MongoDB query to match documents that contain an array field

To match documents that contain an array field, use the $elemMatch operator. This operator matches documents where at least one array element meets all specified criteria within a single element.

Syntax

db.collection.find({
    "arrayField": {
        "$elemMatch": {
            "field1": "value1",
            "field2": "value2"
        }
    }
});

Sample Data

Let us create a collection with documents ?

db.demo592.insertMany([
    {
        "id": 101,
        "details": [
            { "Name": "Chris", "Value": "200" },
            { "Name": "David", "Value": "800" }
        ]
    },
    {
        "id": 102,
        "details": [
            { "Name": "Chris", "Value": "500" },
            { "Name": "David", "Value": "900" }
        ]
    }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e930d8ffd2d90c177b5bcd6"),
        ObjectId("5e930d90fd2d90c177b5bcd7")
    ]
}

Display All Documents

db.demo592.find();

{ "_id": ObjectId("5e930d8ffd2d90c177b5bcd6"), "id": 101, "details": [
    { "Name": "Chris", "Value": "200" },
    { "Name": "David", "Value": "800" }
] }
{ "_id": ObjectId("5e930d90fd2d90c177b5bcd7"), "id": 102, "details": [
    { "Name": "Chris", "Value": "500" },
    { "Name": "David", "Value": "900" }
] }

Example: Complex Array Matching

Find documents where both Chris has Value >= 500 AND David has Value >= 600 ?

db.demo592.find({
    "$and": [
        { "details": { "$elemMatch": { "Name": "Chris", "Value": { "$gte": "500" } } } },
        { "details": { "$elemMatch": { "Name": "David", "Value": { "$gte": "600" } } } }
    ]
});

{ "_id": ObjectId("5e930d90fd2d90c177b5bcd7"), "id": 102, "details": [
    { "Name": "Chris", "Value": "500" },
    { "Name": "David", "Value": "900" }
] }

Key Points

• $elemMatch ensures all conditions are met within a single array element
• Use $and to match multiple array elements with different criteria
• Without $elemMatch, conditions might match across different array elements

Conclusion

The $elemMatch operator is essential for querying arrays in MongoDB. It ensures that all specified conditions are satisfied by the same array element, providing precise matching for complex array queries.