MongoDB Update Operators

Modify documents efficiently with update operators

✏️ What are Update Operators?

Update operators modify existing documents in MongoDB. They let you change field values, add new fields, remove fields, or update arrays without replacing the entire document. 


// Increase product price by 10
db.products.updateOne(
    { _id: 1 },
    { $inc: { price: 10 } }
)

Field Update Operators

Field operators modify specific fields in documents. Use them to set values, increment numbers, rename fields, or remove fields entirely.

📝

$set

Sets the value of a field 

db.users.updateOne(
    { name: "John" },
    { $set: { age: 30 } }
)
🗑️

$unset

Removes a field from document 

db.users.updateOne(
    { name: "John" },
    { $unset: { age: "" } }
)
➕

$inc

Increments field by specified value 

db.products.updateOne(
    { _id: 1 },
    { $inc: { views: 1 } }
)
✖️

$mul

Multiplies field by specified value 

db.products.updateOne(
    { _id: 1 },
    { $mul: { price: 1.1 } }
)

🔹 $set Operator

The $set operator replaces the value of a field with the specified value. If the field doesn't exist, it creates it.

🔸 Basic Usage 

// Update single field
db.users.updateOne(
    { name: "Alice" },
    { $set: { email: "[email protected]" } }
)

// Update multiple fields
db.users.updateOne(
    { name: "Bob" },
    { 
        $set: { 
            email: "[email protected]",
            age: 28,
            city: "New York"
        } 
    }
)

Before: 

{ "_id": 1, "name": "Bob", "age": 25 }

After: 

{ "_id": 1, "name": "Bob", "age": 28, "email": "[email protected]", "city": "New York" }

🔹 $inc Operator

The $inc operator increments a numeric field by a specified value. Use negative numbers to decrement.

🔸 Increment Examples 

// Increase product stock by 50
db.products.updateOne(
    { _id: 1 },
    { $inc: { stock: 50 } }
)

// Decrease price by 5 (negative increment)
db.products.updateOne(
    { _id: 1 },
    { $inc: { price: -5 } }
)

// Increment multiple fields
db.posts.updateOne(
    { _id: 1 },
    { 
        $inc: { 
            views: 1,
            likes: 1
        } 
    }
)

Before: 

{ "_id": 1, "title": "My Post", "views": 100, "likes": 5 }

After: 

{ "_id": 1, "title": "My Post", "views": 101, "likes": 6 }

🔹 Array Update Operators

Array operators add, remove, or modify elements in array fields without replacing the entire array.

🔸 $push Operator 

// Add item to array
db.users.updateOne(
    { name: "John" },
    { $push: { hobbies: "reading" } }
)

// Add multiple items
db.users.updateOne(
    { name: "John" },
    { $push: { hobbies: { $each: ["gaming", "cooking"] } } }
)

Before: 

{ "_id": 1, "name": "John", "hobbies": ["sports"] }

After: 

{ "_id": 1, "name": "John", "hobbies": ["sports", "reading", "gaming", "cooking"] }

🔸 $pull Operator 

// Remove specific value from array
db.users.updateOne(
    { name: "John" },
    { $pull: { hobbies: "gaming" } }
)

// Remove multiple values
db.products.updateOne(
    { _id: 1 },
    { $pull: { tags: { $in: ["old", "deprecated"] } } }
)

🔸 $pop Operator 

// Remove last element (-1 for first)
db.users.updateOne(
    { name: "John" },
    { $pop: { hobbies: 1 } }
)

// Remove first element
db.users.updateOne(
    { name: "John" },
    { $pop: { hobbies: -1 } }
)

🔹 $addToSet Operator

The $addToSet operator adds a value to an array only if it doesn't already exist, preventing duplicates. 

// Add unique tag
db.posts.updateOne(
    { _id: 1 },
    { $addToSet: { tags: "mongodb" } }
)

// Add multiple unique values
db.posts.updateOne(
    { _id: 1 },
    { 
        $addToSet: { 
            tags: { $each: ["database", "nosql", "mongodb"] } 
        } 
    }
)

Before: 

{ "_id": 1, "title": "Post", "tags": ["mongodb", "database"] }

After (mongodb already exists, nosql added): 

{ "_id": 1, "title": "Post", "tags": ["mongodb", "database", "nosql"] }

🔹 $rename Operator

The $rename operator changes the name of a field in documents. 

// Rename single field
db.users.updateMany(
    {},
    { $rename: { "phone": "phoneNumber" } }
)

// Rename multiple fields
db.products.updateMany(
    {},
    { 
        $rename: { 
            "desc": "description",
            "qty": "quantity"
        } 
    }
)

Before: 

{ "_id": 1, "name": "Product", "desc": "Great item", "qty": 100 }

After: 

{ "_id": 1, "name": "Product", "description": "Great item", "quantity": 100 }

🔹 Practical Examples

Combine operators for complex updates:

Example 1: Update Product Inventory 

// Decrease stock, increase sold count, update status
db.products.updateOne(
    { _id: 1 },
    {
        $inc: { stock: -1, soldCount: 1 },
        $set: { lastSold: new Date() },
        $push: { 
            salesHistory: { 
                date: new Date(), 
                quantity: 1 
            } 
        }
    }
)

Example 2: Update User Profile 

// Update profile and add new skill
db.users.updateOne(
    { email: "[email protected]" },
    {
        $set: { 
            lastLogin: new Date(),
            status: "active"
        },
        $addToSet: { skills: "MongoDB" },
        $inc: { loginCount: 1 }
    }
)

🧠 Test Your Knowledge

Which operator adds a value to an array without creating duplicates?