What is Query Selectors/Query Operators?

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**$eq**: Matches values that are equal to a specified value. **$gt:** Matches values that are greater than a specified value. **$gte:** Matches values that are greater than or equal to a specified value. **$in:** Matches any of the values specified in an array. **$lt:** Matches values that are less than a specified value. **$lte:** Matches values that are less than or equal to a specified value. **$ne:** Matches all values that are not equal to a specified value. **$nin:** Matches none of the values specified in an array. const cursor = db.collection('inventory').find({ status: 'D' });

db.collection('inventory').find({ status: { $eq: 'D' } });

db.collection('inventory').find({ qty: { $gt: 20 } });

db.collection('inventory').find({ qty: { $gte: 20 } });

db.collection('inventory').find({ status: { $in: ['A', 'D'] } });

db.collection('inventory').find({ qty: { $lt: 50 } });

db.collection('inventory').find({ qty: { $lte: 50 } });

db.collection('inventory').find({ status: { $ne: 'A' } });

db.collection('inventory').find({ status: { $nin: ['B', 'C'] } }); **$and:** Joins query clauses with a logical AND returns all documents that match the conditions of both clauses. **$not:** Inverts the effect of a query predicate and returns documents that do not match the query predicate. **$nor:** Joins query clauses with a logical NOR returns all documents that fail to match both clauses. **$or:** Joins query clauses with a logical OR returns all documents that match the conditions of either clause. db.collection('inventory').find({ $and: [ { price: { $gt: 10 } }, { status: 'A' } ] });

db.collection('inventory').find({ $or: [ { qty: { $lt: 20 } }, { status: 'D' } ] });

db.collection('inventory').find({ price: { $not: { $gt: 50 } } });

db.collection('inventory').find({ $nor: [ { price: 1.99 }, { sale: true } ] }); db.collection('products').find({
  category: "Electronics", // Implicit AND
  $or: [
    { price: { $lt: 50 } },
    { onSale: true }
  ]
});

//explicit usage
db.collection('inventory').find({
  $and: [
    { $or: [{ qty: { $lt: 10 } }, { status: "D" }] },
    { $or: [{ price: { $gt: 50 } }, { featured: true }] }
  ]
}); **$all:** Matches arrays that contain all elements specified in the query. **$elemMatch:** Selects documents if element in the array field matches all the specified $elemMatch conditions. **$size:** Selects documents if the array field is a specified size. db.collection('users').find({ skills: { $all: ['Node.js', 'MongoDB'] } });

db.collection('inventory').find({ ratings: { $elemMatch: { score: { $gt: 8 }, user: 'Gaurav' } } });

db.collection('projects').find({ teamMembers: { $size: 3 } }); //$near
db.collection('places').find({
  location: {
    $near: {
      $geometry: { type: "Point", coordinates: [80.9462, 26.8467] },
      $maxDistance: 5000 // distance in meters
    }
  }
});

//$geoWithin
db.collection('regions').find({
  location: {
    $geoWithin: {
      $geometry: {
        type: "Polygon",
        coordinates: [[[80.1, 26.1], [80.2, 26.1], [80.2, 26.2], [80.1, 26.1]]]
      }
    }
  }
});

// $geoIntersects
db.collection('zones').find({
  area: {
    $geoIntersects: {
      $geometry: { type: "Point", coordinates: [80.9462, 26.8467] }
    }
  }
});

// Example using $centerSphere (standard for Earth-based geography)
db.collection('users').find({
  location: {
    $geoWithin: { $centerSphere: [ [80.9462, 26.8467], 10 / 6378.1 ] } 
    // 10km radius converted to radians (divide by Earth's radius)
  }
}); **$regex:** Provides regular expression capabilities for pattern matching strings in queries. **$mod:** Performs a modulo operation on the value of a field and selects documents with a specified result. **$text:** Performs a text search on the content of the fields indexed with a text index. This is much more powerful than $regex for large blocks of text. **$expr:** Allows the use of aggregation expressions within the query language. This is powerful because it lets you compare two different fields within the same document. **$jsonSchema:** Validates documents against a given JSON Schema. While usually used for collection validation, it can be used in a query. **$where:** Passes a string containing a JavaScript function or a full JavaScript function to the query system. // Finds items where the name contains 'phone' regardless of case
db.collection('products').find({ 
  name: { $regex: /phone/i } 
});

// Finds documents where qty % 4 == 0
db.collection('inventory').find({ 
  qty: { $mod: [4, 0] } 
});

// Requires a text index on the 'description' field
db.collection('articles').find({ 
  $text: { $search: "sustainable fashion" } 
});

db.collection('budgets').find({
  $expr: { $gt: ["$spent", "$budget"] }
});

db.collection('users').find({
  $jsonSchema: {
    required: ["email", "password"],
    properties: {
      email: { bsonType: "string", pattern: "@" }
    }
  }
});

db.collection('inventory').find({
  $where: function() {
    return (this.qty > 10 &&

What is Query Selectors/Query Operators?

In MongoDB, query selectors (also called query operators) are special expressions used to filter and retrieve documents from a collection based on specific conditions. They allow you to perform complex searches, comparisons, and logical operations on your data.

What is Query Selectors/Query Operators?

In MongoDB, query selectors (also called query operators) are special expressions used to filter and retrieve documents from a collection based on specific conditions. They allow you to perform complex searches, comparisons, and logical operations on your data.

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