👐 Add last three reviews to each book (from reviews table)

We want to modify the MongoDB schema so that each book contains an array of its latest three reviews.

info

This is an implementation of the Subset Pattern.

In this step we will embed the book details into the empty array from the join table.

• On the MongoDB diagram view, click the books collection
• On the relational mappings list on the right, click + Add
• Select Embedded array
• Select reviews as Source table
• In the advanced settings, check Add array conditions
• In Sort by and order option, select timestamp and toggle the order to descending
• Set Limit number of rows to 3
• Uncheck the bookId and leave the rest of the fields checked
• Click Save and close

Limitations:

• Continuous Migration Mode will not support this transformation
• You will not be able to enable Data Verification when you create the Migration Job.