C100DEV Aggregation Framework Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  $elemMatch

  Why it's wrong here

  $elemMatch is used to match documents that contain at least one element that satisfies all criteria in a sub-document. It focuses on finding specific objects within an array, whereas $all is used to check for the presence of multiple individual values within an array.

• ✗

  $in

  Why it's wrong here

  $in matches any document where the field value equals any value in the provided list. If applied to an array, it returns true if any single element of the document's array matches any element in the query list, failing the requirement of containing ALL elements.

• ✓

  $all

  Why this is correct

  $all requires that the specified array field contains all elements specified in the query array, regardless of order. This is the correct operator for ensuring that a collection of mandatory tags or values is present, which is common in content management and inventory applications.

• ✗

  $size

  Why it's wrong here

  $size restricts the search to arrays of a specific length. While useful for checking the quantity of elements, it does not evaluate the content of the elements themselves, making it insufficient for ensuring that specific mandatory items are included within the array field.