Migrations support

A simple migrations mechanism. Leverage the existing querying features to do migrations also.

So to define a migration:

[Migration(20190127135100, "A sample migration")]
public class SampleMigration : Migration
{
    public override void Up()
    {
        // Some queries here
    }

    public override void Down()
    {
        // Some queries here
    }
}

And to start a migration flow:

var migrationController = new MigrationController();

migrationController.LoadMigrationsFromAssembly(this.GetType().Assembly);

migrationController.VersionQueryHandler = () =>
{
    try
    {
        var version = Query.New<SchemaGlobals>()
            .Select(SchemaGlobals.Columns.Data)
            .Where(SchemaGlobals.Columns.Key, "version")
            .LimitRows(1)
            .ExecuteScalar() as string;
        if (version == null) return 0;
        return Convert.ToInt64(version);
    }
    catch
    {
        Query.New<SchemaGlobals>().CreateTable().Execute();
        return 0;
    }
};

migrationController.MigrationVersionEvent += (sender, args) =>
{
    Query.New<SchemaGlobals>()
        .Insert(SchemaGlobals.Columns.Key, "version")
        .Insert(SchemaGlobals.Columns.Data, args.Version)
        .InsertOrUpdate()
        .Execute();
};

migrationController.ItemStartEvent += (sender, args) =>
{
    logger.Info($"Migrating db to version {args.Version}: {args.Description ?? args.Type.Name}...");
};

migrationController.ItemEndEvent += (sender, args) =>
{
    logger.Info($"Migrating db to version {args.Version}: {args.Description ?? args.Type.Name} - Done.");
};

try
{
    var count = migrationController.MigrateUp();

    if (count > 0)
    {
        logger.Info($"Successfully ran {count} migrations.");
    }
}
catch (Exception ex)
{
    logger.Error(ex, "Migration failed.");

    try
    {
        migrationController.Rollback();
    }
    catch (Exception rex)
    {
        logger.Error(rex, "Migration rollback failed.");
    }
}