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.reviews.find({}, { author: true, rating: true })

  Why it's wrong here

  This projection includes author and rating but leaves _id in the results, because _id is returned by default unless explicitly excluded. The developer asked for the _id field to be omitted, so this query returns more data than requested even though the field selection is otherwise correct.

• ✗

  db.reviews.aggregate([{ $project: { author: 0, rating: 0, _id: 0 } }])

  Why it's wrong here

  A $project stage with values of 0 is an exclusion projection, so this pipeline removes author and rating while keeping every other field, the reverse of what was requested. It also returns a cursor from aggregate rather than the simple find result the developer expected.

• ✗

  db.reviews.find({ author: 1, rating: 1, _id: 0 })

  Why it's wrong here

  Here the field document is passed as the query filter, not the projection, so MongoDB interprets it as a match condition. It would look for documents whose author equals 1 and rating equals 1, returning almost nothing instead of projecting fields, which is the opposite of the intended behavior.

• ✓

  db.reviews.find({}, { author: 1, rating: 1, _id: 0 })

  Why this is correct

  The second argument of find is the projection document. Setting author and rating to 1 includes only those fields, and _id: 0 explicitly suppresses the default inclusion of _id, producing exactly the reduced payload the developer wants.