How to map column names with EF 4.3.1?

I've got problem with simple mapping (using EF 4.3.1 - code first approach)

public class Someclass
     {
         public virtual int ID { get; set; }
         public virtual string Name { get; set; }
     } 
 

And Table someclass with int ID and varchar someclass_name.
Now what I want to do is map Name with someclass_name

 modelBuilder.Entity<Someclass>()
              .Property(r => r.Name).HasColumnName("someclass_name");
 

But id doesn't work and exception says: "context has changed since the database was created. Consider using Code First Migrations to update the database (http://go.microsoft.com/fwlink/?LinkId=238269)."

I've also tried doing that by:

modelBuilder.Configurations.Add(new SomeclassMap());
 
 public class SomeclassMap : EntityTypeConfiguration<Someclass>
     {
         public SomeclassMap() {
           //  this.Property(r => r.Name).HasColumnName("someclass_name");
             Map(r =>
             {
                 Property(m => m.Name).HasColumnName("restaurant_name");
             });
         }
     }
 

Can somebody tell me what am I doing wrong? THX

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