Reference generic property in expression

Question

Let's say I have two Tables, Lunch and Dinner. I know that both contain the DateTime property "Time".

If I have a generic method GetTime, how could I return db.Lunch.Time when T is Lunch and db.Dinner.Time when T is Dinner? I'm trying to achieve this without testing for T individually using typeof, but rather generically.

Pseudocode:



public T GetTime<T>(DateTime dt)
{
    return MyDataContext.GetTable<T>().Where(entity => entity.Time == dt);
}

So when I call GetTime<Dinner> it will automatically look in the Dinner Table for all dinner entities with the property time equal to my supplied parameter dt.

The problem is that I can't specifiy entity.Time in my expression because T is a generic. My question is how to get around that, so that I can look for any T (knowing that all my entities in fact have the Time property) without having to create specific methods for Dinner and Lunch.

This question is rather confusing. A code sample or some pseudo-code would help. — Philippe Leybaert
– Philippe Leybaert, Commented Jun 1, 2009 at 20:25
Remember, generics are not templates. Everything you do with the type parameter has to be resolvable based solely on the constraints on the type parameter. — Eric Lippert
– Eric Lippert, Commented Jun 1, 2009 at 22:40

BFree · Accepted Answer · 2009-06-01 20:35:19Z

5

You'd have to have both classes implement an interface something like this:

public interface IMyInterface
{
   DateTime Time{get;set;}
}

And then in your generic method:

public void MyMethod<T>(T item) where T: IMyInterface
{
    //here you can access item.Time
}

answered Jun 1, 2009 at 20:35

BFree

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CSharpAtl · Accepted Answer · 2009-06-01 20:41:07Z

1

You could use an interface that Lunch and Dinner implement that has a property called Time

 public interface IMealTime
    {
        DateTime Time { get; set; }
    }

    public class Lunch : IMealTime
    {
        #region IMealTime Members

        public DateTime Time { get; set; }

        #endregion
    }

    public class Dinner : IMealTime
    {
        #region IMealTime Members
        public DateTime Time { get; set; }

        #endregion
    }

    public class GenericMeal
    {
        public DateTime GetMealTime<T>(T meal) where T: IMealTime
        {
            return meal.Time;
        }
    }

answered Jun 1, 2009 at 20:41

CSharpAtl

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1 Comment

Alex Over a year ago

Great explanation. Came after the first answer in the same direction, but anyways thank you. :)

Marcel Popescu · Accepted Answer · 2009-06-01 20:31:50Z

0

You can always use reflection, of course. Also, if the two types implement a common interface with a Lunch property, you can use that. (I do not understand what you mean by "Table" here.)

answered Jun 1, 2009 at 20:31

Marcel Popescu

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