Custom event hooks

there are currently two hooks for tapping into. OnBeforeSave and OnBeforeUpdate so that you can perform modifications to the operation that's about to happen. it can also be used as an alternative to the pre-baked audit fields functionality for more fine-grain control. make sure to override both methods in order to cover all the bases.

say for example, you have a Flower entity like the following and you want to automatically set the creator/date when new flowers are being persisted and also modify the updater/date when existing entities get updated.

public class Flower : Entity
{
    public string Name { get; set; }

    public string CreatedBy { get; set; }
    public DateTime CreatedDate { get; set; }

    public string UpdatedBy { get; set; }
    public DateTime UpdateDate { get; set; }
}

to be able to tap in to the hooks, create a derived DBContext class and override the two methods as follows:

public class MyDBContext : DBContext
{
    protected override Action<T> OnBeforeSave<T>()
    {
        Action<Flower> action = f =>
        {
            if (f.ID == null)
            {
                f.CreatedBy = "God";
                f.CreatedDate = DateTime.MinValue;
            }
            else
            {
                f.UpdatedBy = "Human";
                f.UpdateDate = DateTime.UtcNow;
            }
        };
        return action as Action<T>;
    }

    protected override Action<UpdateBase<T>> OnBeforeUpdate<T>()
    {
        Action<UpdateBase<Flower>> action = update =>
        {
            update.AddModification(f => f.UpdatedBy, "Human");
            update.AddModification(f => f.UpdateDate, DateTime.UtcNow);
        };
        return action as Action<UpdateBase<T>>;
    }
}

after that, simply create new instances of MyDBContext when you need the above functionality and perform operations as usual like so:

var db = new MyDBContext();

await db.SaveAsync(new Flower() { Name = "Red Rose" });

await db.Update<Flower>()
        .Match(f => f.Name == "Red Rose")
        .Modify(f => f.Name, "White Rose")
        .ExecuteAsync();

Handling multiple entity types

it's possible to handle more than one type of entity inside the hooks like below:

protected override Action<T> OnBeforeSave<T>()
{
    var type = typeof(T);

    if (type == typeof(Book))
    {
        Action<Book> action = b =>
        {
            b.SavedBy = "Author";
            b.SavedOn = DateTime.UtcNow;
        };
        return action as Action<T>;
    }

    if (type == typeof(Flower))
    {
        Action<Flower> action = f =>
        {
            f.SavedBy = "Human";
            f.SavedOn = DateTime.MinValue;
        };
        return action as Action<T>;
    }

    return null;
}