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$elemMatch (query predicate operator)

Tip

$elemMatch (projection operator)

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>, ... } } }

Behavior

You cannot specify a $where operator in an $elemMatch.
You cannot specify a $text query operator 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 because 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 } ] },
   { "_id": 5, "results": { "product": "xyz", "score": 7 } }
] )

The document with an _id of 5 doesn't contain an array. The document is included to show that $elemMatch matches only array elements.

The following query matches documents where results contains at least one element where product is "xyz" and score is 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

The following sections show the output differences when you use $elemMatch with a single query condition, and omit $elemMatch.

Example 1

Query with $elemMatch:

db.survey.find(
   { results: { $elemMatch: { product: "xyz" } } }
)

The query returns documents where any product in results is "xyz":

[
   {
      _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 } ]
   }
]

Query without $elemMatch:

db.survey.find(
   { "results.product": "xyz" }
)

In the following output, notice that the document with an _id of 5 (which doesn't contain an array) is also included:

[
   {
      _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: 5, results: { product: 'xyz', score: 7 } }
]

Example 2

Consider the following queries:

First query has a single <query> condition in $elemMatch.
Second query omits $elemMatch.

First query with $elemMatch:

db.survey.find(
   { "results": { $elemMatch: { product: { $ne: "xyz" } } } }
)

The query returns documents that has a product with value other than "xyz":

{ "_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 } ] }

Second query without $elemMatch:

db.survey.find(
   { "results.product": { $ne: "xyz" } }
)

The query returns documents where none of the product results are "xyz":

{ "_id" : 4, "results" : [ { "product" : "abc", "score" : 7 },
                           { "product" : "def", "score" : 8 } ] }

Both queries include the document with an _id of 4, and omit the document with an _id of 5 because the product is "xyz".

Learn More

For additional examples on querying arrays, see:

For additional examples on querying, see Query Documents.

Tip

db.collection.find()

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