$eq for equality in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $eq operator do in MongoDB?

The $eq operator checks if a field's value is equal to a specified value. It returns documents where the field matches exactly.

beginner

How do you use $eq in a MongoDB query to find documents where age is 30?

You write: { age: { $eq: 30 } }. This finds documents where the age field equals 30.

intermediate

Is { age: 30 } the same as { age: { $eq: 30 } } in MongoDB queries?

Yes, both find documents where age equals 30. The first is shorthand; the second uses $eq explicitly.

intermediate

Can $eq be used to compare fields to null in MongoDB?

Yes, { field: { $eq: null } } finds documents where field is null or does not exist.

beginner

What is the difference between $eq and $ne in MongoDB?

$eq checks for equality (equal to), while $ne checks for inequality (not equal to).

What does { age: { $eq: 25 } } return in MongoDB?

A Documents where age is greater than 25

B Documents where age is not 25

C Documents where age is 25

D Documents where age is less than 25

The $eq operator matches documents where the field equals the specified value.

Is { name: { $eq: "Alice" } } equivalent to { name: "Alice" }?

A Yes, both find documents where name is Alice

B No, they find different documents

C Only the first works

D Only the second works

Both forms find documents where the name field equals "Alice".

Which operator finds documents where a field is NOT equal to a value?

A $eq

B $gt

C $lt

D $ne

$ne means 'not equal', opposite of $eq.

What happens if you query { score: { $eq: null } }?

A Finds documents where score is null or missing

B Finds documents where score is zero

C Finds documents where score is not null

D Returns an error

$eq: null matches fields that are null or do not exist.

Which is a correct way to find documents where status equals "active"?

A { status: "active" }

B Both B and C

C { status: { $eq: "active" } }

D Neither B nor C

Both forms are valid and find documents where status is "active".

Explain how the $eq operator works in MongoDB queries.

Think about how you find items that exactly match a value.

Describe the difference between using $eq and not using it in a MongoDB query.

Consider if <code>{ age: 30 }</code> and <code>{ age: { $eq: 30 } }</code> return the same documents.