MongoDb Operators

MongoDB operators in Node.js can be categorized into various groups like comparison, logical, array, update, element, and more. Below is a comprehensive list of commonly used MongoDB operators, along with their explanations, examples, and expected outputs:

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Comparison Operators

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Logical Operators

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Element Operators

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Array Operators

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Update Operators

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These are some key operators frequently used in Node.js applications with MongoDB. Let me know if you'd like to explore more examples or specific scenarios!

Below is a detailed explanation of all MongoDB operators, categorized by their purpose. Each section provides examples, scenarios where you would use the operator, and the expected output to give you a comprehensive understanding.

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1. Comparison Operators

These are used to compare field values in documents.

$eq - Equal

Matches values equal to a specified value.
Example:

db.collection.find({ age: { $eq: 25 } });

Input Data:

[
  { "_id": 1, "age": 25 },
  { "_id": 2, "age": 30 }
]

Output:

[ { "_id": 1, "age": 25 } ]

Use Case: Finding users of a specific age.

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$ne - Not Equal

Matches values not equal to a specified value.
Example:

db.collection.find({ age: { $ne: 25 } });

Output:

[ { "_id": 2, "age": 30 } ]

Use Case: Excluding certain values from a query result.

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$gt - Greater Than

Matches values greater than a specified value.
Example:

db.collection.find({ age: { $gt: 25 } });

Output:

[ { "_id": 2, "age": 30 } ]

Use Case: Finding records with numerical values above a threshold.

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$gte - Greater Than or Equal

Matches values greater than or equal to a specified value.
Example:

db.collection.find({ age: { $gte: 25 } });

Output:

[ { "_id": 1, "age": 25 }, { "_id": 2, "age": 30 } ]

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$lt - Less Than

Matches values less than a specified value.
Example:

db.collection.find({ age: { $lt: 30 } });

Output:

[ { "_id": 1, "age": 25 } ]

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$lte - Less Than or Equal

Matches values less than or equal to a specified value.
Example:

db.collection.find({ age: { $lte: 25 } });

Output:

[ { "_id": 1, "age": 25 } ]

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$in - Matches Any in a List

Matches documents where the value is in the provided array.
Example:

db.collection.find({ age: { $in: [25, 30] } });

Output:

[ { "_id": 1, "age": 25 }, { "_id": 2, "age": 30 } ]

Use Case: Querying for multiple possible values.

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$nin - Matches None in a List

Matches documents where the value is not in the provided array.
Example:

db.collection.find({ age: { $nin: [25, 30] } });

Output:

[ { "_id": 3, "age": 40 } ]

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2. Logical Operators

These are used to combine multiple conditions in a query.

$and - Logical AND

Matches documents that satisfy all the specified conditions.
Example:

db.collection.find({ $and: [{ age: { $gte: 25 } }, { age: { $lt: 30 } }] });

Output:

[ { "_id": 1, "age": 25 } ]

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$or - Logical OR

Matches documents that satisfy at least one condition.
Example:

db.collection.find({ $or: [{ age: { $lt: 20 } }, { age: { $gt: 30 } }] });

Output:

[ { "_id": 3, "age": 40 } ]

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$not - Logical NOT

Inverts the query condition.
Example:

db.collection.find({ age: { $not: { $gte: 30 } } });

Output:

[ { "_id": 1, "age": 25 } ]

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$nor - Logical NOR

Matches documents that fail to match all conditions.
Example:

db.collection.find({ $nor: [{ age: { $lt: 20 } }, { age: { $gte: 30 } }] });

Output:

[ { "_id": 1, "age": 25 } ]

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3. Update Operators

These are used for modifying documents.

$set - Sets the Value of a Field

Example:

db.collection.updateOne({ _id: 1 }, { $set: { name: "John" } });

Input:

{ "_id": 1, "name": "Doe" }

Output:

{ "_id": 1, "name": "John" }

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$unset - Removes a Field

Example:

db.collection.updateOne({ _id: 1 }, { $unset: { name: "" } });

Output:

{ "_id": 1 }

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$inc - Increment a Numeric Field

Example:

db.collection.updateOne({ _id: 1 }, { $inc: { count: 1 } });

Input:

{ "_id": 1, "count": 5 }

Output:

{ "_id": 1, "count": 6 }

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$push - Add to an Array

Example:

db.collection.updateOne({ _id: 1 }, { $push: { tags: "new" } });

Output:

{ "_id": 1, "tags": ["tech", "new"] }

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$pull - Remove from an Array

Example:

db.collection.updateOne({ _id: 1 }, { $pull: { tags: "tech" } });

Output:

{ "_id": 1, "tags": [] }

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4. Array Operators

$all - Matches Arrays with All Specified Elements

Example:

db.collection.find({ tags: { $all: ["tech", "blog"] } });

Output:

[ { "_id": 1, "tags": ["tech", "blog"] } ]

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$size - Matches Arrays of a Specific Size

Example:

db.collection.find({ tags: { $size: 2 } });

Output:

[ { "_id": 1, "tags": ["tech", "blog"] } ]

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$elemMatch - Matches a Single Element in an Array

Example:

db.collection.find({ scores: { $elemMatch: { $gte: 80, $lt: 90 } } });

Input:

{ "_id": 1, "scores": [50, 85, 95] }

Output:

[ { "_id": 1, "scores": [50, 85, 95] } ]

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These operators provide you with powerful tools for querying and manipulating MongoDB documents. If you have a specific use case or need further clarification, let me know!