Project Fields to Return from Query
On this page
- Return All Fields in Matching Documents
- Return the Specified Fields and the
_id
Field Only - Suppress
_id
Field - Return All But the Excluded Fields
- Return Specific Fields in Embedded Documents
- Suppress Specific Fields in Embedded Documents
- Projection on Embedded Documents in an Array
- Project Specific Array Elements in the Returned Array
- Project Fields with Aggregation Expressions
- Project Fields to Return from a Query with MongoDB Atlas
- Additional Considerations
You can query embedded documents in MongoDB by using the following methods:
Your programming language's driver.
The MongoDB Atlas UI. To learn more, see Project Fields to Return from a Query with MongoDB Atlas.
➤ Use the Select your language drop-down menu in the upper-right to set the language of the following examples or select MongoDB Compass.
By default, queries in MongoDB return all fields in matching documents. To limit the amount of data that MongoDB sends to applications, you can include a projection document to specify or restrict fields to return.
Return All Fields in Matching Documents
The following example returns all fields from all documents in the
inventory
collection where the status
equals "A"
:
The operation corresponds to the following SQL statement:
SELECT * from inventory WHERE status = "A"
Return the Specified Fields and the _id
Field Only
A projection can explicitly include several fields by setting the
<field>
to 1
in the projection document. The following
operation returns all documents that match the query. In the result
set, only the item
, status
and, by default, the _id
fields
return in the matching documents.
The operation corresponds to the following SQL statement:
SELECT _id, item, status from inventory WHERE status = "A"
Suppress _id
Field
You can remove the _id
field from the results by setting it to
0
in the projection, as in the following example:
The operation corresponds to the following SQL statement:
SELECT item, status from inventory WHERE status = "A"
Note
With the exception of the _id
field, you cannot combine inclusion
and exclusion statements in projection documents.
Return All But the Excluded Fields
Instead of listing the fields to return in the matching document, you
can use a projection to exclude specific fields. The following example
which returns all fields except for the status
and the instock
fields in the matching documents:
Note
With the exception of the _id
field, you cannot combine inclusion
and exclusion statements in projection documents.
Return Specific Fields in Embedded Documents
You can return specific fields in an embedded document. Use the
dot notation to refer to the embedded
field and set to 1
in the projection document.
The following example returns:
The
_id
field (returned by default),The
item
field,The
status
field,The
uom
field in thesize
document.
The uom
field remains embedded in the size
document.
You can also specify embedded fields using the nested form. For example,
{ item: 1, status: 1, size: { uom: 1 } }
.
Suppress Specific Fields in Embedded Documents
You can suppress specific fields in an embedded document. Use the
dot notation to refer to the embedded
field in the projection document and set to 0
.
The following example specifies a projection to exclude the uom
field inside the size
document. All other fields are returned in
the matching documents:
You can also specify embedded fields using the nested form. For example,
{ size: { uom: 0 } }
.
Projection on Embedded Documents in an Array
Use dot notation to project specific fields inside documents embedded in an array.
The following example specifies a projection to return:
The
_id
field (returned by default),The
item
field,The
status
field,The
qty
field in the documents embedded in theinstock
array.
Project Specific Array Elements in the Returned Array
Project Fields with Aggregation Expressions
You can specify aggregation expressions in a query projection. Aggregation expressions let you project new fields and modify the values of existing fields.
For example, the following operation uses aggregation expressions to
override the value of the status
field, and project new fields
area
and reportNumber
.
Note
The following example uses MongoDB Shell syntax. For driver examples of projection with aggregation, see your driver documentation.
db.inventory.find( { }, { _id: 0, item: 1, status: { $switch: { branches: [ { case: { $eq: [ "$status", "A" ] }, then: "Available" }, { case: { $eq: [ "$status", "D" ] }, then: "Discontinued" }, ], default: "No status found" } }, area: { $concat: [ { $toString: { $multiply: [ "$size.h", "$size.w" ] } }, " ", "$size.uom" ] }, reportNumber: { $literal: 1 } } )
[ { item: 'journal', status: 'Available', area: '294 cm', reportNumber: 1 }, { item: 'planner', status: 'Discontinued', area: '685.5 cm', reportNumber: 1 }, { item: 'notebook', status: 'Available', area: '93.5 in', reportNumber: 1 }, { item: 'paper', status: 'Discontinued', area: '93.5 in', reportNumber: 1 }, { item: 'postcard', status: 'Available', area: '152.5 cm', reportNumber: 1 } ]
Project Fields to Return from a Query with MongoDB Atlas
The example in this section uses the sample movies dataset. To learn how to load the sample dataset into your MongoDB Atlas deployment, see Load Sample Data.
To project fields to return from a query in MongoDB Atlas, follow these steps:
Specify the Filter field
Click More Options on the right side of the Filter field.
Specify the query filter.
Specify the query filter document in the Filter field. A query filter document uses query operators to specify search conditions.
Copy the following query filter document into the Filter search bar:
{ year: 1924 }
Click Apply
This query filter returns the following fields for all documents
in the sample_mflix.movies
collection where the year
field matches 1924
:
_id
title
plot
MongoDB Atlas returns the _id
field by default. To omit the
_id
field, copy the following project document
into the Project bar and click Apply:
{ title: 1, plot: 1, _id: 0 }
Additional Considerations
MongoDB enforces additional restrictions with regards to projections. See Projection Restrictions for details.