MyMigrationComposer.cs

using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Models;

using uSync.Core;
using uSync.Migrations.Composing;
using uSync.Migrations.Migrators;
using uSync.Migrations.Notifications;

namespace MyMigrations;

/// <summary>
///  this is an example of how you might extend, and replace
///  core migrations for certain types (e.g the grid)
/// </summary>
/// <remarks>
///  by default the core will convert what it can, but if you
///  want to do something special, you can implement your
///  own ISyncPropertyMigrator and remove the core ones.
/// </remarks>

/// **********************************************************
/// NOTE: This project is not referenced in the Sample site
///       so this code isn't going to actually fire.
/// **********************************************************

[ComposeAfter(typeof(SyncMigrationsComposer))]
public class MySyncMigrationComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // if we have a custom migration for the grid, we should 
        // remove the existing one. 
        // builder.SyncPropertyMigrators().Replace<GridMigrator, GridToBlockListMigrator>();

        // our migration will be discovered, if it implements ISyncItemMigrator

        // you can also intercept with notifications
        builder.AddNotificationHandler<SyncMigratedNotification<Content>, MySyncMigratedNotificationHandler>();
    }
}

/// <summary>
///  the migrated handler is fired pre save to disk, so 
///  if you want to do extra work on the xml you could do it here. 
/// </summary>
public class MySyncMigratedNotificationHandler : INotificationHandler<SyncMigratedNotification<Content>>
{
    public void Handle(SyncMigratedNotification<Content> notification)
    {
        // you can also use the usync xml helpers, to quickly get things like the alias or the key.
        var alias = notification.Xml.GetAlias();
        var key = notification.Xml.GetKey();
    }
}