Generate GUID for Primary key automatically In EF5 - asp.net

Question

I'm using Guids as primary key for the entities in my database, using the model binding feature of asp.net 4.5 web forms when im inserting a record in the database using entity framework 5 im doing something like
public void onInsert([Control("ControlID")] int? countryID){
if(countryID.hasValue){
var DbEntityToInsert = new DbEntity(); //where DbEntity is the class generated by the EF
TryUpdateModel(DbEntityToInsert);
DbEntityToInsert.GuidPK = Guid.NewGuid();
if(Page.ModelState.IsValid){
using(var db = new DatabaseContext()){
db.Add(DbEntityToInsert);
db.Save();
}//using ends
}//modelstate.isvalid if ends
}//countryid.hasvalue ends
}//main method ends
now i wanted to ask is there a way i can tell EF to generate a Guid for the PK while inserting a new record so i dont have to write the line
DbEntityToInsert.GuidPK = Guid.NewGuid();

Answer 1

You can try to override SaveChanges in your derived context. The main task is to find out if an entity has a GuidPK property as primary key. Here is an attempt using reflection:
public override int SaveChanges()
{
this.ChangeTracker.DetectChanges();
var addedEntities = this.ChangeTracker.Entries()
.Where(e => e.State == EntityState.Added)
.Select(e => new
{
Entity = e.Entity,
PropertyInfo = e.Entity.GetType().GetProperty("GuidPK")
})
.Where(x => x.PropertyInfo != null && x.PropertyInfo.CanWrite);
foreach (var x in addedEntities)
x.PropertyInfo.SetValue(x.Entity, Guid.NewGuid());
return base.SaveChanges();
}
To avoid reflection here you could have a common interface that is implemented by all your entities that use a GuidPK property as PK:
public interface IEntityWithGuidPK
{
Guid GuidPK { get; set; }
}
public class DbEntity : IEntityWithGuidPK
{
public Guid GuidPK { get; set; }
// ...
}
Then the code in SaveChanges could be:
//...
var addedEntities = this.ChangeTracker.Entries()
.Where(e => e.State == EntityState.Added &&
e.Entity is IEntityWithGuidPK)
.Select(e => e.Entity as IEntityWithGuidPK);
foreach (var e in addedEntities)
e.GuidPK = Guid.NewGuid();
//...