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Cheat Sheet: Type Conversion Operators

Conversion expressions, error handling, BSON type inspection, and migration examples.

$toString

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

Reference group: Conversion and type inspection

What it does

Converts supported values to strings; invalid conversions may error.

Syntax

{$toString: expression}

Use case

Export or integrate with string-based systems.

$toString: practical example

{ $project: { idText: { $toString: "$_id" } } }

💡 Explanation Converts supported values to strings; invalid conversions may error. When to use it Export or integrate with string-based systems.

Key Takeaways

Converts supported values to strings; invalid conversions may error.
Typical use: Export or integrate with string-based systems.

$toInt

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

Reference group: Conversion and type inspection

What it does

Converts compatible values to 32-bit integer.

Syntax

{$toInt: expression}

Use case

Normalize numeric strings.

Important notes

Invalid strings or out-of-range values can fail.

$toInt: practical example

{ $set: { quantityInt: { $toInt: "$quantityText" } } }

💡 Explanation Converts compatible values to 32-bit integer. When to use it Normalize numeric strings. Caution Invalid strings or out-of-range values can fail.

Key Takeaways

Converts compatible values to 32-bit integer.
Typical use: Normalize numeric strings.

$toLong

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

Reference group: Conversion and type inspection

What it does

Converts compatible values to 64-bit integer.

Syntax

{$toLong: expression}

Use case

Counts exceeding 32-bit range.

$toLong: practical example

{ $set: { viewsLong: { $toLong: "$viewsText" } } }

💡 Explanation Converts compatible values to 64-bit integer. When to use it Counts exceeding 32-bit range.

Key Takeaways

Converts compatible values to 64-bit integer.
Typical use: Counts exceeding 32-bit range.

$toDouble

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

Reference group: Conversion and type inspection

What it does

Converts compatible values to double precision.

Syntax

{$toDouble: expression}

Use case

Normalize numeric strings where floating-point semantics are acceptable.

$toDouble: practical example

{ $set: { score: { $toDouble: "$scoreText" } } }

💡 Explanation Converts compatible values to double precision. When to use it Normalize numeric strings where floating-point semantics are acceptable.

Key Takeaways

Converts compatible values to double precision.
Typical use: Normalize numeric strings where floating-point semantics are acceptable.

$toDecimal

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

Reference group: Conversion and type inspection

What it does

Converts compatible values to BSON Decimal128.

Syntax

{$toDecimal: expression}

Use case

Financial calculations needing decimal semantics.

$toDecimal: practical example

{ $set: { amount: { $toDecimal: "$amountText" } } }

💡 Explanation Converts compatible values to BSON Decimal128. When to use it Financial calculations needing decimal semantics.

Key Takeaways

Converts compatible values to BSON Decimal128.
Typical use: Financial calculations needing decimal semantics.

$toBool

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

Reference group: Conversion and type inspection

What it does

Converts supported values to boolean.

Syntax

{$toBool: expression}

Use case

Normalize boolean-like BSON values.

Important notes

Text false may convert to true as a non-empty string; explicitly map textual flags.

$toBool: practical example

{ $project: { flag: { $toBool: "$enabledValue" } } }

💡 Explanation Converts supported values to boolean. When to use it Normalize boolean-like BSON values. Caution Text false may convert to true as a non-empty string; explicitly map textual flags.

Key Takeaways

Converts supported values to boolean.
Typical use: Normalize boolean-like BSON values.

$toDate

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

Reference group: Conversion and type inspection

What it does

Converts supported date strings, numbers, or ObjectIds to BSON Date.

Syntax

{$toDate: expression}

Use case

Normalize timestamps.

$toDate: practical example

{ $set: { createdAtDate: { $toDate: "$createdAtText" } } }

💡 Explanation Converts supported date strings, numbers, or ObjectIds to BSON Date. When to use it Normalize timestamps.

Key Takeaways

Converts supported date strings, numbers, or ObjectIds to BSON Date.
Typical use: Normalize timestamps.

$toObjectId

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

Reference group: Conversion and type inspection

What it does

Converts valid 24-character hexadecimal strings to ObjectId.

Syntax

{$toObjectId: expression}

Use case

Migrate string references.

Important notes

Invalid strings cause conversion errors.

$toObjectId: practical example

{ $set: { customerObjectId: { $toObjectId: "$customerIdText" } } }

💡 Explanation Converts valid 24-character hexadecimal strings to ObjectId. When to use it Migrate string references. Caution Invalid strings cause conversion errors.

Key Takeaways

Converts valid 24-character hexadecimal strings to ObjectId.
Typical use: Migrate string references.

$convert

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

Reference group: Conversion and type inspection

What it does

General conversion with explicit error/null behavior.

Syntax

{$convert: { input, to, onError?, onNull? }}

Use case

Process dirty imports without failing the pipeline.

$convert: practical example

{ $set: { safeQty: { $convert: { input: "$qtyText", to: "int", onError: null, onNull: 0 } } } }

💡 Explanation General conversion with explicit error/null behavior. When to use it Process dirty imports without failing the pipeline.

Key Takeaways

General conversion with explicit error/null behavior.
Typical use: Process dirty imports without failing the pipeline.

$type

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

Reference group: Conversion and type inspection

What it does

Returns BSON type name; aggregation can report missing for an absent field.

Syntax

{$type: expression}

Use case

Audit mixed-type data.

$type: practical example

{ $project: { fieldType: { $type: "$price" } } }

💡 Explanation Returns BSON type name; aggregation can report missing for an absent field. When to use it Audit mixed-type data.

Key Takeaways

Returns BSON type name; aggregation can report missing for an absent field.
Typical use: Audit mixed-type data.

$toString

$toInt

$toLong

$toDouble

$toDecimal

$toBool

$toDate

$toObjectId

$convert

$type

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