Projection for reducing data transfer in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is projection in MongoDB?

Projection in MongoDB means selecting only specific fields from documents to return, instead of the whole document. This helps reduce the amount of data sent over the network.

beginner

How do you exclude a field using projection in MongoDB?

You set the field to 0 in the projection object. For example, { fieldName: 0 } excludes that field from the result.

beginner

Why is using projection important when querying large documents?

Using projection reduces the size of data sent from the database to the application, which speeds up queries and saves bandwidth.

intermediate

Show a MongoDB query that returns only the 'name' and 'age' fields from a collection called 'users'.

db.users.find({}, { name: 1, age: 1, _id: 0 })<br>This query returns only 'name' and 'age' fields and excludes the '_id' field.

intermediate

Can you mix inclusion and exclusion in MongoDB projection?

No, except for the '_id' field, you cannot mix including some fields and excluding others in the same projection. You must choose either inclusion or exclusion.

What does setting a field to 1 in MongoDB projection do?

A Renames the field

B Excludes the field from the result

C Includes the field in the result

D Deletes the field from the database

Setting a field to 1 in projection means to include that field in the returned documents.

Which of these is a valid projection to exclude the 'password' field?

A { password: 1 }

B { password: 0 }

C { password: -1 }

D { password: true }

Setting a field to 0 excludes it from the result.

What happens if you do not specify projection in a MongoDB find query?

A All fields of the document are returned

B Only _id is returned

C No documents are returned

D An error occurs

By default, all fields of matching documents are returned.

Which field is included by default unless explicitly excluded in projection?

A _id

B name

C age

D password

The _id field is included by default unless explicitly excluded.

Can you include 'name' and exclude 'age' in the same projection?

A Yes, always

B Yes, but only in aggregation

C No, never

D No, except for _id field

MongoDB does not allow mixing inclusion and exclusion in projection except for the _id field.

Explain what projection is in MongoDB and why it helps reduce data transfer.

Think about sending only what you need instead of everything.

Describe how to write a MongoDB query that returns only certain fields and excludes others.

Remember inclusion means 1, exclusion means 0.