Question

I am using Entity Framework 4.3 and using Code Fist.

I have a class

public class User
{
   public int UserId{get;set;}
   public string UserName{get;set;}
}

How do I tell Entity Framework that UserName has to be unique when creating database table?
I would prefer to use data anotations instead of configuration file if possible.

Answer 1

Solution for EF4.3

Unique UserName

Add data annotation over column as:

 [Index(IsUnique = true)]
 [MaxLength(255)] // for code-first implementations
 public string UserName{get;set;}

Unique ID
,
I have added decoration [Key] over my column and done.
Same solution as described here: https://msdn.microsoft.com/en-gb/data/jj591583.aspx

IE:

[Key]
public int UserId{get;set;}

Alternative answers

using data annotation

[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
[Column("UserId")]

using mapping

  mb.Entity<User>()
            .HasKey(i => i.UserId);
        mb.User<User>()
          .Property(i => i.UserId)
          .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
          .HasColumnName("UserId");