C100DEV CRUD Operations 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.

• ✓

  db.shipments.updateMany({}, { $pull: { events: { status: 'cancelled' } } })

  Why this is correct

  The $pull operator removes all array elements that match a specified condition. Here, it removes subdocuments where status equals 'cancelled' from the 'events' array in every document. It does not affect other array elements, and updateMany applies the change to all matching documents. This is the correct tool for removing specific array elements based on a field value.

• ✗

  db.shipments.updateMany({}, { $pullAll: { events: [{ status: 'cancelled' }] } })

  Why it's wrong here

  $pullAll removes all instances of the specified values from an array. It requires exact matches of entire elements, not partial matches on subdocument fields. Since the subdocuments also contain a 'timestamp' field, an exact match with only 'status' would not match any elements. Thus, it would not remove the intended subdocuments.

• ✗

  db.shipments.updateMany({}, { $unset: { events: { status: 'cancelled' } } })

  Why it's wrong here

  $unset removes a field entirely, not an array element. Using it with a query on an array element is not valid syntax for removing a subdocument from an array. It would either fail or remove the entire 'events' field if used with a positional operator, which is not the intended behavior. It does not selectively remove matching array elements.

• ✗

  db.shipments.updateMany({}, { $pop: { events: { status: 'cancelled' } } })

  Why it's wrong here

  $pop removes the first or last element of an array, not elements matching a condition. It takes a value of 1 or -1 to indicate which end to remove. It cannot filter by subdocument fields. Using it here would remove an arbitrary element from the array, not necessarily the one with status 'cancelled', leading to data corruption.