C100DEV Data Modeling 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.

• ✗

  Convert the tags array into a comma-separated string.

  Why it's wrong here

  Storing tags as a string forces the engine to perform full-text searches or regex queries, which are significantly slower than multikey index lookups. You lose the ability to perform direct equality matches on specific tags, which negates the indexing benefits provided by MongoDB's native array support.

• ✓

  Use the multikey index created on the tags array.

  Why this is correct

  Multikey indexes are the native way MongoDB handles array indexing. When an index is created on a field that contains an array, MongoDB automatically creates entries for each element, allowing for high-speed retrieval of documents based on specific tag values without any additional configuration or complex data restructuring.

• ✗

  Create one index per tag value to ensure performance.

  Why it's wrong here

  Creating an index for every possible tag value is inefficient and unmanageable as the number of unique tags grows. This would create an enormous number of indexes, consuming excessive memory and slowing down write operations significantly, as every document update would require updating every single tag-specific index.

• ✗

  Store tags in a separate collection and reference them using an object ID.

  Why it's wrong here

  While this is a normalized approach, it is unnecessary for simple tag lookups. The overhead of performing a join or an application-side lookup for every tag query is much higher than simply utilizing a multikey index on the array, which is purpose-built for this exact use case.