Migration

public abstract class Migration


Base class for a database migration.

Creates a new migration between startVersion and endVersion.

Each migration can move between 2 versions that are defined by startVersion and endVersion.

A migration can handle more than 1 version (e.g. if you have a faster path to choose when going version 3 to 5 without going to version 4). If Room opens a database at version 3 and latest version is 5, Room will use the migration object that can migrate from 3 to 5 instead of 3 to 4 and 4 to 5.

If there are not enough migrations provided to move from the current version to the latest version, Room will clear the database and recreate so even if you have no changes between 2 versions, you should still provide a Migration object to the builder.

Summary

Public fields

final int
final int

Public constructors

Migration(int startVersion, int endVersion)

Public methods

abstract void

Should run the necessary migrations.

Public fields

endVersion

Added in 2.0.0
public final int endVersion

startVersion

Added in 2.0.0
public final int startVersion

Public constructors

Migration

Added in 2.0.0
public Migration(int startVersion, int endVersion)

Public methods

migrate

Added in 2.0.0
public abstract void migrate(@NonNull SupportSQLiteDatabase db)

Should run the necessary migrations.

The Migration class cannot access any generated Dao in this method.

This method is already called inside a transaction and that transaction might actually be a composite transaction of all necessary Migrations.

Parameters
@NonNull SupportSQLiteDatabase db

The database instance