MongoDB Foundations·Documents with discipline

Queries, projections and arrays

A query is a document-shaped filter; a projection controls what comes back.

Beginner 14 min read Lesson 8 of 300 Challenge included

What you will be able to do

Use projection { title: 1, minutes: 1, _id: 0 } for list endpoints.
Use $elemMatch when multiple conditions must match the same array element.
Explain a query before assuming it is fast.

In plain English

MongoDB filters use field conditions and operators such as $gt, $in and $elemMatch. Projections reduce network and memory cost. Query arrays with intent: $elemMatch requires one element to satisfy all conditions.

query.jsJavaScript

db.lessons.find(
  {
    published: true,
    minutes: { $gte: 10, $lte: 20 },
    tags: { $in: ["javascript", "typescript"] }
  },
  { _id: 0, slug: 1, title: 1, minutes: 1 }
).sort({ minutes: -1 }).limit(10)

Your turn

Find short lessons

Medium

Find published lessons between 8 and 14 minutes and return only slug and title.

JAVASCRIPT · starter

db.lessons.find({})

Check your understanding before moving on.

Knowledge checkQuestion 1

Which operator requires one array element to satisfy several conditions?

Select an answer to continue

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Next: The aggregation pipeline

Lesson 8 of 300 · 0% of course