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Cheat Sheet: Update Operators

Field, numeric, array, positional, and upsert update operators with practical use cases.

$set

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Sets a field without replacing the whole document.

Syntax

{$set: { field: value }}

Use case

Update selected properties.

$set: practical example

db.users.updateOne({ _id: userId }, { $set: { "profile.theme": "dark" } })

💡 Explanation Sets a field without replacing the whole document. When to use it Update selected properties.

Key Takeaways

Sets a field without replacing the whole document.
Typical use: Update selected properties.

$unset

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Removes a field.

Syntax

{$unset: { field: "" }}

Use case

Remove deprecated properties.

$unset: practical example

db.users.updateOne({ _id: userId }, { $unset: { legacyField: "" } })

💡 Explanation Removes a field. When to use it Remove deprecated properties.

Key Takeaways

Removes a field.
Typical use: Remove deprecated properties.

$inc

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Atomically increments/decrements numeric fields.

Syntax

{$inc: { field: amount }}

Use case

Counters and inventory.

Important notes

Use a conditional filter to prevent invalid stock.

$inc: practical example

db.inventory.updateOne({ sku: "KB-1" }, { $inc: { stock: -1, sold: 1 } })

💡 Explanation Atomically increments/decrements numeric fields. When to use it Counters and inventory. Caution Use a conditional filter to prevent invalid stock.

Key Takeaways

Atomically increments/decrements numeric fields.
Typical use: Counters and inventory.

$mul

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Multiplies existing numeric fields by a factor.

Syntax

{$mul: { field: factor }}

Use case

Controlled scaling.

$mul: practical example

db.metrics.updateMany({}, { $mul: { score: 1.1 } })

💡 Explanation Multiplies existing numeric fields by a factor. When to use it Controlled scaling.

Key Takeaways

Multiplies existing numeric fields by a factor.
Typical use: Controlled scaling.

$min/$max

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Updates only when the provided value is lower or higher, respectively.

Syntax

{$min: { field: value }} / {$max: { field: value }}

Use case

Maintain high/low-water marks.

$min/$max: practical example

db.metrics.updateOne({ _id: id }, { $max: { highScore: newScore } })

💡 Explanation Updates only when the provided value is lower or higher, respectively. When to use it Maintain high/low-water marks.

Key Takeaways

Updates only when the provided value is lower or higher, respectively.
Typical use: Maintain high/low-water marks.

$rename

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Renames a field.

Syntax

{$rename: { oldName: newName }}

Use case

Migrate a field name.

Important notes

Plan compatibility with old readers and validators.

$rename: practical example

db.users.updateMany({}, { $rename: { "profile.nick": "profile.nickname" } })

💡 Explanation Renames a field. When to use it Migrate a field name. Caution Plan compatibility with old readers and validators.

Key Takeaways

Renames a field.
Typical use: Migrate a field name.

$currentDate

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Sets current date or a BSON timestamp with the appropriate option.

Syntax

{$currentDate: { field: true }}

Use case

Maintain modification timestamps.

$currentDate: practical example

db.orders.updateOne({ _id: orderId }, { $currentDate: { updatedAt: true } })

💡 Explanation Sets current date or a BSON timestamp with the appropriate option. When to use it Maintain modification timestamps.

Key Takeaways

Sets current date or a BSON timestamp with the appropriate option.
Typical use: Maintain modification timestamps.

$setOnInsert

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Applies values only when an upsert inserts a new document.

Syntax

{$setOnInsert: { field: value }}

Use case

Initialize creation metadata.

$setOnInsert: practical example

db.settings.updateOne({ _id: "theme" }, { $set: { enabled: true }, $setOnInsert: { createdAt: new Date() } }, { upsert: true })

💡 Explanation Applies values only when an upsert inserts a new document. When to use it Initialize creation metadata.

Key Takeaways

Applies values only when an upsert inserts a new document.
Typical use: Initialize creation metadata.

$push modifiers

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Appends values and optionally sorts, positions, or caps the array.

Syntax

{$push: { arr: { $each, $sort?, $slice?, $position? } }}

Use case

Maintain bounded recent items.

$push modifiers: practical example

db.users.updateOne({ _id: userId }, { $push: { recent: { $each: [entry], $sort: { at: -1 }, $slice: 10 } } })

💡 Explanation Appends values and optionally sorts, positions, or caps the array. When to use it Maintain bounded recent items.

Key Takeaways

Appends values and optionally sorts, positions, or caps the array.
Typical use: Maintain bounded recent items.

$addToSet

Reference type:Cheat sheetFormat:Syntax + example + use case

Reference group: Update operator families

What it does

Adds only if an equal value is absent.

Syntax

{$addToSet: { array: value }}

Use case

Set-like roles or tags.

$addToSet: practical example

db.users.updateOne({ _id: userId }, { $addToSet: { permissions: "reports:read" } })

💡 Explanation Adds only if an equal value is absent. When to use it Set-like roles or tags.

Key Takeaways

Adds only if an equal value is absent.
Typical use: Set-like roles or tags.

$set

$unset

$inc

$mul

$min/$max

$rename

$currentDate

$setOnInsert

$push modifiers

$addToSet

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