MongoDB Query Operators

Comparison Operators

Comparison operators let you compare values in your queries. They work with numbers, strings, and dates to filter documents based on conditions.

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

db.products.find({ status: { $ne: "sold" } })

db.users.find({ age: { $gt: 18 } })

db.products.find({ price: { $lt: 50 } })

🔹 Logical Operators

Logical operators combine multiple conditions in your queries. Use them to create complex filters with AND, OR, and NOT logic.

🔸 $and Operator

// Find products that are cheap AND in stock
db.products.find({
    $and: [
        { price: { $lt: 100 } },
        { inStock: true }
    ]
})

{ "_id": 1, "name": "Keyboard", "price": 45, "inStock": true }
{ "_id": 2, "name": "Mouse", "price": 25, "inStock": true }

🔸 $or Operator

// Find users from USA OR Canada
db.users.find({
    $or: [
        { country: "USA" },
        { country: "Canada" }
    ]
})

{ "_id": 1, "name": "John", "country": "USA" }
{ "_id": 2, "name": "Sarah", "country": "Canada" }

🔸 $not Operator

// Find products NOT expensive
db.products.find({
    price: { $not: { $gt: 100 } }
})

🔹 Element Operators

Element operators check if fields exist or match specific types in your documents.

🔸 $exists Operator

// Find users who have email field
db.users.find({ email: { $exists: true } })

// Find users without phone number
db.users.find({ phone: { $exists: false } })

{ "_id": 1, "name": "Alice", "email": "[email protected]" }
{ "_id": 2, "name": "Bob", "email": "[email protected]" }

🔸 $type Operator

// Find documents where age is a number
db.users.find({ age: { $type: "number" } })

// Find documents where tags is an array
db.posts.find({ tags: { $type: "array" } })

🔹 Array Operators

Array operators help you query documents with array fields, checking for specific values or array sizes.

🔸 $in Operator

// Find products in specific categories
db.products.find({
    category: { $in: ["Electronics", "Books", "Toys"] }
})

{ "_id": 1, "name": "Laptop", "category": "Electronics" }
{ "_id": 2, "name": "Novel", "category": "Books" }

🔸 $all Operator

// Find posts with all specified tags
db.posts.find({
    tags: { $all: ["mongodb", "database"] }
})

🔸 $size Operator

// Find users with exactly 3 hobbies
db.users.find({
    hobbies: { $size: 3 }
})

🔹 String Operators

Search text fields using pattern matching with regular expressions.

🔸 $regex Operator

// Find users whose name starts with "J"
db.users.find({
    name: { $regex: /^J/, $options: "i" }
})

// Find products containing "phone" (case-insensitive)
db.products.find({
    name: { $regex: /phone/i }
})

{ "_id": 1, "name": "iPhone 15" }
{ "_id": 2, "name": "Samsung Phone" }

🔹 Practical Examples

Combine multiple operators for powerful queries:

// Find affordable electronics in stock
db.products.find({
    $and: [
        { category: "Electronics" },
        { price: { $gte: 50, $lte: 500 } },
        { inStock: true },
        { rating: { $gte: 4.0 } }
    ]
})

// Find active users from specific countries
db.users.find({
    $and: [
        { status: "active" },
        { country: { $in: ["USA", "UK", "Canada"] } },
        { age: { $gte: 18, $lte: 65 } },
        { email: { $exists: true } }
    ]
})