and order history respectively. Applications can query the joined data without managing or understanding the underlying complex pipeline.
You can create materialized views in the UI for deployments hosted in MongoDB Atlas.
When clients query a view, MongoDB appends the client query to the underlying pipeline and returns the results of that combined pipeline to the client. MongoDB may apply aggregation pipeline optimizations to the combined pipeline.
Note
The following page discusses views. For discussion of on-demand materialized views, see On-Demand Materialized Views instead.
Create View
To create or define a view:
Use the
db.createCollection()
method or thecreate
command:db.createCollection( "<viewName>", { "viewOn" : "<source>", "pipeline" : [<pipeline>], "collation" : { <collation> } } ) Use the
db.createView()
method:db.createView( "<viewName>", "<source>", [<pipeline>], { "collation" : { <collation> } } )
Note
- You must create views in the same database as the source collection.
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
$natural
sort when running afind
command on a view. Prior versions of MongoDB do not support$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 withallowDiskUse: 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 theallowDiskUse
option.
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:
If the aggregation pipeline used to create the view suppresses the
_id
field, documents in the view do not have the_id
field.
When you query a view, the:
Query
filter
,projection
,sort
,skip
,limit
, and other operations fordb.collection.find()
are converted to the equivalent aggregation pipeline stages.Converted aggregation pipeline stages are added to the end of the aggregation pipeline for the view. This does not modify the view's underlying pipeline, which is set when you create the view.
Aggregation pipeline optimizer reshapes the view aggregation pipeline stages to improve performance. This does not change the query results.
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.
Public View Definition
Operations that lists collections, such as
db.getCollectionInfos()
and
db.getCollectionNames()
, include 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.
Drop a View
To remove a view, use the db.collection.drop()
method on the
view.
Modify a View
You can modify a view either by dropping and recreating the view or
using the collMod
command.
Supported Operations
The following operations provide support for views, except for the restrictions mentioned in this page:
Commands | Methods |
---|---|