Flow를 반환하는 반응형 조회

A one-time query gives you data once, but the table keeps changing. You want the UI to refresh whenever rows are added or removed.

Change a DAO query to return a Flow. Room now emits a fresh list every single time the underlying table changes. 🔄

A Flow query is not marked suspend. It returns the stream immediately, and emissions arrive as the data updates over time.

Behind the scenes Room tracks which tables a query touches. When any of them changes, it re-runs the query and emits a new value.

In your ViewModel, collect the Flow inside a coroutine. Use viewModelScope so collection stops when the ViewModel clears.

Convert the stream into observable UI state with stateIn, giving an initial value so the screen has something to show at once.

In the Composable read the StateFlow with collectAsStateWithLifecycle. The list recomposes automatically on every change.

Insert a row anywhere and the Flow emits again, so the new item shows up instantly without you refreshing manually.

You can transform results with map before they reach the UI, like sorting or filtering, all reactively in the stream.

Flow integrates cleanly with coroutines and Compose, making it the modern choice over LiveData for reactive Room queries.

With reactive queries the database becomes your single source of truth, and the UI is just a reflection of it at every moment.

What happens when a Room DAO query returns a Flow?

You made queries return Flow, collected them into state, and watched Compose redraw on every change. Next you will organize this behind a repository.