How Can Check Data Type Field in MongoDB?


Scott Campbell

How to Check Data Type Field in MongoDB

When working with MongoDB, it is essential to be able to check the data type of a field. This knowledge allows you to handle and manipulate the data effectively. In this tutorial, we will explore various ways to check the data type field in MongoDB.

Using the $type Operator

The $type operator in MongoDB allows you to check the data type of a field by specifying a numeric code representing each data type. Here is an example:

db.collection.find({ field: { $type: 2 } })

In the above example, we are checking if the ‘field’ has a data type of string. The number 2 corresponds to string data type as per MongoDB’s numeric codes for different types.

MongoDB Numeric Codes for Data Types:

  • 1: Double (64-bit floating-point number)
  • 2: String
  • 3: Object
  • 4: Array
  • 5: Binary Data
  • 6: Undefined (deprecated)
  • 7: ObjectId
  • 8: Boolean
  • 9: Date
  • -1:Timestamp

Determining Data Type using JavaScript typeof operator and db.eval()

If you prefer using JavaScript for data type checking, you can use the typeof operator in combination with db.eval().

db.eval(function() {
    var doc = db.findOne();
    return typeof doc.field;

In the above example, we are using db.eval() to execute a JavaScript function on the server-side. Inside the function, we retrieve a document from the collection and use typeof to determine the data type of the specific field.


The use of db.eval() should be avoided whenever possible as it can have security implications and impact performance.

Data Type Checking in Aggregation Pipeline

If you need to check data types during aggregation operations, MongoDB provides several operators like $type, $isNumber, and $isArray. These operators help you analyze and manipulate data based on their types within an aggregation pipeline.aggregate([
$match: {
field: { $type: “string” }

In this example, we are using the $match stage in an aggregation pipeline to filter out documents where the ‘field’ has a data type of string.

Closing Thoughts

In this tutorial, we explored different methods to check data types in MongoDB. Whether you prefer using MongoDB’s native operators or JavaScript’s typeof operator with db.eval(), understanding your data types is crucial for performing efficient operations and ensuring proper handling of your data.

Remember to choose the method that best suits your needs and be mindful of the implications when using certain approaches.

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