Question

A blog platform stores each Post document and separate Comment documents, all partitioned by postId in the same container. Product wants each Post to display a commentCount without running an aggregate query on every page load. You need the commentCount on the Post to stay accurate whenever a comment is inserted, and the update must occur within the same logical operation. Which approach best satisfies this requirement?

Accepted Answer

Attach a post-trigger to the comment insert operation that reads the parent Post and increments its commentCount, since both documents share the postId partition key.

Answer

Attach a pre-trigger to the comment insert that queries all comments for the post and recalculates commentCount before the insert completes.

Answer

Create a UDF that computes commentCount at query time so the Post document never needs to store the value.

Answer

Use a change feed processor to asynchronously recompute and patch commentCount on the Post after comments are written.