Mongodb Operators

 MongoDB operators are special reserved keywords used to perform various operations in MongoDB queries. They are categorized into several groups based on their functionality. Here's a breakdown:

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1. Comparison Operators

These are used to compare field values in queries.

Operator	Description	Example
$eq	Matches values equal to a specified value.	{ age: { $eq: 25 } }
$ne	Matches values not equal to a specified value.	{ age: { $ne: 25 } }
$gt	Matches values greater than a specified value.	{ age: { $gt: 25 } }
$gte	Matches values greater than or equal to a specified value.	{ age: { $gte: 25 } }
$lt	Matches values less than a specified value.	{ age: { $lt: 25 } }
$lte	Matches values less than or equal to a specified value.	{ age: { $lte: 25 } }
$in	Matches any value in a specified array.	{ age: { $in: [25, 30, 35] } }
$nin	Matches none of the values in a specified array.	{ age: { $nin: [25, 30, 35] } }

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2. Logical Operators

These are used to combine multiple conditions.

Operator	Description	Example
$and	Joins queries with a logical AND.	{ $and: [ { age: { $gt: 20 } }, { age: { $lt: 30 } } ] }
$or	Joins queries with a logical OR.	{ $or: [ { age: { $lt: 20 } }, { age: { $gt: 30 } } ] }
$not	Inverts a query condition.	{ age: { $not: { $gt: 25 } } }
$nor	Matches documents that fail all the conditions.	{ $nor: [ { age: { $lt: 20 } }, { age: { $gt: 30 } } ] }

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3. Element Operators

These query for fields based on the presence or absence of data.

Operator	Description	Example
$exists	Checks if a field exists or not.	{ name: { $exists: true } }
$type	Matches fields of a specific BSON type.	{ age: { $type: "int" } }

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4. Array Operators

These are used to work with arrays.

Operator	Description	Example
$all	Matches arrays containing all specified elements.	{ tags: { $all: ["sports", "music"] } }
$elemMatch	Matches arrays containing at least one element that matches all specified conditions.	{ scores: { $elemMatch: { $gte: 80, $lte: 90 } } }
$size	Matches arrays with the specified number of elements.	{ tags: { $size: 3 } }

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5. Evaluation Operators

These are used to apply functions or custom conditions.

Operator	Description	Example
$regex	Matches strings with a regular expression.	{ name: { $regex: /^A/ } }
$expr	Allows using aggregation expressions in queries.	{ $expr: { $gt: ["$age", 30] } }
$jsonSchema	Validates documents against a JSON schema.	{ $jsonSchema: { properties: { age: { type: "number" } } } }

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6. Update Operators

These modify documents during an update operation.

Operator	Description	Example
$set	Sets the value of a field.	{ $set: { name: "John" } }
$unset	Removes a field.	{ $unset: { name: "" } }
$inc	Increments a field by a specified value.	{ $inc: { age: 1 } }
$rename	Renames a field.	{ $rename: { oldName: "newName" } }
$push	Adds an element to an array.	{ $push: { tags: "newTag" } }
$pull	Removes elements from an array.	{ $pull: { tags: "oldTag" } }
$addToSet	Adds a value to an array if it doesn’t exist.	{ $addToSet: { tags: "uniqueTag" } }

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7. Aggregation Operators

These are used in aggregation pipelines.

Operator	Description	Example
$match	Filters documents to pass only those that match the condition.	{ $match: { age: { $gte: 30 } } }
$group	Groups documents by a specified key and performs aggregations.	{ $group: { _id: "$city", total: { $sum: 1 } } }
$project	Shapes the documents to return specific fields.	{ $project: { name: 1, age: 1 } }
$sort	Sorts the documents.	{ $sort: { age: -1 } }
$lookup	Performs a join with another collection.	{ $lookup: { from: "orders", localField: "userId", foreignField: "_id", as: "userOrders" } }

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This is a broad overview of MongoDB operators. Let me know if you'd like more details or examples for any specific operator!