MongoDB offers powerful querying capabilities to retrieve documents from collections:
find(): Retrieves multiple documents from a collection.
Example: db.users.find({ age: { $gt: 25 } })
findOne(): Retrieves a single document from a collection.
Example: db.users.findOne({ name: 'John Doe' })
Query operators:
Comparison: $eq, $gt, $gte, $lt, $lte, $ne, $in, $nin
Example: db.users.find({ age: { $gte: 18, $lte: 30 } })
Logical: $and, $or, $not, $nor
Example: db.users.find({ $or: [{ age: { $lt: 18 } }, { age: { $gt: 60 } }] })
Element: $exists, $type
Example: db.users.find({ email: { $exists: true } })
Array: $all, $elemMatch, $size
Example: db.posts.find({ tags: { $all: ['mongodb', 'database'] } })
Projection: Specify which fields to return in the result documents.
Example: db.users.find({}, { name: 1, email: 1, _id: 0 })
Cursor methods:
sort(): Sorts the result set. Example: db.users.find().sort({ age: -1 })limit(): Limits the number of documents returned. Example: db.users.find().limit(5)skip(): Skips a specified number of documents. Example: db.users.find().skip(10)These methods can be combined for pagination: db.users.find().sort({ age: -1 }).skip(20).limit(10)