The type must be a Reference type in order to use it as Parameter 'Tentity' in the Generic type or method 'Dbset<Tentity>'

Question

I am trying to set up an Enum in ENTITY FRAMEWORK. But I am not succeeding.

My Context is like this:

public class MoradaWebContext : DbContext
{
 public DbSet<MeuEnum> Status { get; set; }
}

The Enum is like this:

public enum MeuEnum
{
        Aberta = 1,
        Fechada = 4,
        Aguardando = 5,
}

And I wanted to leave it configured in the mapping correctly. Even in the Bank. (I have to see how I will register it in the Bank)

But this error is returning:

The type must be a Reference type in order to use it as Parameter 'Tentity' in the Generic type or method 'Dbset'

I used as a reference this link: https://msdn.microsoft.com/en-us/library/hh859576(v=vs.113). aspx

Answer 1

Is not possible.

You need to pass a class to DbSet.

An Enum may be a property of a model, but never a model itself. That is, it is acceptable

public MeuModel 
{
    public MeuEnum Status { get; set; }
}

But what you’re trying to do is not valid.

Answer 2

You can make one class, that gets the Enum and that class is related to another that you need.

In other words, it will be a class where your primary key will be Enum.

I use the following code:

1. A Generic class, which receives the type of enum:

   public class EnumTable<TEnum>
       where TEnum : struct
   {
       public TEnum Id { get; set; }
       public string Nome { get; set; }
       public string Descricao { get; set; }
   
       protected EnumTable() { }
   
       public EnumTable(TEnum enumType)
       {
           if (!typeof(TEnum).IsEnum)
           {
               throw new Exception($"Argumento inválido do tipo {typeof(TEnum)}");
           }
   
           Id = enumType;
           Nome = enumType.ToString();
           Descricao = enumType.GetEnumDescription<TEnum>();
       }
   
       public static implicit operator EnumTable<TEnum>(TEnum enumType) => new EnumTable<TEnum>(enumType);
       public static implicit operator TEnum(EnumTable<TEnum> status) => status.Id;
   }
   

2. Two extension methods, to take the description and do the Seed:

         public static string GetEnumDescription<TEnum>(this TEnum item)
   => item.GetType()
          .GetField(item.ToString())
          .GetCustomAttributes(typeof(DescriptionAttribute), false)
          .Cast<DescriptionAttribute>()
          .FirstOrDefault()?.Description ?? string.Empty;
   
   
   
     public static void SeedEnumValues<T, TEnum>(this IDbSet<T> dbSet, Func<TEnum, T> converter)
   where T : class
     {
             Enum.GetValues(typeof(TEnum))
               .Cast<object>()
               .Select(value => converter((TEnum)value))
               .ToList()
               .ForEach(instance => dbSet.AddOrUpdate(instance));
     }
   

3. Your enum:

   public enum MeuEnum
   {
      [Description("Em Aberto")]
       Aberta = 1,
   
      [Description("Fechado")]
       Fechada = 4,
   
      [Description("Aguardando alguma coisa")]
       Aguardando = 5
   }
   

4. Your class, inheriting the generic class, informing your Enum:

   public class MeuEnumClass: EnumTable<MeuEnum>
   {
       public MeuEnumClass(MeuEnum enumType) : base(enumType)
       {
   
       }
   
       public MeuEnumClass() : base() { } //deve ser definido o construtor padrão para o EF
   }
   

5. Your Dbset:

   public DbSet<MeuEnumClass> Status { get; set; }
   

6. Overwrite the Seed method of the EF configuration class:

   protected override void Seed(SeuDbContext context)
   {
       context.Status.SeedEnumValues<MeuEnumClass, MeuEnum>(@enum => new MeuEnumClass(@enum));
   }
   

7. Ready. Create the migration and update the data set.

The table will be created with the fields Id, Name and Description where:

• Id: It is the PK and also the enum proper. (A whole shall be informed in the bank)

• Name: Is the Value of enum, for example "Open" in current code

• Description Is the value of the attribute Description informed on enum, for example "Open" in current code.

Code taken from: https://stackoverflow.com/a/44166999/4713574

I’m putting it to you as an answer in case someone might need something like this.