$exists¶
Definition¶
$exists
¶Syntax:
{ field: { $exists: <boolean> } }
When
<boolean>
is true,$exists
matches the documents that contain the field, including documents where the field value isnull
. If<boolean>
is false, the query returns only the documents that do not contain the field. [1]MongoDB
$exists
does not correspond to SQL operatorexists
. For SQLexists
, refer to the$in
operator.
[1] | Starting in MongoDB 4.2, users can no longer use the query filter
$type: 0 as a synonym for
$exists:false . To query for null or missing fields, see
Query for Null or Missing Fields. |
Examples¶
Exists and Not Equal To¶
Consider the following example:
db.inventory.find( { qty: { $exists: true, $nin: [ 5, 15 ] } } )
This query will select all documents in the inventory
collection
where the qty
field exists and its value does not equal 5
or
15
.
Null Values¶
The following examples uses a collection named records
with the
following documents:
{ a: 5, b: 5, c: null } { a: 3, b: null, c: 8 } { a: null, b: 3, c: 9 } { a: 1, b: 2, c: 3 } { a: 2, c: 5 } { a: 3, b: 2 } { a: 4 } { b: 2, c: 4 } { b: 2 } { c: 6 }
$exists: true
¶
The following query specifies the query predicate a: { $exists: true }
:
db.records.find( { a: { $exists: true } } )
The results consist of those documents that contain the field a
,
including the document whose field a
contains a null value:
{ a: 5, b: 5, c: null } { a: 3, b: null, c: 8 } { a: null, b: 3, c: 9 } { a: 1, b: 2, c: 3 } { a: 2, c: 5 } { a: 3, b: 2 } { a: 4 }
$exists: false
¶
The following query specifies the query predicate b: { $exists: false }
:
db.records.find( { b: { $exists: false } } )
The results consist of those documents that do not contain the field
b
:
{ a: 2, c: 5 } { a: 4 } { c: 6 }
Starting in MongoDB 4.2, users can no longer use the query filter
$type: 0
as a synonym for
$exists:false
. To query for null or missing fields, see
Query for Null or Missing Fields.