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c#genericsgeneric-method

C# call Generic method dynamically


Given the following Interfaces:

interface IEntity
{
    int Id{get;}
} 

interface IPerson : IEntity
{
    string Name{get;} 
    int Age{get;}
}

interface ITeacher : IPerson 
{
    string StaffId{get;}
}

interface IStudent : IPerson 
{
    string StudentId{get;}
    string Courses{get;}
}

interface IRepository
{
    T Get<T>(int id) where T : IEntity
}

I have the following classes in my namespace

public class EntityBase() : IEntity
{
    int Id{get;set;}
}
public class Teacher : EntityBase, ITeacher{}
public class Sudent : EntityBase, IStudent{}

Currently I am implementing this IRepository as follows:

class Repository: IRepository
{
    IDataContext Context{get;set;}

    T Get<T>(int id) where T : EntityBase
    {
        if(typeof(T) == typeof(Teacher))
            return Context.Get<ITeacher>(id);
        if(typeof(T) == typeof(Sudent))
            return Context.Get<ISudent>(id);
        throw new Exception("Unknown Interface " + typeof(T).Name);
    }
}

Is there a betterway of implementing this? Given that our Context has no knowledge of our data types (Teacher, Student), just its interfaces (ITeacher, IStudent).

Can something like this work?

class Repository: IRepository
{
    T Get<T>(int id) where T : EntityBase
    {
        var MyInterface = FindInterface<T>();
        return Context.Get<MyInterface>(id);
    }
}

Solution

  • I think this will do:

    class Repository: IRepository
    {
        IDataContext Context{get;set;}
    
        T Get<T>(int id) where T : EntityBase    
        {
            string[] interfaceList = new string[] 
                { "ITeacher", "IStudent"};
    
            Type interfaceType = null;
            foreach (string s in interfaceList)
            {
                var types = typeof(T).FindInterfaces((x, y) => x.Name == y.ToString(), s);
    
                if (types.Length > 0)
                    interfaceType = types[0];
            }
    
            if (interfaceType == null)
                throw new Exception("Unknown Interface " + typeof(T).Name);
    
            MethodInfo method = typeof(Context).GetMethod("Get");
            MethodInfo generic = method.MakeGenericMethod(interfaceType);
    
            var returnValue = generic.Invoke(Context, new object[] { id });
    
            return (T)Convert.ChangeType(returnValue, typeof(T));
        }
    }
    

    EDIT: As I don't know the name of your namespace, I have used the Name property to filter the interfaces. In real world usage I will suggest that you use FullName just to be sure, like this:

    ...
    string[] interfaceList = new string[] 
                    { "MyNamespace.ITeacher", "MyNamespace.IStudent"};
    ...
    var types = typeof(T).FindInterfaces((x, y) => x.FullName == y.ToString(), s);