实体框架代码首先不保存后延迟加载

Question

I have a lookup table and a data table in my db. I'll use gender and person for an example. So let's say the gender table looks like so:

Id         Code
1          Male
2          Female

and the person table looks like so:

Id         Name             GenderId
1          Bob              1
2          Jane             2

I've modelled both tables in EF code first like so:

public class Gender
{
    public int Id {get;set;}
    public string Code {get;set;}
}

public class Person
{
    public int Id {get;set;}
    public string Name {get;set;}
    public int GenderId {get;set;}

    public virtual Gender {get;set;}
}

If I read a person already in the DB then I can access person.Gender.Code without a problem. If I do this:

var person = new Person
             {
                 Name = "Bob",
                 GenderId = 1,
             };

context.People.Add(person);
context.SaveChanges();

var code = person.Gender.Code;

Then it will save correctly but will fail on the last line as gender is null. If I then open a new context and load the saved entity then the last line works fine. Is there a way that I can access gender directly after a save as if I just loaded the entity from the DB?

Answer 1

Your problem is that when you use new Person() it will just create a POCO object which doesn't know how to get the it's Gender property. So to make the lazy loading work you need proxies .

You can create your person as a proxy with DbSet.Create() :

var person = context.People.Create();
person.Name = "Bob";
person.GenderId = 1;

context.People.Add(person);
context.SaveChanges();