Excluding fields from results in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Excluding a single field from MongoDB query results

Given a collection users with documents containing name, age, and email, which query excludes the email field from the results?

MongoDB

db.users.find({}, {email: 0})

A db.users.find({}, {email: 0})

B db.users.find({}, {email: 1})

C db.users.find({}, {email: false})

D db.users.find({}, {email: null})

💡 Hint

Use 0 to exclude a field in the projection document.

In MongoDB, setting a field to 0 in the projection excludes it from the results. Setting it to 1 includes it. Using false or null is invalid syntax.

❓ query_result

intermediate

Excluding multiple fields in MongoDB query results

Which query excludes both password and ssn fields from the accounts collection results?

MongoDB

db.accounts.find({}, {password: 0, ssn: 0})

A db.accounts.find({}, {password: null, ssn: null})

B db.accounts.find({}, {password: 1, ssn: 1})

C db.accounts.find({}, {password: false, ssn: false})

D db.accounts.find({}, {password: 0, ssn: 0})

💡 Hint

Exclude multiple fields by setting each to 0 in the projection.

Setting multiple fields to 0 in the projection excludes them all from the results. Including them with 1 would only show those fields.

📝 Syntax

advanced

Identify the invalid MongoDB projection syntax

Which of the following MongoDB queries will cause a syntax error due to incorrect projection?

A db.products.find({}, {price: false, name: 0})

B db.products.find({}, {price: 1, name: 0})

C db.products.find({}, {price: 0, name: 1})

D db.products.find({}, {price: 0, name: 0})

💡 Hint

Projection values must be 0 or 1, not false.

MongoDB projection only accepts 0 or 1 to exclude or include fields. Using false causes a syntax error.

🧠 Conceptual

advanced

Understanding exclusion and inclusion in MongoDB projections

What happens if you try to exclude one field and include another in the same MongoDB projection, like {field1: 0, field2: 1}?

A MongoDB excludes both fields regardless of the values.

B MongoDB excludes field1 and includes field2 without error.

C MongoDB throws an error because you cannot mix inclusion and exclusion except for _id.

D MongoDB ignores the exclusion and includes all fields.

💡 Hint

MongoDB projection rules restrict mixing inclusion and exclusion.

MongoDB does not allow mixing inclusion and exclusion in the same projection except for the _id field. Doing so causes an error.

❓ optimization

expert

Optimizing MongoDB queries by excluding large fields

You have a collection videos where each document has a large videoData field. To improve query speed when listing videos, which projection is best?

A db.videos.find({}, {videoData: 1})

B db.videos.find({}, {videoData: 0})

C db.videos.find({}, {videoData: null})

D db.videos.find({}, {videoData: false})

💡 Hint

Exclude large fields to reduce data transfer and improve speed.

Excluding the large videoData field with videoData: 0 reduces the amount of data sent, improving query speed. Including it or using invalid values does not help.