Here is a simple example of a database schema migration where:
- a column is added to an existing table
- a table is added
// Our database path
String path;
// Our database once opened
Database db;In the examples below, factory can be replaced by sqfliteDatabaseFactory when using sqflite.
The first version creates a Company table with a name column.
/// Create tables
void _createTableCompanyV1(Batch batch) {
batch.execute('DROP TABLE IF EXISTS Company');
batch.execute('''CREATE TABLE Company (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT
)''');
}
// First version of the database
db = await factory.openDatabase(path,
options: OpenDatabaseOptions(
version: 1,
onCreate: (db, version) async {
var batch = db.batch();
_createTableCompanyV1(batch);
await batch.commit();
},
onDowngrade: onDatabaseDowngradeDelete));
Let say we want to add a new table Employee with a reference to a Company entity.
We also want to add a new column description in the Company entity.
We handle the creation of a fresh database in onCreate and handle the schema migration in onUpgrade. Also since we
want to use foreign key constraints, we configure our access in onConfigure.
/// Let's use FOREIGN KEY constraints
Future onConfigure(Database db) async {
await db.execute('PRAGMA foreign_keys = ON');
}
/// Create Company table V2
void _createTableCompanyV2(Batch batch) {
batch.execute('DROP TABLE IF EXISTS Company');
batch.execute('''CREATE TABLE Company (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT,
description TEXT
)''');
}
/// Update Company table V1 to V2
void _updateTableCompanyV1toV2(Batch batch) {
batch.execute('ALTER TABLE Company ADD description TEXT');
}
/// Create Employee table V2
void _createTableEmployeeV2(Batch batch) {
batch.execute('DROP TABLE IF EXISTS Employee');
batch.execute('''CREATE TABLE Employee (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT,
companyId INTEGER,
FOREIGN KEY (companyId) REFERENCES Company(id) ON DELETE CASCADE
)''');
}
// 2nd version of the database
db = await factory.openDatabase(path,
options: OpenDatabaseOptions(
version: 2,
onConfigure: onConfigure,
onCreate: (db, version) async {
var batch = db.batch();
// We create all the tables
_createTableCompanyV2(batch);
_createTableEmployeeV2(batch);
await batch.commit();
},
onUpgrade: (db, oldVersion, newVersion) async {
var batch = db.batch();
if (oldVersion == 1) {
// We update existing table and create the new tables
_updateTableCompanyV1toV2(batch);
_createTableEmployeeV2(batch);
}
await batch.commit();
},
onDowngrade: onDatabaseDowngradeDelete));
You will have to restart your app when you change your application schema. Flutter Hot-reload won't work unless you properly close currently opened databases.