Query filter syntax in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a query filter in MongoDB?

A query filter is a way to specify conditions to find documents in a collection that match certain criteria.

beginner

How do you filter documents where the field 'age' is exactly 25?

Use { "age": 25 } as the filter to find documents where the 'age' field equals 25.

beginner

What operator do you use to find documents where a field is greater than a value?

Use the $gt operator. For example, { "age": { "$gt": 30 } } finds documents where 'age' is greater than 30.

intermediate

How do you combine multiple conditions in a MongoDB query filter?

By default, listing multiple fields means AND. For OR, use the $or operator with an array of conditions.

intermediate

What does this filter do? { "status": { "$in": ["A", "B"] } }

It finds documents where the 'status' field is either 'A' or 'B'. The $in operator checks if the field matches any value in the array.

Which filter finds documents where 'score' is less than 50?

A { "score": { "$eq": 50 } }

B { "score": { "$gt": 50 } }

C { "score": 50 }

D { "score": { "$lt": 50 } }

The $lt operator means 'less than', so { "score": { "$lt": 50 } } finds scores below 50.

How do you find documents where 'age' is 20 AND 'status' is 'active'?

A { "$or": [ { "age": 20 }, { "status": "active" } ] }

B { "age": 20, "status": "active" }

C { "age": { "$eq": 20 }, "status": { "$eq": "active" } }

D { "$and": [ { "age": 20 }, { "status": "active" } ] }

Listing multiple fields in the filter means AND by default, so option B is correct. Option D is also correct as it explicitly uses $and.

What does the $ne operator do?

A Matches values greater than the specified value

B Matches values equal to the specified value

C Matches values not equal to the specified value

D Matches values less than the specified value

$ne means 'not equal', so it finds documents where the field is not the given value.

Which filter finds documents where 'category' is either 'books' or 'electronics'?

A { "category": { "$in": ["books", "electronics"] } }

B { "category": { "$all": ["books", "electronics"] } }

C { "category": "books" }

D { "$or": [ { "category": "books" }, { "category": "electronics" } ] }

$in matches any value in the array, so option A finds documents with either category. Option D also finds documents with either category using $or.

How do you find documents where 'price' is between 10 and 20 inclusive?

A { "price": { "$gte": 10, "$lte": 20 } }

B { "price": { "$gt": 10, "$lt": 20 } }

C { "price": { "$in": [10, 20] } }

D { "price": { "$ne": 10, "$ne": 20 } }

$gte means 'greater than or equal', $lte means 'less than or equal', so option D finds prices between 10 and 20.

Explain how to write a MongoDB query filter to find documents where a field matches multiple conditions.

Think about combining conditions with AND and OR.

Describe the purpose and usage of the $in operator in MongoDB query filters.

It helps find documents matching any value from a set.