Boolean and null types in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What values can a Boolean type hold in MongoDB?

A Boolean type in MongoDB can hold only two values: true or false. These represent simple yes/no or on/off states.

beginner

What does the null type represent in MongoDB?

The null type in MongoDB represents the absence of a value or a missing field. It means the field exists but has no value assigned.

intermediate

How do you query documents where a field is null in MongoDB?

Use { fieldName: null } in your query to find documents where fieldName is either null or does not exist.

beginner

How do you query documents where a Boolean field is true?

Use { fieldName: true } in your query to find documents where fieldName is exactly true.

intermediate

What is the difference between a field set to null and a field that does not exist in MongoDB?

A field set to null exists in the document but has no value. A field that does not exist is completely missing from the document. Queries for { field: null } match both cases.

Which of the following is a valid Boolean value in MongoDB?

A true

B "true"

C 1

D yes

MongoDB Boolean values are strictly true or false without quotes.

What does a null value mean in a MongoDB document?

A The field exists but has no value

B The field is missing

C The field is set to false

D The field is set to zero

null means the field exists but has no assigned value.

How do you find documents where a Boolean field is false?

A { fieldName: 0 }

B { fieldName: null }

C { fieldName: false }

D { fieldName: 'false' }

Use the Boolean value false without quotes to query Boolean false.

Which query matches documents where a field is either null or missing?

A { fieldName: '' }

B { fieldName: false }

C { fieldName: undefined }

D { fieldName: null }

Querying with null matches both null values and missing fields.

If a field is missing in a document, what will a query { fieldName: true } return?

A Documents where fieldName is false

B Documents where fieldName is true

C Documents where fieldName is null

D Documents where fieldName is missing

The query matches only documents where the field exists and is true.

Explain how Boolean and null types are used in MongoDB documents and how to query them.

Think about yes/no values and empty or missing fields.

Describe the difference between a field set to null and a field that does not exist in MongoDB.

Consider presence versus absence of the field.