How it works...

In this recipe, we implement a listener function that consumes upstream events and populates a materialized view that is used by a Backend For Frontend service. This function is a stream processor, such as the one we discussed in the Creating a stream processor recipe in Chapter 1, Getting Started with Cloud-Native. The function performs a filter for the desired events and then transforms the data in a map step to the desired materialized view. The materialized view is optimized to support the requirements of the query needed by the BFF. Only the minimum necessary data is stored, and the optimal database type is used. In this recipe, the database type is Elasticsearch. Elasticsearch is a good choice for a materialized view when the data must be searched and filtered. Note that the asOf timestamp is included in the record so that the user can access the latency of the data.