Support value generation with converters

[ajcvickers]

Current behavior is to throw by default if a converter is associated with a property that will use value generation
However, a value generator to use can be specified:

• On the property
• On the type mapping
• On a converter

A client-side generator is added to the Guid converters so that Guid key scenarios still work. We should find similar "safe" cases and make those work as well.

Original PR: #11479

[ajcvickers]

Consider the Oracle case in #11559 when looking into this.

[ajcvickers]

Note: when working on this, also consider #11970

[twsl]

Is anyone already working on this and is there an ETA? If not, would you accept PR's for this?

[ajcvickers]

@twsI It's in the 3.0 milestone, which means it is tentatively planned for 3.0. I don't believe anyone is working on it right now. We would consider PRs, but it would be helpful if you could provide some details of what you plan to do before submitting a PR, since it's not clear what the behavior here should be or how it should be implemented.

[lars-lindstrom]

Have anyone got this to work on a strongly typed Id using Guids? I can get it to work on Integer types, but not using Guids in the record struct.

public readonly record struct StronglyTypedGuidId
{
    public StronglyTypedGuidId(Guid id)
    {
        Value = id;
    }

    public Guid Value { get; }

    public static StronglyTypedGuidId Create(Guid entityId) => new(entityId);
}

public readonly record struct StronglyTypedIntId
{
    public StronglyTypedIntId(intid)
    {
        Value = id;
    }

    public int Value { get; }

    public static StronglyTypedIntId Create(int entityId) => new(entityId);
}

protected override void OnModelCreating(ModelBuilder builder)
{
     base.OnModelCreating(builder);
     builder.Entity<StronglyTypedIntEntity>().Property(entity=>entity.Id).HasConversion<StronglyTypedIntIdValueConverter>().UseIdentityColumn();
     builder.Entity<StronglyTypedGuidEntity>().Property(entity => entity.Id).HasConversion<StronglyTypedGuidIdValueConverter>().UseIdentityColumn();
}

If I apply both the following errors is produced when building the migration:

If I apply both the following errors is produced when building the migration:
Unable to create a 'DbContext' of type ''. The exception 'Identity value generation cannot be used for the property 'Id' on entity type 'StronglyTypedGuidEntity' because the property type is 'StronglyTypedGuidId'. Identity value generation can only be used with signed integer properties.' was thrown while attempting to create an instance. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

If I comment out the Guid version, the migration builds and the following is produced:

migrationBuilder.AlterColumn<int>(
    name: "Id",
    schema: "dbo",
    table: "StronglyTypedIntIdEntities",
    type: "int",
    nullable: false,
    oldClrType: typeof(int),
    oldType: "int")
    .Annotation("SqlServer:Identity", "1, 1");

[ilmax]

I think you shouldn't use .Useidentity with a guid. Also where do you expect the guid to be generated? Db or from the application?

[lars-lindstrom]

I can be I misunderstand the documentation, but it says Guids can be auto generated by the provider. If this happens on the client (by the provider) or in the Db, doesn't make a difference to me.

Primary keys
By convention, non-composite primary keys of type short, int, long, or Guid are set up to have values generated for inserted entities if a value isn't provided by the application. Your database provider typically takes care of the necessary configuration; for example, a numeric primary key in SQL Server is automatically set up to be an IDENTITY column.

https://learn.microsoft.com/da-dk/ef/core/modeling/generated-properties?tabs=data-annotations#explicitly-configuring-value-generation

[ajcvickers]

@lars-lindstrom You need to use ValueGeneratedOnAdd to let EF know that value of this type should be generated. For example:

modelBuilder
    .Entity<Blog>()
    .Property(entity => entity.Id)
    .ValueGeneratedOnAdd()
    .HasConversion<StronglyTypedGuidIdValueConverter>();

Runnable:

using (var context = new SomeDbContext())
{
    await context.Database.EnsureDeletedAsync();
    await context.Database.EnsureCreatedAsync();

    context.Add(new Blog { Name = "X" });
    context.SaveChanges();
}

using (var context = new SomeDbContext())
{
    var blogs = context.Blogs.ToList();
}

public class SomeDbContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(@"Data Source=(LocalDb)\MSSQLLocalDB;Database=AllTogetherNow")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    public DbSet<Blog> Blogs => Set<Blog>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder
            .Entity<Blog>()
            .Property(entity => entity.Id)
            .ValueGeneratedOnAdd()
            .HasConversion<StronglyTypedGuidIdValueConverter>();
    }
}

public class StronglyTypedGuidIdValueConverter : ValueConverter<StronglyTypedGuidId, Guid>
{
    public StronglyTypedGuidIdValueConverter()
        : base(v => v.Value, v => new StronglyTypedGuidId(v))
    {
    }
}

public readonly record struct StronglyTypedGuidId
{
    public StronglyTypedGuidId(Guid id)
    {
        Value = id;
    }

    public Guid Value { get; }

    public static StronglyTypedGuidId Create(Guid entityId) => new(entityId);
}

public class Blog
{
    public StronglyTypedGuidId Id { get; set; }
    public string? Name { get; set; }
}

[lars-lindstrom]

@ajcvickers Thx.
I believe what confused me, was the fact of no ValueGeneratedOnAdd was pressent in the migration files. After your post I found it in the modelsnapshot. With the risk of being completely mistanken, I suspect autogenerated Guids are not created in the DB, but client side by EF Core. Correct, or am I completely wrong? :-)

Any way, huge thank you. And great job you and rest the team are doing on EF Core.

[ajcvickers]

@lars-lindstrom By default they are generated on the client. This can be changed to server generating using .HasDefaultValueSql to specify the database function to use--usually newsequentialid.