$size operator for array length in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find documents where the array 'tags' has exactly 3 elements.

MongoDB

{ tags: { $[1]: 3 } }

Drag options to blanks, or click blank then click option'

AlengthOf

Blength

Ccount

D$size

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length' or 'count' instead of '$size' causes errors.

Omitting the dollar sign before 'size'.

The $size operator matches arrays with the specified number of elements.

2fill in blank

medium

Complete the aggregation pipeline stage to add a field 'tagCount' with the length of the 'tags' array.

MongoDB

{ $addFields: { tagCount: { $[1]: "$tags" } } }

Drag options to blanks, or click blank then click option'

Alength

B$size

ClengthOf

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using operators like $length or $count which do not exist in MongoDB aggregation.

Forgetting to use quotes around the field name.

The $size operator returns the number of elements in an array field.

3fill in blank

hard

Fix the error in the query to find documents where 'items' array length is 5.

MongoDB

{ items: { $[1]: 5 } }

Drag options to blanks, or click blank then click option'

A$size

Blength

Ccount

DlengthOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using $length or $count which are invalid operators.

Missing the dollar sign before 'size'.

The correct operator to check array length in MongoDB queries is $size.

4fill in blank

hard

Fill both blanks to create a match stage that filters documents where 'comments' array length is greater than 2.

MongoDB

{ $match: { comments: { $[1]: { $[2]: 2 } } } }

Drag options to blanks, or click blank then click option'

A$size

B$gt

C$lt

D$eq

Attempts:

3 left

💡 Hint

Common Mistakes

Using $lt instead of $gt for greater than comparison.

Using $eq which checks equality, not greater than.

Use $size to check array length and $gt to compare if length is greater than 2.

5fill in blank

hard

Fill both blanks to create an aggregation stage that filters documents with 'reviews' array length equal to 4 and adds a field 'reviewCount' with that length.

MongoDB

{ $match: { reviews: { $[1]: 4 } } }, { $addFields: { reviewCount: { $[2]: "$reviews" } } }

Drag options to blanks, or click blank then click option'

A$size

Ccount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count' which is not a valid operator.

Using '$size' as a string in $match which expects operator without quotes.

Use $size in both $match and $addFields stages to check and assign array length.