InvalidationTracker

public final class InvalidationTracker

The invalidation tracker keeps track of tables modified by queries and notifies its created Flows about such modifications.

A Flow tracking one or more tables can be created via createFlow. Once the Flow stream starts being collected, if a database operation changes one of the tables that the Flow was created from, then such table is considered 'invalidated' and the Flow will emit a new value.

Summary

Public methods
final @NonNull Flow<@NonNull Set<@NonNull String>>
createFlow(@NonNull String tables, boolean emitInitialState)

Creates a Flow that tracks modifications in the database and emits sets of the tables that were invalidated.
final void

Refresh created Flows asynchronously, emitting new values on those whose tables have been invalidated.

Public methods

createFlow

public final @NonNull Flow<@NonNull Set<@NonNull String>> createFlow(@NonNull String tables, boolean emitInitialState)

Creates a Flow that tracks modifications in the database and emits sets of the tables that were invalidated.

The Flow will emit at least one value, a set of all the tables registered for observation to kick-start the stream unless emitInitialState is set to false.

If one of the tables to observe does not exist in the database, this functions throws an IllegalArgumentException.

The returned Flow can be used to create a stream that reacts to changes in the database:

fun getArtistTours(from: Date, to: Date): Flow<Map<Artist, TourState>> {
  return db.invalidationTracker.createFlow("Artist").map { _ ->
    val artists = artistsDao.getAllArtists()
    val tours = tourService.fetchStates(artists.map { it.id })
    associateTours(artists, tours, from, to)
  }
}
Parameters
@NonNull String tables

The name of the tables or views to track.
boolean emitInitialState

Set to false if no initial emission is desired. Default value is true.

refreshAsync

Added in 2.7.0-alpha08
public final void refreshAsync()

Refresh created Flows asynchronously, emitting new values on those whose tables have been invalidated.

This function should be called after any write operation is performed on the database, such that tracked tables and its associated flows are notified if invalidated. In most cases Room will call this function automatically but if a write operation is performed on the database via another connection or through RoomDatabase.useConnection you might need to invoke this function manually to trigger invalidation.