Find document that matches same array elements in MongoDB?

To find a document that matches the same array elements in MongoDB, use the $all operator combined with $size. The $all operator selects documents where the array field contains all specified elements, while $size ensures the array has exactly the required number of elements.

Syntax

db.collection.find({
    "arrayField": { 
        $all: ["element1", "element2", "element3"], 
        $size: numberOfElements 
    }
});

Sample Data

db.demo543.insertMany([
    {id: 101, subject: ["MySQL", "Java", "C", "Python"]},
    {id: 102, subject: ["MySQL", "MongoDB", "SQL Server"]}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e8e1b2f9e5f92834d7f05c9"),
        ObjectId("5e8e1b2f9e5f92834d7f05ca")
    ]
}

Display all documents in the collection ?

db.demo543.find();

{ "_id": ObjectId("5e8e1b2f9e5f92834d7f05c9"), "id": 101, "subject": ["MySQL", "Java", "C", "Python"] }
{ "_id": ObjectId("5e8e1b2f9e5f92834d7f05ca"), "id": 102, "subject": ["MySQL", "MongoDB", "SQL Server"] }

Example

Find the document that contains exactly the same array elements: MySQL, MongoDB, and SQL Server ?

db.demo543.find({
    "subject": { 
        $all: ["MySQL", "MongoDB", "SQL Server"], 
        $size: 3 
    }
});

{ "_id": ObjectId("5e8e1b2f9e5f92834d7f05ca"), "id": 102, "subject": ["MySQL", "MongoDB", "SQL Server"] }

Key Points

• $all ensures all specified elements are present in the array
• $size ensures the array has exactly the specified number of elements
• Without $size, arrays with additional elements would also match

Conclusion

Use $all with $size to find documents with arrays containing exactly the same elements. This combination prevents matching arrays with additional unwanted elements.