Projection

Introduction

Projection shapes the returned documents — picking fields, slicing arrays, or computing values. Smaller payloads = faster network = happier UI.

Syntax reference

db.users.find({}, { name: 1, email: 1, _id: 0 });

// Array slice
db.posts.find({}, { comments: { $slice: 5 } });

// Computed (aggregation)
db.users.aggregate([{ $project: { fullName: { $concat: ["$first"," ","$last"] } } }]);

Real-world use

List endpoints should always project — never return the full document for a row in a table.

Best practices

• Project explicitly; don't rely on SELECT * habits.
• Combine with covering indexes for zero-fetch queries.