实体框架在使用 AutoMapper 后分离虚拟对象

Question

I have set up an MVC environment where I am taking an Entity Framework entity, mapping it to a DTO for the user to modify and then mapping the DTO back to the EF entity.

My EF classes are as follows:

public class Person
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public int AddressId { get; set; }
    public virtual StreetAddress Address { get; set; }
    /*More stuff here*/
}
//For the purpose of this example lets assume that addresses cannot be changed, they are read-only
public class StreetAddress
{
    [Key]
    public int Id { get; set; }
    public string StreetName { get; set; }
    /*More stuff here*/
}

My DTO is:

public class PersonDTO
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int AddressId { get; set; }
    public StreetAddress Address { get; set; }
    /*More stuff here*/
}

From here I map the Person to a PersonDTO and back again:

Person person = /*retrieve from database*/;
PersonDTO dto = Mapper.Map<PersonDTO>(person);

// send dto to user, user updates name, user sends dto back
// the address object is the same, but it might have been converted to JSON or something like that during transport

Person person = Mapper.Map<Person>(dto);

So I now have a Person ready to save to the database. The StreetAddress object still has the same information, however now EF sees the Address as detached. I can't use context.Attach(Address) because the context already has a StreetAddress with the same Key attached, and attempting to do so causes an exception to be thrown.

If I choose to ignore the detached Address and add this new person to my database, EF sees the Address as a brand new object and inserts it into the database, causing the address row in the database to be duplicated, same details, new ID.

My current solution is to replace the Address object with the one that is already attached to the context:

var tracked = context.ChangeTracker.Entries<Address>();
person.Address = tracked.Where(x => x.Entity.Id == person.AddressId).Select(e => e.Entity).FirstOrDefault();

Is there a better way to do this? perhaps a way to tell EF that if there is a Person with an Address where the Address ID is already in the database there is no need to insert it?

Answer 1

One way is to expose your FK AddressId in Person and PersonDTO.

Another is to set the entity state to modified: context.Entry(person.Address).State = EntityState.Modified; as shown here