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.

• ✗

  $add

  Why it's wrong here

  $add is an aggregation framework expression used within $project or $group stages, not an update operator. Attempting to use it in an update document will result in an error, as update operations require specific modifiers like $inc to change document data outside of an aggregation pipeline.

• ✓

  $inc

  Why this is correct

  The $inc operator atomically increments a field by the specified amount. It supports both positive and negative values for incrementing and decrementing, respectively. This is the correct choice for managing counters, such as page views or inventory levels, where accuracy under high concurrency is a strict requirement.

• ✗

  $set

  Why it's wrong here

  $set overwrites the existing value with a new value. To use $set for incrementing, you would need to fetch the value first, update it in your code, and send it back. This sequence is not atomic and risks overwriting changes made by other concurrent database operations.

• ✗

  $mul

  Why it's wrong here

  $mul is used for multiplying the value of a field by the specified number. While it is a numeric update operator, it performs multiplication rather than addition. It is useful for scaling values, but it does not accomplish the task of incrementing a field by a specific amount.