$elemMatch (query)
Definition
$elemMatch
The
$elemMatch
operator matches documents that contain an array field with at least one element that matches all the specified query criteria.
Compatibility
You can use $elemMatch
for deployments hosted in the following
environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
Syntax
{ <field>: { $elemMatch: { <query1>, <query2>, ... } } }
If you specify only a single <query>
condition in the
$elemMatch
expression, and are not using the $not
or $ne
operators inside of $elemMatch
,
$elemMatch
can be omitted. See
Single Query Condition.
Behavior
You cannot specify a
$where
expression in an$elemMatch
.You cannot specify a
$text
query expression in an$elemMatch
.
Examples
Element Match
Given the following documents in the scores
collection:
{ _id: 1, results: [ 82, 85, 88 ] } { _id: 2, results: [ 75, 88, 89 ] }
The following query matches only those documents where the results
array contains at least one element that is both greater than or equal
to 80
and is less than 85
:
db.scores.find( { results: { $elemMatch: { $gte: 80, $lt: 85 } } } )
The query returns the following document since the element 82
is
both greater than or equal to 80
and is less than 85
:
{ "_id" : 1, "results" : [ 82, 85, 88 ] }
For more information on specifying multiple criteria on array elements, see Specify Multiple Conditions for Array Elements.
Array of Embedded Documents
This statement inserts documents into the survey
collection:
db.survey.insertMany( [ { "_id": 1, "results": [ { "product": "abc", "score": 10 }, { "product": "xyz", "score": 5 } ] }, { "_id": 2, "results": [ { "product": "abc", "score": 8 }, { "product": "xyz", "score": 7 } ] }, { "_id": 3, "results": [ { "product": "abc", "score": 7 }, { "product": "xyz", "score": 8 } ] }, { "_id": 4, "results": [ { "product": "abc", "score": 7 }, { "product": "def", "score": 8 } ] } ] )
The following query matches only those documents where the results
array contains at least one element with both product
equal to
"xyz"
and score
greater than or equal to 8
:
db.survey.find( { results: { $elemMatch: { product: "xyz", score: { $gte: 8 } } } } )
Specifically, the query matches the following document:
{ "_id" : 3, "results" : [ { "product" : "abc", "score" : 7 }, { "product" : "xyz", "score" : 8 } ] }
Single Query Condition
If you specify a single query predicate in the $elemMatch
expression, and are not using the $not
or $ne
operators inside of $elemMatch
, $elemMatch
can be
omitted.
The following examples return the same documents.
With $elemMatch
:
db.survey.find( { results: { $elemMatch: { product: "xyz" } } } )
Without $elemMatch
:
db.survey.find( { "results.product": "xyz" } )
However, if your $elemMatch
expression contains the
$not
or $ne
operators then omitting the
$elemMatch
expression changes the documents returned.
The following examples return different documents.
With $elemMatch
:
db.survey.find( { "results": { $elemMatch: { product: { $ne: "xyz" } } } } )
Without $elemMatch
:
db.survey.find( { "results.product": { $ne: "xyz" } } )
With $elemMatch
, the first query returns these documents:
{ "_id" : 1, "results" : [ { "product" : "abc", "score" : 10 }, { "product" : "xyz", "score" : 5 } ] } { "_id" : 2, "results" : [ { "product" : "abc", "score" : 8 }, { "product" : "xyz", "score" : 7 } ] } { "_id" : 3, "results" : [ { "product" : "abc", "score" : 7 }, { "product" : "xyz", "score" : 8 } ] } { "_id" : 4, "results" : [ { "product" : "abc", "score" : 7 }, { "product" : "def", "score" : 8 } ] }
Without $elemMatch
, the second query returns this
document:
{ "_id" : 4, "results" : [ { "product" : "abc", "score" : 7 }, { "product" : "def", "score" : 8 } ] }
The first query returns the documents where any product in the
results
array is not "xyz"
. The second query returns the
documents where all of the products in the results
array are not
"xyz"
.
Additional Examples
For additional examples in querying arrays, see:
For additional examples in querying, see: