At this moment, we have a collection that contains a single object of type ReadModels.UserDetails in memory. This object represents a single user, so we can find out what display name the user has if we have the user ID. This is helpful, but how can we use it to show the full details of our classified ad? There are two ways of doing this, considering that we are within a single-application boundary and use the same store (currently in memory) for all read models.
When developers start to deal with data that is spread across multiple data sources, the most obvious method that comes to their mind is to aggregate data on the edge. One of the most popular techniques is to build BFF. When the frontend needs to get some aggregated data, it sends one request to a single API endpoint at the backend, and the API itself calls different data sources and merges the...