How can I update my DTO's ID when inserting multiple new entities - entity-framework

Question

I'm using EF4. I'm adding a series of new entities from a list of DTOs, and I'm not saving changes until after all of them are added. I'm wanting to set the IDs of the DTOs to what the new entities' IDs are. How on earth do I do this? Does EF provide a mechanism for this?
With a single entity I would do this:
public void InsertMyDto(MyDto a_dto)
{
var newEntity = new MyEntity
{
Name = a_dto.Name,
Type = a_dto.Type.ToString(),
Price = a_dto.Price
};
_dataContext.MyEntities.AddObject(newEntity);
_dataContext.SaveChanges();
a_dto.ID = newEntity.ID;
}
This works fine, but what do I do in this case?
public void InsertMyDtos(IEnumerable<MyDto> a_dtos)
{
foreach (var myDto in a_dtos)
{
var newEntity = new MyEntity
{
Name = myDto.Name,
Type = myDto.Type.ToString(),
Price = myDto.Price
};
// Does some validation logic against the database that might fail.
_dataContext.MyEntities.AddObject(newEntity);
}
_dataContext.SaveChanges();
// ???
}
I want to save all at once, because I have validation work (not shown above) that is done against the database and fails before it gets to SaveChanges, and if it fails I want it to fail as a whole transaction (i.e. rollback).

Answer 1

I don't think that EF can help you here. It even can't help you for a single instance which forces you to write a_dto.ID = newEntity.ID. The counterpart of this code for multiple entites is to keep track of the pairs of dtos and new entities:
public void InsertMyDtos(IEnumerable<MyDto> a_dtos)
{
Dictionary<MyDto, MyEntity> dict = new Dictionary<MyDto, MyEntity>();
foreach (var myDto in a_dtos)
{
var newEntity = new MyEntity
{
Name = myDto.Name,
Type = myDto.Type.ToString(),
Price = myDto.Price
};
dict.Add(myDto, newEntity);
// Does some validation logic against the database that might fail.
_dataContext.MyEntities.AddObject(newEntity);
}
_dataContext.SaveChanges();
foreach (var item in dict)
item.Key.ID = item.Value.ID; // Key is MyDto, Value is MyEntity
}