Question

I have three entities in my data context which inherit IFileData, but I want just a single delete method. How can this be achieved?

The code below give the error The type "IFileData" is not mapped as a Table.

    public void ImageDelete<T>(T instance) where T : class, IFileData
    {
        using (var db = this.CreateDataContext())
        {
            db.GetTable<T>().DeleteOnSubmit(instance);
            db.SubmitChanges();
        }
    }

The only solution I have so far is to do a switch on the .GetType() which is a bit messy.

Thanks!

Solution:

As Marc mentioned, I used dynamic in the calling method:

ImageDelete((dynamic)(instance as IFileData));

Answer 1

You could build the Expression manually, using the actual T ? Untested (since that Delete doesn’t exist?), but something like:

var param = Expression.Parameter(typeof(T), "x");
var lambda = Expression.Lambda<Func<T, bool>>(
    Expression.Equal(
       Expression.Property(param, "Key"),
       Expression.Constant(instance.Key)
    ), param);

This then isn’t bound to IFileData, but to T. It will fail, however, if IFileData.Key is implemented via explicit interface implementation – there must be an obvious Key field/property on T.

Then:

var table = db.GetTable<T>();
var obj = table.SingleOrDefault(lambda);
if(obj != null) table.DeleteOnSubmit(obj);
db.SubmitChanges();