How to Persist Data Annotations in Entity Framework Generated Classes?

Preserving Data Annotations in Entity Framework Generated Code

Question:

How to add data annotations to a class generated by Entity Framework (EF) that persist after code regeneration?

Context:

Consider a class generated by EF:

public partial class ItemRequest
{
    public int RequestId { get; set; }
}

Modifying this code directly to add annotations (e.g., [Required]) will be overwritten on subsequent code generation.

Answer:

EF generates classes as partial classes. Utilizing this, we can create a separate partial class with the desired data annotations:

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;

// Ensure the namespace matches the original class
namespace MvcApplication1.Models
{
    // Metadata class for data annotations
    [MetadataType(typeof(ItemRequestMetaData))]
    public partial class ItemRequest
    {
    }

    public class ItemRequestMetaData
    {
        [Required]
        public int RequestId { get; set; }
    }
}

The MetadataType attribute links the ItemRequestMetaData class to the original ItemRequest class. This allows data annotations in ItemRequestMetaData to be applied to ItemRequest without modifying the generated code.

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