DataTable to List <T> 转变

Question

Is there any better way than the following?

Particularly, I want to replace Activator with something else.

public static List<T> ToList<T>(DataTable dt)
        {
            Type type = typeof(T);

            List<T> list = new List<T>();

            foreach (DataRow dr in dt.Rows)
            {
                object[] args = new object[1];

                args[0] = dr;

                list.Add((T)Activator.CreateInstance(type, args));
            }

            return list;
        }

Answer 1

The first thing I want to mention is that you probably don't need a list. Odds are, an IEnumerable is enough. Even if you do need a list, it's trivial to convert an IEnumerable to a list.

With that in mind, this code is a nice generic way to accomplish it:

public static IEnumerable<T> ToEnumerable<T>(DataTable dt, Func<DataRow, T> translator)
{
    foreach(DataRow dr in dt.Rows)
    {
       yield return translator(dr);
    }
}

Hopefully you can see how re-usable this is. All you need to do is supply a function that knows how to convert an individual DataRow into your T type. That function might use Activator, but it doesn't have to. It might just use a normal constructor and set a few properties.

Answer 2

I don't really see any way to improve this code - why do you want to avoid Activator ?

One option you could explore would be to create some sort of interface like this:

interface IFoo
{
    void Initialize(DataRow dr);
}

And then implement this interface on any type that gets passed to this method. Then you would constrain your generic type parameter like this:

public static List<T> ToList<T>(DataTable dt)
    where T : IFoo, new()

Then change the implementation of your method like this:

public static List<T> ToList<T>(DataTable dt)
    where T : IFoo, new()
{
    List<T> list = new List<T>();

    foreach (DataRow dr in dt.Rows)
    {
        T t = new T();
        t.Initialize(dr);
        list.Add(t);
    }
    return list;
}

Answer 3

One thing I'd add to Andrew's answer is if you go that route you can (sorta) avoid the Activator class by constraining the generic method with a new() constraint.

public static List<T> ToList<T>(DataTable dt)
    where T : IFoo, new()
{
    ...
    foreach ( ... ) {
       var foo = new T();
       foo.Initialize(dataRow);
       list.Add(foo);
    }
    ...
}

The reason I say "sorta" is because C# actually just compiles that into an Activator.CreateInstance call at compile-time anyway. But it looks much cleaner.