将DataRow转换为对象

Question

I've created generic List and populate with some objects. Then List I mentioned before converted into DataTable to use in DataGridView. Problem is when I want get Row from this grid I have DataRow. I wanted to convert this to my object againt but not sure how to do it. Maybe you could give some example?

Thanks

Answer 1

Well, if you can't or won't use an "ORM" (object-relational mapper, like Linq-to-SQL or NHibernate - that's exactly what these tools do, and do quite well for you), you'll have to do this yourself.

Converting a DataRow into a domain object model is pretty boring code, really:

public Customer ConvertRowToCustomer(DataRow row)
{
   Customer result = new Customer();

   result.ID = row.Field<int>("ID");
   result.Name = row.Field<string>("CustomerName");
   ..... // and so on

   return result;
}

The biggest challenge here is making this rock-solid and handling (or avoiding) all possible errors (like a field being NULL etc.).

Another possibility would be to have a constructor on your domain model object type that would take a DataRow as parameter and construct a new object from it.

Marc

Answer 2

Assuming you're using a class MyObject , defined as follows :

class MyObject
{
    public string Foo { get; set; }
    public int Foo { get; set; }
}

You could do something like that :

using System.Data.DataSetExtensions;

...

List<MyObject> list = (from row in table.AsEnumerable()
                       select new MyObject
                       {
                            Foo = row.Field<string>("foo"),
                            Bar = row.Field<int>("bar")
                       }).ToList();

Answer 3

Why not just put your objects into a BindingList<> rather than a List<>? Then you can skip the converting to DataTable and back again exercise. You may need to implement INotifyPropertyChanged on your objects, but once they are inside a BindingList, changes in the datagrid will automatically be applied to your underlying objects.

Sorting can be handled by either sorting the list manually on column header click, or by inheriting from BindingList<> and implementing the sorting functionality inside it - then clicking on a header automatically sorts the list - no code required.

Answer 4

Well nowadays it is easier using ORMs of course. But if still you're using the old fashion you can go with a pretty easy Extension Class to do the job for you using a little bit of reflection and generic methods and lambda as follows:

public static class MapperExtensionClass
{

        public static IEnumerable<MyClassType> ToMyClassTypeEnumerable(this DataTable table)
        {
            return table.AsEnumerable().Select(r => r.ToMyClassType());
        }

        public static MyClassType ToMyClassType(this DataRow row)
        {            
            return row.ToObject<MyClassType>();
        }

        public static T ToObject<T>(this DataRow row) where T: new()
        {
            T obj = new T();
            foreach (PropertyInfo property in typeof(T).GetProperties())
            {
                if (row.Table.Columns.Contains(property.Name))
                {
                    property.SetValue(obj, property.PropertyType.ToDefault(row[property.Name]));
                }
            }

            return obj;
        }


        public static object ToDefault(this Type type, object obj)
        {
            if (type == null)
                throw new Exception("Customized exception message");

            var method = typeof(MapperExtensionClass)
                .GetMethod("ToDefaultGeneric", BindingFlags.Static | BindingFlags.Public);

            var generic = method.MakeGenericMethod(type);

            return generic.Invoke(null, new object[] { obj });            
        }

        public static T ToDefaultGeneric<T>(object obj)
        {
            if (obj == null || obj == DBNull.Value)
            {
                return default(T); 
            }
            else
            {
                return (T)obj;
            }
        }
}

You should also remember GridView objects can bind a lot of data source types. So it is your decision from a design point about what you should go with.