C100DBA 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.

• ✗

  $push

  Why it's wrong here

  The $push operator adds a value to an array regardless of whether the value already exists in that array. This leads to duplicate entries, which may violate data integrity rules in applications that expect unique elements within a tag list or historical event log collection.

• ✗

  $set

  Why it's wrong here

  The $set operator replaces the entire field value. Using $set to add an element would require overwriting the whole array, which is inefficient and risks overwriting concurrent changes made to the array by other application threads, leading to data inconsistency issues in high-concurrency environments.

• ✓

  $addToSet

  Why this is correct

  This operator is specifically designed to treat an array as a mathematical set. It ensures uniqueness by verifying the element's absence before insertion. This atomic behavior is essential for maintaining clean data without the overhead of client-side validation logic or complex multi-step database interactions.

• ✗

  $each

  Why it's wrong here

  The $each operator is a modifier used with $push or $addToSet to add multiple elements. It is not an operator that performs uniqueness checks by itself. It merely iterates over an array of values to be processed by the parent operator assigned to the update.