Simple.Migrations

To support a new database engine, you must implement IDatabaseProvider<TConnection>. The implementation strategy depends on whether you want to support concurrent migrators:

1. No Concurrency Support

Subclass DatabaseProviderBaseWithAdvisoryLock. Override AcquireAdvisoryLock() and ReleaseAdvisoryLock() to do nothing. Implement the SQL methods: GetcreateVersionTableSql(), GetCurrentVersionSql(), and GetSetVersionSql().

2. Concurrency via Advisory Locks

Subclass DatabaseProviderBaseWithAdvisoryLock. Implement AcquireAdvisoryLock() and ReleaseAdvisoryLock() using your database's specific advisory lock mechanism. Implement the SQL methods: GetcreateVersionTableSql(), GetCurrentVersionSql(), and GetSetVersionSql().

3. Concurrency via Version Table Locking

Subclass DatabaseProviderBaseWithVersionTableLock. Implement AcquireVersionTableLock() by creating a transaction on this.VersionTableConnection and executing SQL to lock the table. Implement ReleaseVersionTableLock() by destroying the transaction. Implement the SQL methods: GetcreateVersionTableSql(), GetCurrentVersionSql(), and GetSetVersionSql().

The SimpleMigrator class is the primary entry point for managing migrations. It handles finding migrations in an assembly and executing them against a database.

Important: You must call .Load() before calling any other methods on the migrator instance.

Key Methods:

• Load(): Discovers migrations in the provided assembly and queries the database for the current version.
• MigrateTo(n): Migrates the database to a specific version n. Use MigrateTo(0) to remove all migrations.
• MigrateToLatest(): A shortcut to migrate to the most recent version found in the assembly.
• Baseline(n): Updates the version table to version n without actually running any migration classes. Useful for existing databases.
• CurrentMigration: Property returning the current version of the schema.
• Migrations: Property returning an ordered list of all discovered migrations.

var migrationsAssembly = typeof(Program).Assembly;
using (var db = new SQLiteConnection("DataSource=database.sqlite"))
{
    var databaseProvider = new SqliteDatabaseProvider(db);
    var migrator = new SimpleMigrator(migrationsAssembly, databaseProvider);

    migrator.Load();
    migrator.MigrateToLatest();
}

Migrations are classes that derive from Migration (for ADO.NET) or implement IMigration<TConnection>. They must be decorated with the [Migration(versionNumber)] attribute.

Key features:

• Up(): Overridden method to apply changes. Invoked when migrating up.
• Down(): Overridden method to revert changes. Invoked when migrating down.
• Execute(string sql): Inherited method to execute raw SQL. It automatically logs the SQL via the Logger.
• UseTransaction: A boolean property (default true) that determines if the migration runs inside a transaction. Set to false if your database engine requires non-transactional SQL for certain operations.

using SimpleMigrations;

namespace Migrations
{
    [Migration(1, "Create Users table")]
    public class CreateUsers : Migration
    {
        protected override void Up()
        {
            Execute(@"CREATE TABLE Users (
                Id SERIAL NOT NULL PRIMARY KEY,
                Name TEXT NOT NULL
            )");
        }

        protected override void Down()
        {
            Execute("DROP TABLE Users");
        }
    }
}