Umbraco Migrations example

CustomMigrationEventHandler

public class CustomMigrationEventHandler : ApplicationEventHandler
{
    protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
    {
        // check target version
        var rawTargetVersion = ConfigurationManager.AppSettings["app:MigrationVersion"] ?? "1.0.0";
        var targetVersion = SemVersion.Parse(rawTargetVersion);
        if (targetVersion != null)
        {
            HandleMigrations(targetVersion);
        }

        base.ApplicationStarted(umbracoApplication, applicationContext);
    }

    private void HandleMigrations(SemVersion targetVersion)
    {
        // get all migrations already executed
        var currentVersion = new SemVersion(0, 0, 0);
        var migrations = ApplicationContext.Current.Services.MigrationEntryService.GetAll(MigrationNames.MyCustomNamespace);

        // get the latest migration executed
        var latestMigration = migrations.OrderByDescending(x => x.Version).FirstOrDefault();
        if (latestMigration != null)
        {
            currentVersion = latestMigration.Version;
        }

        if (targetVersion == currentVersion)
        {
            // nothing to do
            return;
        }

        var migrationsRunner = new MigrationRunner(
            ApplicationContext.Current.Services.MigrationEntryService,
            ApplicationContext.Current.ProfilingLogger.Logger,
            currentVersion,
            targetVersion,
            MigrationNames.MyCustomNamespace);

        try
        {
            // run migrations
            migrationsRunner.Execute(UmbracoContext.Current.Application.DatabaseContext.Database);
        }
        catch (Exception e)
        {
            LogHelper.Error<MigrationEvents>("Error running migration", e);
        }
    }
}

MyCustomTableMigration

/// <summary>
/// MyCustomTable migration
/// </summary>
[Migration("1.0.0", 1, MigrationNames.MyCustomNamespace)]
public class MyCustomTableMigration : MigrationBase
{
    private const string TableName = "MyCustomTable";

    public MyCustomTableMigration(ISqlSyntaxProvider sqlSyntax, ILogger logger)
        : base(sqlSyntax, logger)
    {            
    }

    /// <summary>
    /// Process database upgrade
    /// </summary>
    public override void Up()
    {            
        // create a new table if it doesn't exist
        var tables = SqlSyntax.GetTablesInSchema(Context.Database).ToList();
        if (!tables.InvariantContains(TableName))
        {
            Create.Table(TableName);
        }

        // or you can run alterations on existing tables
        var columns = SqlSyntax.GetColumnsInSchema(Context.Database).ToArray();
        var columnExists = columns.Any(x =>
            string.Equals(x.TableName, tableName) &&
            string.Equals(x.ColumnName, columnName)
        );
        if (!columnExists)
        {
            Alter.Table("SomeOtherTable").AddColumn("MyCustomString").AsString().Nullable();
        }
    }

    /// <summary>
    /// Process database downgrade
    /// </summary>
    public override void Down()
    {
        // drop the table
        Delete.Table(TableName);

        // remove the column from existing table
        Delete.Column("MyCustomString").FromTable("SomeOtherTable");
    }
}