Querying Documents

Reading data from MongoDB is done with the find method. MongoDB's query language uses JSON-style filter objects and a rich set of operators that let you express almost any condition.

Basic find

find returns a cursor of all documents matching the filter. Without a filter it returns all documents in the collection.

// All documents
db.users.find()

// Documents where age equals 30
db.users.find({ age: 30 })

// Documents where city is "London"
db.users.find({ "address.city": "London" })

findOne returns the first matching document (or null if none match):

db.users.findOne({ email: "alice@example.com" })

Comparison Operators

MongoDB provides a full set of comparison operators:

db.products.find({ price: { $gt: 50 } })          // greater than
db.products.find({ price: { $gte: 50, $lte: 200 } }) // range
db.products.find({ stock: { $lt: 10 } })           // less than
db.products.find({ status: { $ne: "archived" } })  // not equal
db.products.find({ tag: { $in: ["sale", "new"] } }) // in array

Logical Operators

// AND — both conditions must be true
db.users.find({ age: { $gte: 18 }, country: "GB" })

// OR — at least one condition must be true
db.users.find({ $or: [{ age: { $lt: 18 } }, { verified: false }] })

// NOT
db.users.find({ age: { $not: { $gte: 65 } } })

Querying Arrays and Embedded Documents

MongoDB makes it easy to query into nested structures using dot notation:

// Documents where the hobbies array contains "cycling"
db.users.find({ hobbies: "cycling" })

// Documents where stats.views is greater than 1000
db.articles.find({ "stats.views": { $gt: 1000 } })

// $elemMatch — all conditions must be true for the same array element
db.orders.find({ items: { $elemMatch: { qty: { $gt: 5 }, price: { $lt: 20 } } } })

Projection

The second argument to find is a projection that controls which fields are returned. Use 1 to include and 0 to exclude:

// Return only name and email, exclude _id
db.users.find({}, { name: 1, email: 1, _id: 0 })

Sorting, Limiting, and Skipping

Cursors support chained methods for sorting and pagination:

db.products
  .find({ inStock: true })
  .sort({ price: 1 })    // 1 = ascending, -1 = descending
  .skip(20)
  .limit(10)

Regular Expressions

// Case-insensitive search for "mongo" in the title field
db.articles.find({ title: { $regex: /mongo/i } })