Using generics to build generic data logic layers

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 ) ;

 

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