Question

I’m struggling while trying to write generic methods to save and load data from a Sterling database.

This is my save method:

public static void SaveList<T>(List<T> listToSave)
{
    foreach (T listItem in listToSave)
    {
        DatabaseInstance.Save(listItem);
    }
}

I get squiggly red line under save and an error of “The Type T must be a reference type in order to use it as parameter T”

This is my load method:

    public static List<T> LoadList<T>()
    {
        List<T> list = (from index in DatabaseInstance.Query<T, int>() select index.Key).ToList();

        return list;
    }

I get the same error.

Any ideas?

Cheers

Steve

UPDATE:

I added a where T : class as suggested and got an error:

The Type T must have a public parameterless constructor in order to use it as a parameter

Following instructions in the link provided by Bryan I added , new() on the end and all working now.

Answer 1

You need a generic type constraint on your definition:

public static void SaveList<T>(List<T> listToSave) where T : class
{
    foreach (T listItem in listToSave)
    {
        DatabaseInstance.Save(listItem);
    }
}

public static List<T> LoadList<T>()  where T : class
{
    List<T> list = (from index in DatabaseInstance.Query<T, int>() select index.Key).ToList();
    return list;
}