In this module, you handle the final access pattern — find all past games for a user. Users in the application might want to view games they’ve played to watch replays, or they might want to view their friends’ games.
You might recall that there is a many-to-many relationship between the Game entity and the associated User entities, and the relationship is represented by a UserGameMapping entity.
Often, you want to query both sides of a relationship. With the primary key setup, you can find all the User entities in a Game. You can enable querying all Game entities for a User by using an inverted index.
In DynamoDB, an inverted index is a global secondary index (GSI) that is the inverse of your primary key. The sort key becomes your partition key and vice versa. This pattern flips your table and allows you to query on the other side of your many-to-many relationships.
In the following steps, you add an inverted index to the table and see how to use it to retrieve all Game entities for a specific User.