Map Existing Entity with Existing Table in Entity FrameWork - entity-framework

Question

Is it possible to map existing tables with existing Entities in Entity frame work as like NHibernate doing.
For example. I have entity as
public class User
{
public Int64 userId { set; get; }
public String Username { set; get; }
public Int64 RoleId { set; get; }
}
public class Role
{
public Int64 roleId { set; get; }
public String roleName { set; get; }
public IList<User> listUser { set; get; }
}
I have Table as
Users with id,name,roleId
Roles with id,name.
Now I want to map both using XML files. Is it possible to map exiting tables with exiting Entities.

Answer 1

You have a few options:
1) Manage your mapping via the database first edmx file (see http://www.asp.net/mvc/tutorials/mvc-5/database-first-development/creating-the-web-application)
2) Start with the database first approach then move over to a code first like approach using the fluent api (see http://agilenet.wordpress.com/2011/04/11/entity-framework-4-1-rc-with-an-existing-database/)

Answer 2

Usual way of mapping in EF is data annotation attributes or fluent mapping (actually with NHibernate fluent mapping is also better, because it gives you compile-time checks). So, here is fluent mapping for your classes:
public class UserMapping : EntityTypeConfiguration<User>
{
public UserMapping()
{
ToTable("Users"); // Not necessary, EF will use this mapping by default
HasKey(u => u.userId);
Property(u => u.userId).HasColumnName("id");
Property(u => u.Username).HasColumnName("name");
Property(u => u.RoleId).HasColumnName("roleId");
}
}
public class RoleMapping : EntityTypeConfiguration<Role>
{
public RoleMapping()
{
ToTable("Roles"); // Not necessary, EF will use this mapping by default
HasKey(r => r.roleId);
Property(r => r.roleId).HasColumnName("id");
Property(r => r.roleName).HasColumnName("name");
HasMany(r => r.listUser)
.WithRequired()
.HasForeignKey(u => u.RoleId);
}
}
Just provide these mappings to your DbContext:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new UserMapping());
modelBuilder.Configurations.Add(new RoleMapping());
base.OnModelCreating(modelBuilder);
}
I suggest you to read MSDN article Configuring/Mapping Properties and Types with the Fluent API.
Side note - another article to read is Naming Guidelines, especially its Capitalization Styles part.