Query Operators in MongoDB

Query operators in MongoDB are used to specify conditions for matching documents in a collection. They allow you to perform complex queries and retrieve documents based on various criteria. MongoDB provides a rich set of query operators for different types of operations.

Here’s an overview of some commonly used query operators:

1. $eq (Equal To)

The $eq operator matches documents where the value of a field is equal to the specified value.

Syntax:

db.collection.find({ field: { $eq: value } })

Example: Find documents where the status field is equal to "active":

db.users.find({ status: { $eq: "active" } })

This is equivalent to:

db.users.find({ status: "active" })

2. $ne (Not Equal To)

The $ne operator matches documents where the value of a field is not equal to the specified value.

Syntax:

db.collection.find({ field: { $ne: value } })

Example: Find documents where the age field is not equal to 30:

db.users.find({ age: { $ne: 30 } })

3. $gt (Greater Than)

The $gt operator matches documents where the value of a field is greater than the specified value.

Syntax:

db.collection.find({ field: { $gt: value } })

Example: Find documents where the age field is greater than 25:

db.users.find({ age: { $gt: 25 } })

4. $lt (Less Than)

The $lt operator matches documents where the value of a field is less than the specified value.

Syntax:

db.collection.find({ field: { $lt: value } })

Example: Find documents where the price field is less than 100:

db.products.find({ price: { $lt: 100 } })

5. $gte (Greater Than or Equal To)

The $gte operator matches documents where the value of a field is greater than or equal to the specified value.

Syntax:

db.collection.find({ field: { $gte: value } })

Example: Find documents where the age field is greater than or equal to 30:

db.users.find({ age: { $gte: 30 } })

6. $lte (Less Than or Equal To)

The $lte operator matches documents where the value of a field is less than or equal to the specified value.

Syntax:

db.collection.find({ field: { $lte: value } })

Example: Find documents where the price field is less than or equal to 150:

db.products.find({ price: { $lte: 150 } })

7. $in

The $in operator matches documents where the value of a field is in the specified array of values.

Syntax:

db.collection.find({ field: { $in: [value1, value2, ...] } })

Example: Find documents where the status field is either "active" or "pending":

db.orders.find({ status: { $in: ["active", "pending"] } })

8. $nin (Not In)

The $nin operator matches documents where the value of a field is not in the specified array of values.

Syntax:

db.collection.find({ field: { $nin: [value1, value2, ...] } })

Example: Find documents where the category field is neither "electronics" nor "furniture":

db.products.find({ category: { $nin: ["electronics", "furniture"] } })

9. $exists

The $exists operator matches documents where a field exists or does not exist.

Syntax:

db.collection.find({ field: { $exists: true } })

Example: Find documents where the email field exists:

db.users.find({ email: { $exists: true } })

10. $regex

The $regex operator matches documents where the value of a field matches a specified regular expression.

Syntax:

db.collection.find({ field: { $regex: pattern, $options: 'i' } })

• pattern: The regular expression pattern.
• $options: Optional flags (e.g., 'i' for case-insensitive).

Example: Find documents where the name field contains "john" (case-insensitive):

db.users.find({ name: { $regex: /john/, $options: 'i' } })

11. $type

The $type operator matches documents where the value of a field is of a specified BSON data type.

Syntax:

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

• type: The BSON data type (e.g., 1 for double, 2 for string).

Example: Find documents where the age field is of type number:

db.users.find({ age: { $type: 'number' } })