Migration
public abstract class Migration
Base class for a database migration.
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 |
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final int |
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final int |
Public constructors |
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Migration(int startVersion, int endVersion)Creates a new migration between |
Public methods |
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abstract void |
migrate(@NonNull SupportSQLiteDatabase database)Should run the necessary migrations. |
Public fields
Public constructors
Migration
public Migration(int startVersion, int endVersion)
Creates a new migration between startVersion and endVersion.
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int startVersion |
The start version of the database. |
int endVersion |
The end version of the database after this migration is applied. |
Public methods
migrate
public abstract void migrate(@NonNull SupportSQLiteDatabase database)
Should run the necessary migrations.
This 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.
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@NonNull SupportSQLiteDatabase database |
The database instance |