MetadataType not working to merge metadata having followed Microsoft tutorial for data first approach

Question

I have tried to simplify this problem as much as possible and cannot find a solution or fix.

I have followed the second approach ("Add metadata class") in this Microsoft tutorial https://learn.microsoft.com/en-us/aspnet/mvc/overview/getting-started/database-first-development/enhancing-data-validation?fbclid=IwAR0_eqraghf-faEqw1d0Fijw9D_su5BGIMMrwQQj4DgYwgiDht5NHLgx3BI

I am using data first with a Razor project. The database scaffolds without problem to create the dbContext. I want to annotate columns eg with Display(Name=""). This cannot go in the scaffolding generated files because they may get overwritten so the tutorial says to create metadata classes in a separate file and then a partial class in another separate file to merge the metadata into the scaffold generated classes. I understand all of this but it doesn't work.

To make it extremely simply I created a table Customer and after running scaffolding I edited the scaffold generated file so that everything was in the one file (so no potential problems with namespace - even though everything was in the same namespace anyway...).

So here is all of the code:

CREATE TABLE [dbo].[Customers] (
      [Id] INT NOT NULL,
      [Name] VARCHAR (30) NOT NULL,
      [Details] VARCHAR (MAX) NOT NULL,
      PRIMARY KEY CLUSTERED ([Id] ASC)
    );

I then edited the Customer.cs class generated by scaffolding to include the metadata class and MetadataType property. The file is:

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
namespace MyProject.Models
{
public partial class Customer
{
public int Id { get; set; }
// [Display(Name ="Customer name")]
// if I put the annotation here it works. If I comment this out and put it in the metadata class it doesn't work
public string Name { get; set; } = null!;
public string Details { get; set; } = null!;
}

[MetadataType(typeof(CustomerMetaData))]
public partial class Customer
{
}

public class CustomerMetaData
{
[Display(Name ="Customer name")]
public string Name";
}
}

So once I've done that I simply created a folder in the Pages folder and right clicked and Add > Razor Page > Razor Pages with EF (CRUD) to generate the default CRUD pages for the Customer class in the dbContext.

So that's it. Nothing complicated. Back in the Customer.cs class file if I put the [Display(Name="Customer Name"] in the Scaffolding generated class it works and the pages display "Customer name" instead of the column name "Name". However, comment out the annotation in the Customer class and put the MetaDataType attribute on a second partial class Customer and have a CustomerMetaData class that includes the annotation and it doesn't work.

I can not get it to work.

The problem is compounded because you cannot see the annotations if you "watch" a data object during debug

Answer 1

I'm experiencing the same issue. I'm in .Net 6, ASP.NET, MVC, with EF Core.

The only way I'm able to get my display name is directly in the view. I can live with that but what's killing me is I can't control the validation stuff that way.

Update:

I somewhat have a hack working. I used a subclass of the model and put the annotations on that. The subclass includes only a copy of the fields I wanted to annotate. I did have to use the [new] keyword but those properties are throw-away anyway. I then adjust the view to use that subclass as the @model.

That's all I changed. I leave the EF context pointing to the original class. The same with all the controllers. The dependency injection gnomes look at what the controller is expecting (the original class) and pipe it in that way.

I'm not 100% happy with this, though. Even though the code impact is the same thing as the metadata class and attribute combo, it's not visibly understandable as to what or why it's doing it. And there is the hidden dependency on dependency injection working correctly.

Update #2:

I changed all of this around to use the data annotation applied to an interface instead. I was able to apply the interface to "user safe" side of the model partial classes, just a stub really, and changed the @model tag on the views to use the interface. I think it's much cleaner and there isn't some hidden context switching between classes.

Answer 2

Found a solution that works using interfaces and Joseph has kindly also confirmed that he's got a solution using interfaces that works (Joseph is your solution the same). For the benefit of anybody reading this in the future here's what I managed to do (let me know if there is a better solution).

scaffolding generated Customer class (which shouldn't be edited to avoid edits being overwritten by subsequent scaffolding) is

namespace project.Models
{
    public partial class Customer
    {
        public int Id { get; set; }
        public string Name { get; set; } = null!;
        public string Info { get; set; } = null!;
    }
}

Created a separate class file in the Models folder called CustomerExtension.cs

namespace project.Models
{
    public partial class Customer : ICustomer
    { }

    public interface ICustomer
    {
        int Id { get; }
        [Display(Name = "Customer name")]
        string Name { get; set; }
        [Display(Name = "Customer info")]
        string Info { get; set; }

    }
}

Then in the Razor or MVC files use ICustomer rather than Customer. The scaffolding tool that can auto generate CRUD pages/views doesn't like using the interface as the model (well at least it didn't for me) so I generated them using Customer and then edited the page/view models to use ICustomer rather that Customer. So in pages such as view changed the model property to:

public ICustomer Customer { get; set; }

This was all I needed to do for simple pages/views that simply display a single record/row such as the Details page and Customer = await _context.Customers.FirstOrDefaultAsync(m => m.Id == id);works. However, for the Index page that displays a list of records/rows the query generated an error. My perhaps crude solution was to cast the data value in a select statement in the query:

Customer = await _context.Customers.Select(e => (ICustomer)e).ToListAsync();

That then works and uses the annotations defined in the interface.