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.profiles.updateOne({ _id: 1 }, { $set: { "contacts.$[elem].value": "new@x.com" } }, { arrayFilters: [{ "elem.type": "email" }] })

  Why this is correct

  The positional filtered operator $[elem] combined with arrayFilters updates only array elements matching the filter, so just the email subdocument's value changes. This is the precise tool when an array contains mixed element types and only some should be modified. It avoids touching phone or other entries.

• ✗

  db.profiles.updateOne({ _id: 1 }, { $set: { "contacts.$.value": "new@x.com" } })

  Why it's wrong here

  The positional $ operator refers to the first array element matched by the query filter, but the query here filters only on _id, so no array element was matched. Without a filter on the array, the positional operator cannot identify the email subdocument and the update fails or targets incorrectly. It requires a matching condition in the query itself.

• ✗

  db.profiles.updateOne({ _id: 1 }, { $set: { contacts: [{ type: "email", value: "new@x.com" }] } })

  Why it's wrong here

  This replaces the entire contacts array with a single-element array, destroying all other contact entries. It is a wholesale overwrite rather than a targeted element update. While the email value would change, the collateral loss of other contacts makes it incorrect for the stated requirement of leaving other elements untouched.

• ✗

  db.profiles.updateOne({ _id: 1 }, { $set: { "contacts.0.value": "new@x.com" } })

  Why it's wrong here

  Using the numeric index 0 targets whatever subdocument happens to be first, which may not be the email entry. Array order is not guaranteed to match semantic type, so this risks overwriting the wrong contact. It does not satisfy the requirement to update specifically the element whose type is email.