Access to generic instance property

Question

How can I access to the Id property of the instance? I have the following code:

public void InsertOrUpdate(Book book)
{
    if (book.Id == default(int)) {

And I want to make it generic now:

public class TheRepository<T> : IRepository<T> where T : class
{
    public void InsertOrUpdate(T instance)
    {
        if (instance.Id == default(int))//How can I access Id here
        {
            context.Set<T>().Add(instance);

I searched for similar posts and I think I should write something like instance.GetType().GetProperty("Id").GetValue() but I don't know how exactly?

Answer 1

You could do a hack like this. Define an interface with only one property of type int called Id:

interface IHaveId
{
    public int Id { get; set; }
}

Then state that you entity implements the interface:

public class Book : IHaveId

Last state that the type used in your generic Repository class should implement this interface.

public class TheRepository<T> : IRepository<T> where T : class, IHaveId
{
    public void InsertOrUpdate(T instance)
    {
        if (instance.Id == default(int))
        {
            context.Set<T>().Add(instance);
        }
    }
}

Doing so you avoid the use of reflection, which is very expensive in general terms. Furthermore, your code now is more clear.