$or operator behavior in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $or operator do in MongoDB queries?

The $or operator allows you to specify multiple conditions, and it returns documents that satisfy at least one of those conditions.

beginner

How do you structure a query using $or in MongoDB?

You use $or with an array of condition objects. For example: { $or: [ { age: { $lt: 30 } }, { city: 'New York' } ] } finds documents where age is less than 30 OR city is New York.

intermediate

If a document matches multiple conditions inside $or, how many times does it appear in the result?

The document appears only once in the result, even if it matches multiple $or conditions.

intermediate

Can $or be combined with other operators in the same query?

Yes, $or can be combined with other operators like $and, $not, or direct field queries to build complex filters.

advanced

What happens if you use $or with an empty array in MongoDB?

Using $or with an empty array returns no documents because there are no conditions to satisfy.

What does the MongoDB $or operator require as its value?

A An array of condition objects

B A single condition object

C A string value

D A number

The $or operator requires an array of condition objects to check if any condition is true.

If a document matches two conditions inside $or, how many times will it appear in the query result?

A Never

B Twice

C Depends on the query

D Once

Documents appear only once in the result even if they match multiple $or conditions.

Which of the following is a valid $or query in MongoDB?

A { $or: 'age > 20' }

B { $or: [ { age: { $gt: 20 } }, { city: 'Paris' } ] }

C { $or: { age: 20, city: 'Paris' } }

D { $or: 20 }

The $or operator must have an array of condition objects as its value.

What will happen if you run a query with $or: []?

A Returns documents matching the first condition

B Returns all documents

C Returns no documents

D Throws an error

An empty array means no conditions to satisfy, so no documents are returned.

Can $or be used together with $and in the same MongoDB query?

A Yes, to combine multiple logical conditions

B No, they cannot be combined

C Only if <code>$and</code> is inside <code>$or</code>

D Only if <code>$or</code> is inside <code>$and</code>

You can combine $or and $and to create complex queries.

Explain how the $or operator works in MongoDB queries and give an example.

Think about how you would find documents that meet one or more criteria.

Describe what happens if a document matches multiple conditions inside a $or operator.

Consider how query results avoid repetition.