EF Table-Per-Type：将新的子代添加到现有父代

Question

I'm new with ASP.NET MVC Code First, I have implemented a table-per-type hierarchy that goes something like this:

public abstract class Request
{
    public int RequestId {gets;set;}
    public DateTime CreationDate {get;set;}
    public string CreatedBy {gets;set;}
    public bool Active {Get;set;}
}

public class RequestChildA : Request
{
    public string RequestChildAProp1 {get;set;}
    public string RequestChildAProp2 {get;set;}
    ...
}

public class RequestChildB : Request
{
    public string RequestChildBProp1 {get;set;}
    public string RequestChildBProp1 {get;set;}
    ...
}


Request table
+---------------+-------------------------+------------+--------+
|    RequestId  |       CreationDate      |  CreatedBy | Active | 
+---------------+-------------------------+------------+--------+
| 1             | 2019-08-19 09:40:39.817 | HydroFlask |    1   |
+---------------+-------------------------+------------+--------+

RequestChildA table
+---------------+-------------------------+---------------------+
|    RequestId  |   RequestChildAProp1    |  RequestChildAProp1 | 
+---------------+-------------------------+---------------------+
| 1             |         ValueA          |   ValueB            |
+---------------+-------------------------+---------------------+

ChildA and ChildB can share the same request. My question is how can I add a NEW ChildB to an existing Request that also has an existing ChildA.

I have tried the usual:

var childB = new childB { RequestChildBProp1 = "Value1", RequestChildBPro2 = "Value2" };
childB.RequestId = 1;
db.RequestChildB.Add(childB);
db.SaveChanges();

It is completed with no errors, but it creates a new Request. I need a new ChildB that is the same RequestId as the existing. Please help!

My design might be wrong, please bear with me. Thank you!

Answer 1

Try the following, not tested:

public class Request
{
    public int RequestId {gets;set;}
    public DateTime CreationDate {get;set;}
    public string CreatedBy {gets;set;}
    public bool Active {Get;set;}
}

public class RequestChildA
{
    public string RequestChildAProp1 {get;set;}
    public string RequestChildAProp2 {get;set;}
    ...
    public virtual Request Request {get; set;}

}

public class RequestChildB
{
    public string RequestChildBProp1 {get;set;}
    public string RequestChildBProp1 {get;set;}
    ...
    public virtual Request Request {get; set;}
}

Answer 2

I think what you need is creating your RequestChildA and RequestChildB like this:

public class RequestChildB
{
    public virtual Request Request {get;set;}

    public string RequestChildBProp1 {get;set;}
    public string RequestChildBProp1 {get;set;}
}

and insert data like this:

db.RequestChildB.Add(new RequestChildB
{
    Request = db.Request.Find(1),
    //...other properties
});

db.SaveChanges();