Using generics to build generic data logic layers
Consider exposing raw Generic collections from your data logic layers, such
as:
public class PersonManager {
...
public List<Person> ListPeople(...) { ... } ;
}
When I started messing around with building applications in 2.0 I quickly
wrapped Generic collections like so:
public class PersonCollection : List<Person> {
...
}
This was normally done so that I could hang a Sort method off of them:
public class PersonCollection : List<Person>, IBidirectionalSort {
...
public void Sort( string sortExpression, bool isAscending ) { ... }
}
The downside of this approach is that you end up writing fiddly code around
calls to generic helper methods.
As an example, let's say that I write a nice generic helper method to page my
collections:
public static void Page(ref List<T> data, int maximumRows, int startRowIndex)
where T : IDataObject, new() {
if (data.Count > 0) {
if (maximumRows > 0 && startRowIndex >= 0) {
List<T> tmpColl = null;
int remainingRowCount = data.Count - startRowIndex;
int count = (remainingRowCount >= maximumRows) ? maximumRows : remainingRowCount;
if (count > 0) {
tmpColl = new List<T>();
tmpColl.AddRange(data.GetRange(startRowIndex, count));
}
data = tmpColl;
}
}
}
If I’ve wrapped my collection – as per the PersonCollection example – then
using the generic Page method will require temporary object creation when I’m
calling it, something like:
public PersonCollection ListPeople(...) {
...
PersonCollection people = FillList( reader ) ;
List<Person> tmp = Page( people, 20, 0 ) ;
PersonCollection peopleToReturn = new PersonCollection() ;
peopleToReturn.AddRange( tmp ) ;
return peopleToReturn ;
}
So, you can see that by the time we have many generic methods, working with
temporary objects becomes cumbersome. Exposing List<Person> from
this method would lead you to build your surrounding methods – such as FillList
and Page – to work with your code better but will also lead to leaner code:
public List<Person> ListPeople(...) {
...
List<Person> people = FillList<Person>( reader ) ;
return Page<Person>( people, 20, 0 ) ;
}