Entity Framework two tables with identical objects

Question

I have two tables that have identical properties, for example:

DbSet<Person> Students;
DbSet<Person> Teachers;

However Entity Framework does not allow the same class to be used for different tables.

So, instead I use:

DbSet<Student> Students;
DbSet<Teacher> Teachers;

public class Student : Person { }
public class Teacher : Person { }

However if I retrieve from a third party, a large set of data as

List<Person> data;

I am unable to do

Students.Add(data) <== compile time error unable to convert

nor

foreach (var item in data)
    Students.Add((Student)item); <== runtime error unable to cast

Any suggestions on a good way to handle this?

Note: this is a simplistic example it is actually used for large quantities of stock price bars and performance is a big issue and I don't necessarily want to be instantiating many, many copies of an object if I can help it.

yeah I'm not surprised this doesn't work. Even with the same properties, it won't know that it can convert Person to Student. One idea is to serialize Person to a json string, and then de-serialize it as a Student. It would take two lines of code, and should be fast, — Casey Crookston, Aug 22 '19 at 17:46
You could make a new interface, `IPerson`, and have `Student`, `Teacher`, and `Person` all implement `IPerson`. Then change your collection to a `List`. — Sam Axe, Aug 22 '19 at 18:35
Also, you can not add a collection to another collection with the `Add` method. `Add` expects a single element. What you want is the `AddRange` method. — Sam Axe, Aug 22 '19 at 18:37
You could use `ReinterpretCast` from [this answer](https://stackoverflow.com/a/42078952/2557128) but it is a type safety violation. — NetMage, Aug 22 '19 at 19:25

score 0 · Accepted Answer · answered Aug 22 '19 at 18:29

We need more details on how you create the List<Person> for a completely valid answer, but if you create it by adding Student and Teacher objects, then you should be able to cast the ones that actually are Students at runtime:

List<Person> people = new List<Person>();
people.Add(new Student());
people.Add(new Teacher());
foreach(Student student in people.OfType<Student>())
{
    Students.Add(student);
}

I would also make Person abstract so you are forced to use one of the concrete types.

Entity Framework two tables with identical objects

1 Answers1