Find Strings greater than a particular length in MongoDB?

To find strings with a length greater than a particular value in MongoDB, use the $where operator with JavaScript expressions to access the string's length property.

Syntax

db.collectionName.find({
    $where: 'this.fieldName.length > value'
});

Sample Data

Let us create a collection with user documents to demonstrate string length filtering ?

db.stringFieldLengthDemo.insertMany([
    {"UserId": 1, "UserName": "Adam Smith"},
    {"UserId": 2, "UserName": "Carol Taylor"}, 
    {"UserId": 3, "UserName": "James Brown"},
    {"UserId": 4, "UserName": "John Smith"},
    {"UserId": 5, "UserName": "David Miller"},
    {"UserId": 6, "UserName": "John Williams"},
    {"UserId": 7, "UserName": "Chris Evans"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c77bb4b2386c62d05142a78"),
        ObjectId("5c77bb562386c62d05142a79"),
        ObjectId("5c77bb5b2386c62d05142a7a"),
        ObjectId("5c77bb662386c62d05142a7b"),
        ObjectId("5c77bb892386c62d05142a7c"),
        ObjectId("5c77bbb02386c62d05142a7d"),
        ObjectId("5c77bbd32386c62d05142a7e")
    ]
}

Display All Documents

db.stringFieldLengthDemo.find();

{
    "_id": ObjectId("5c77bb4b2386c62d05142a78"),
    "UserId": 1,
    "UserName": "Adam Smith"
}
{
    "_id": ObjectId("5c77bb562386c62d05142a79"),
    "UserId": 2,
    "UserName": "Carol Taylor"
}
{
    "_id": ObjectId("5c77bb5b2386c62d05142a7a"),
    "UserId": 3,
    "UserName": "James Brown"
}
{
    "_id": ObjectId("5c77bb662386c62d05142a7b"),
    "UserId": 4,
    "UserName": "John Smith"
}
{
    "_id": ObjectId("5c77bb892386c62d05142a7c"),
    "UserId": 5,
    "UserName": "David Miller"
}
{
    "_id": ObjectId("5c77bbb02386c62d05142a7d"),
    "UserId": 6,
    "UserName": "John Williams"
}
{
    "_id": ObjectId("5c77bbd32386c62d05142a7e"),
    "UserId": 7,
    "UserName": "Chris Evans"
}

Example: Find Strings Longer Than 11 Characters

Query to find usernames with more than 11 characters ?

db.stringFieldLengthDemo.find({
    $where: 'this.UserName.length > 11'
});

{
    "_id": ObjectId("5c77bb562386c62d05142a79"),
    "UserId": 2,
    "UserName": "Carol Taylor"
}
{
    "_id": ObjectId("5c77bb892386c62d05142a7c"),
    "UserId": 5,
    "UserName": "David Miller"
}
{
    "_id": ObjectId("5c77bbb02386c62d05142a7d"),
    "UserId": 6,
    "UserName": "John Williams"
}

Key Points

• The $where operator executes JavaScript expressions on each document
• Use this.fieldName.length to access the string length property
• This method is slower than indexed queries, so use sparingly on large collections

Conclusion

The $where operator with JavaScript expressions provides a flexible way to filter documents based on string length. While powerful, consider performance implications for large datasets.