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Cheat Sheet: Query Operators

Filters, comparisons, logical predicates, field existence/type checks, array predicates, and expression-based queries.

$eq / $ne

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

Reference group: Query filter operators

What it does

Equality and inequality; direct equality syntax is often shorter.

Syntax

{ field: { $eq: value } } / { field: { $ne: value } }

Use case

Filter exact values or exclude a value.

$eq / $ne: practical example

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

💡 Explanation Equality and inequality; direct equality syntax is often shorter. When to use it Filter exact values or exclude a value.

Key Takeaways

Equality and inequality; direct equality syntax is often shorter.
Typical use: Filter exact values or exclude a value.

$gt / $gte / $lt / $lte

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

Reference group: Query filter operators

What it does

Range comparisons use BSON comparison semantics.

Syntax

{ field: { $gte: value } }

Use case

Filter prices, dates, or thresholds.

$gt /$gte /$lt /$lte: practical example

db.orders.find({ total: { $gte: 1000, $lt: 5000 } })

💡 Explanation Range comparisons use BSON comparison semantics. When to use it Filter prices, dates, or thresholds.

Key Takeaways

Range comparisons use BSON comparison semantics.
Typical use: Filter prices, dates, or thresholds.

$and /$or /$nor

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

Reference group: Query filter operators

What it does

Combines predicates; separate fields in one object are implicitly ANDed.

Syntax

{$or: [{...}, {...}]}

Use case

Express alternatives.

$and /$or /$nor: practical example

db.users.find({ $or: [{ role: "admin" }, { permissions: "manage" }] })

💡 Explanation Combines predicates; separate fields in one object are implicitly ANDed. When to use it Express alternatives.

Key Takeaways

Combines predicates; separate fields in one object are implicitly ANDed.
Typical use: Express alternatives.

$exists

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

Reference group: Query filter operators

What it does

Tests field presence even when its value is null.

Syntax

{ field: { $exists: true } }

Use case

Distinguish missing from null.

$exists: practical example

db.users.find({ middleName: { $exists: false } })

💡 Explanation Tests field presence even when its value is null. When to use it Distinguish missing from null.

Key Takeaways

Tests field presence even when its value is null.
Typical use: Distinguish missing from null.

$type

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

Reference group: Query filter operators

What it does

Matches a specified BSON type.

Syntax

{ field: { $type: "string" } }

Use case

Audit type drift.

$type: practical example

db.products.find({ price: { $type: "string" } })

💡 Explanation Matches a specified BSON type. When to use it Audit type drift.

Key Takeaways

Matches a specified BSON type.
Typical use: Audit type drift.

$regex

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

Reference group: Query filter operators

What it does

Matches strings using regular expressions.

Syntax

{ field: { $regex: pattern, $options: flags } }

Use case

Pattern matching and cleanup.

Important notes

Unanchored/case-insensitive regex may be inefficient.

$regex: practical example

db.users.find({ email: { $regex: "@example\\.com$", $options: "i" } })

💡 Explanation Matches strings using regular expressions. When to use it Pattern matching and cleanup. Caution Unanchored/case-insensitive regex may be inefficient.

Key Takeaways

Matches strings using regular expressions.
Typical use: Pattern matching and cleanup.

$expr

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

Reference group: Query filter operators

What it does

Allows aggregation expressions inside query filters.

Syntax

{$expr: expression}

Use case

Compare fields in one document.

$expr: practical example

db.inventory.find({ $expr: { $lt: ["$available", "$reorderPoint"] } })

💡 Explanation Allows aggregation expressions inside query filters. When to use it Compare fields in one document.

Key Takeaways

Allows aggregation expressions inside query filters.
Typical use: Compare fields in one document.

$mod

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

Reference group: Query filter operators

What it does

Matches numeric values with a given remainder.

Syntax

{ field: { $mod: [divisor, remainder] } }

Use case

Select even/odd counters.

$mod: practical example

db.jobs.find({ attempt: { $mod: [2, 0] } })

💡 Explanation Matches numeric values with a given remainder. When to use it Select even/odd counters.

Key Takeaways

Matches numeric values with a given remainder.
Typical use: Select even/odd counters.

$elemMatch

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

Reference group: Query filter operators

What it does

Requires one array element to satisfy all inner conditions.

Syntax

{ array: { $elemMatch: { ... } } }

Use case

Filter embedded items.

$elemMatch: practical example

db.orders.find({ items: { $elemMatch: { sku: "KB-1", quantity: { $gte: 2 } } } })

💡 Explanation Requires one array element to satisfy all inner conditions. When to use it Filter embedded items.

Key Takeaways

Requires one array element to satisfy all inner conditions.
Typical use: Filter embedded items.

$all

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

Reference group: Query filter operators

What it does

Requires all listed values in an array.

Syntax

{ array: { $all: [values] } }

Use case

Find records with all labels.

$all: practical example

db.articles.find({ tags: { $all: ["mongodb", "indexing"] } })

💡 Explanation Requires all listed values in an array. When to use it Find records with all labels.

Key Takeaways

Requires all listed values in an array.
Typical use: Find records with all labels.

$eq / $ne

$gt / $gte / $lt / $lte

$and /$or /$nor

$exists

$type

$regex

$expr

$mod

$elemMatch

$all

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