How to prevent come code deletion in DbContext while updating model in database first Entity Framework

Question

I have a database-first DbContext and I added some audit related code in the DbContext class, but when I update the model, it deleted my written code in DbContext class. Please tell me how to retain this code even after model update.

Here is my code and I added comments which code is deleting after model update:

public partial class MyDbContext : DbContext
{
    public MyDbContext()
        : base("name=ODbContext")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

    public virtual DbSet<AspNotification> AspNotifications { get; set; }
    public virtual DbSet<ASPAudit> ASPAudit { get; set; }

    // this code is removed whenever I update model
    public override int SaveChanges()
    {
         var addedEntries = ChangeTracker.Entries().Where(e => e.State == EntityState.Added).ToList();
         
        int changes = base.SaveChanges();

        foreach (var entry in addedEntries)
        {
           ...some code
        }

        base.SaveChanges();

        return changes;
    }
}

It would be great if anyone guide me

Answer 1

If you look at top of that generated class, you'll see:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated from a template.
//
//     Manual changes to this file may cause unexpected behavior in your application.
//     Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

That means this class will be auto-generated on every update.

EF generated classes are partial, you can create and add your extensions/changes to other half of partial class (for example MyDbContextPartial.cs).

// file MyDbContextPartial.cs
public partial class MyDbContext
{
    public override int SaveChanges()
    {
         var addedEntries = ChangeTracker.Entries().Where(e => e.State == EntityState.Added).ToList();
         
        int changes = base.SaveChanges();
        foreach (var entry in addedEntries)
        {
           ...some code
        }

        base.SaveChanges();
        return changes;
    }
}