实体框架通过流畅的API继承了一对零的一对一关系配置

Question

I can't find an answer by searching through SO questions and by Googling around.

I have a very simple structure:

public class Employee
{
   property int Id { get; set; }

   property int Name { get; set; }
}

public class Developer : Employee
{
   property string Level { get; set; }
}

and I have two tables for this domain model:

create table Employees
(
    Id int not null primary key identity(1, 1),
    Name nvarchar(100) not null
)

create table Developers
(
    Id int not null primary key,
    Level nvarchar(100)
)

alter table Developers 
add constraint FK_Developers_Employees 
foreign key ([Id]) references Employees ([Id])

This C# model and SQL Server database schema can not be changed. The scenario is:

1. First add an employee ( One -employee)
2. This employee is not a developer yet (One-employee-to- Zero -developer)
3. Then promote that employee to a developer (One-employee-to- One -developer)

How should I configure my Context class? I would also appreciate sample code for this scenario.

Answer 1

You can not do this as simple as it seems. You have to delete the first entity from context, clone it in a new object - Developer here-, and add the new one to the context.

var emp = _context.Employees.Find(id);
_context.Delete(emp);
var dev = new Developer(/* clone from emp */);
_context.Developers.Add(dev);
_context.SaveChanges();

Which will change the Id of employee. However, if you want to avoid this (changing Id ), you have to use raw SQL - eg calling a stored procedure - to add a row to Developers and reload the context.

Another option is to set Id column by custom, which as you mentioned in Q, it's not possible to change the scheme. So ignore it.