operators

Operators in MongoDB

MongoDB offers a variety of operators that help in querying, updating, and manipulating data. Below are key categories and commonly used operators:

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1. Query Operators

Used to filter documents in queries (find(), findOne()).

Operator	Description	Example Query
$eq	Equals	{ age: { $eq: 21 } }
$ne	Not equals	{ age: { $ne: 21 } }
$gt	Greater than	{ age: { $gt: 18 } }
$gte	Greater or equal	{ age: { $gte: 18 } }
$lt	Less than	{ age: { $lt: 18 } }
$lte	Less or equal	{ age: { $lte: 18 } }
$in	Matches any value	{ major: { $in: ["Physics", "Biology"] } }
$nin	Not in list	{ major: { $nin: ["Math", "History"] } }

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2. Logical Operators

Used to combine query conditions.

Operator	Description	Example Query
$and	Logical AND	{ $and: [ { age: { $gt: 18 } }, { major: "Physics" } ] }
$or	Logical OR	{ $or: [ { major: "Physics" }, { major: "Math" } ] }
$not	Negates condition	{ age: { $not: { $lt: 18 } } }
$nor	Logical NOR	{ $nor: [ { major: "Physics" }, { age: { $gt: 21 } } ] }

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3. Update Operators

Used to modify fields in documents.

Operator	Description	Example Query
$set	Updates a field	{ $set: { age: 22 } }
$unset	Removes a field	{ $unset: { major: "" } }
$inc	Increments a value	{ $inc: { age: 1 } }
$mul	Multiplies a value	{ $mul: { age: 2 } }
$rename	Renames a field	{ $rename: { "oldField": "newField" } }
$push	Adds to an array	{ $push: { courses: "Biology" } }
$pop	Removes from array	{ $pop: { courses: -1 } }
$pull	Removes by value	{ $pull: { courses: "Physics" } }

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4. Array Operators

Used for querying and updating arrays.

Operator	Description	Example Query
$all	Matches all values in an array	{ courses: { $all: ["Physics", "Math"] } }
$elemMatch	Matches array element	{ courses: { $elemMatch: { score: { $gt: 90 } } } }
$size	Matches array size	{ courses: { $size: 3 } }

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5. Element Operators

Used to match fields based on their existence or type.

Operator	Description	Example Query
$exists	Field existence	{ major: { $exists: true } }
$type	Matches data type	{ age: { $type: "int" } }

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6. Aggregation Operators

Used within aggregation pipelines.

Operator	Description	Example
$sum	Calculates sum	{ $sum: "$amount" }
$avg	Calculates average	{ $avg: "$score" }
$max	Finds maximum	{ $max: "$score" }
$min	Finds minimum	{ $min: "$score" }

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7. Comparison Operators in Aggregation

Used in aggregation queries.

Operator	Description	Example
$eq	Equals	{ $eq: ["$age", 21] }
$gt	Greater than	{ $gt: ["$age", 18] }

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Summary

• Query operators filter data ($eq, $gt, $in).
• Logical operators combine multiple conditions ($and, $or).
• Update operators modify data ($set, $push).
• Array and aggregation operators handle more complex data structures.

Let me know if you want more practical examples or clarifications! 😊