ASP.NET Core MetaDataType Attribute not working

Question

I'm using the MetaDataType Attribute on my domain model class. It it supposed to move the attribute information from the referenced class into the class that the MetadataType attribute has been set. But it doesn't do as advertised. What is causing the issue here?

[MetadataType(typeof(ComponentModelMetaData))] public partial class Component {     public int Id { get; set; }     public string Name { get; set; }     public ICollection<Repo> Repos { get; set; }     public string Description { get; set; }    }   public class ComponentModelMetaData {     [Required(ErrorMessage = "Name is required.")]     [StringLength(30, MinimumLength = 3, ErrorMessage = "Name length should be more than 3 symbols.")]     public string Name { get; set; }     public ICollection<Repo> Repos { get; set; }     [Required(ErrorMessage = "Description is required.")]     public string Description { get; set; }         } 

Answer 1

ASP.NET Core uses

Microsoft.AspNetCore.Mvc **ModelMetadataType**  

instead of

System.ComponentModel.DataAnnotations.**MetadataType**  

source

Try changing your attribute to [ModelMetadataType(typeof(ComponentModelMetaData))]

Answer 2

Entity class:

namespace CoreProject.Persistence.EFCore {     public partial class User     {         public User()         {             Reader = new HashSet<Reader>();             Writer = new HashSet<Writer>();         }          public int UserId { get; set; }         public string Email { get; set; }         public string Password { get; set; }         public string PasswordHashKey { get; set; }         public byte Role { get; set; }         public string FirstName { get; set; }         public string LastName { get; set; }         public DateTime CreatedUtc { get; set; }         public DateTime LastUpdateUtc { get; set; }         public byte Status { get; set; }         public bool Deleted { get; set; }         public DateTime? ActivatedUtc { get; set; }         public bool Test { get; set; }          public virtual ICollection<Reader> Reader { get; set; }         public virtual ICollection<Writer> Writer { get; set; }     } } 

Metadata (Both have to use the same namespace):

namespace CoreProject.Persistence.EFCore {     [ModelMetadataType(typeof(IUserMetadata))]     public partial class User : IUserMetadata     {         public string FullName => FirstName + " " + LastName;     }      public interface IUserMetadata     {         [JsonProperty(PropertyName = "Id")]         int UserId { get; set; }          [JsonIgnore]         string Password { get; set; }         [JsonIgnore]         string PasswordHashKey { get; set; }         [JsonIgnore]         byte Role { get; set; }     } }