How to Use $type Operator in MongoDB Queries

In MongoDB, use the $type operator in a query to filter documents based on the BSON data type of a field. It accepts either a string alias or a numeric code representing the data type, such as "string" or 2. This helps find documents where a field matches a specific type.

Syntax

The $type operator is used inside a query filter to specify the data type of a field you want to match. It can be used like this:

• { field: { $type: } }

Here, field is the name of the field to check, and <type> is either a string alias (like "string", "int") or a numeric BSON type code (like 2 for string, 16 for int).

json

{
  field: { $type: <type> }
}

Example

This example shows how to find documents in a collection where the age field is stored as an integer type.

mongodb

db.users.find({ age: { $type: "int" } })

Output

[
  { "_id": 1, "name": "Alice", "age": 30 },
  { "_id": 3, "name": "Charlie", "age": 25 }
]

Common Pitfalls

Common mistakes when using $type include:

• Using incorrect type names or codes that MongoDB does not recognize.
• Confusing string aliases with numeric codes; both are valid but must be correct.
• Expecting $type to convert types; it only filters by existing data types.

For example, this query is incorrect because "integer" is not a valid alias:

mongodb

db.users.find({ age: { $type: "integer" } })  // Incorrect

// Correct usage:
db.users.find({ age: { $type: "int" } })

Quick Reference

Type Alias	BSON Type Number	Description
double	1	64-bit floating point number
string	2	UTF-8 string
object	3	Embedded document
array	4	Array
binData	5	Binary data
undefined	6	Deprecated undefined
objectId	7	ObjectId
bool	8	Boolean
date	9	UTC datetime
null	10	Null value
regex	11	Regular expression
int	16	32-bit integer
long	18	64-bit integer
decimal	19	128-bit decimal floating point

Key Takeaways

Use $type in queries to filter documents by the BSON data type of a field.

You can specify the type using either string aliases or numeric BSON type codes.

Common aliases include "string", "int", "bool", and "date".

$type does not convert data types; it only matches existing types.

Check MongoDB documentation for valid type names and codes to avoid errors.