Medium Android App — Migrating from Apollo Kotlin 3 to 4: Lessons Learned

Summary

Migrating the Medium Android app from Apollo Kotlin 3 to 4 exposed cache and exception-handling issues that were hidden by the earlier implementation. Apollo Kotlin 4 uses a new group, plugin, and package identifier, places exceptions in ApolloResponse, and replaces ApolloCompositeException with a primary exception plus suppressed failures. CacheMissException errors appeared in watch() because programmatic cache IDs were incomplete or incorrect; the app addressed this with declarative type and field policies, __typename on every operation, cache-update helpers, and policy-aware safeWatch filtering. The migration also replaced executeV3(), removed fetchThrows = true, added a Currency scalar adapter, and identified HTTP batching and persisted queries as future improvements, while concluding that Apollo 4 produced a more robust cache integration after the underlying issues were fixed.

Takeaways

1. 1

   Declarative type and field policies replaced programmatic cache IDs, making cache keys easier to match to types and fields.

2. 2

   safeWatch filters CacheMissException or ApolloNetworkException according to the selected fetch policy, allowing later fallback responses to reach the UI while preserving meaningful failures.

3. 3

   Apollo Kotlin 4 migration changes included the new com.apollographql.apollo identifier, ApolloResponse-based exception handling, execute() in place of executeV3(), and removal of fetchThrows = true.