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Array Query Operators

$elemMatch (query)

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  • Definition
  • Compatibility
  • Syntax
  • Behavior
  • Examples
  • Learn More

Tip

See also:

$elemMatch (projection)

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

Syntax

{ <field>: { $elemMatch: { <query1>, <query2>, ... } } }

Behavior

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. That document is included to show that $elemMatch only matches array elements, which you will see in the following examples.

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 in querying arrays, see:

For additional examples in querying, see:

Tip

See also:

db.collection.find()

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