使用通用接口存储库

Question

I have my repositories setup like below.

interface IRepository<T> where T : DataRow
{
  T Get(int key);
}

interface ICartonRepository : IRepository<CartonDataRow>
{

}

class CartonRepository : ICartonRepository
{
  public CartonDataRow Get(int key)
  {

  }
}

I also have a PackRepository which is defined in the same way as the CartonRepository. What I would like to do is something like the following.

IRepository<DataRow> repository;
switch (rowType)
{
  case Carton:
    repository = new CartonRepository();
    break;
  case Pack:
    repository = new PackRepository();
    break;
}

Is there a way I can achieve this?

Answer 1

interface IRepository<out T> where T : DataRow
{
  T Get(int key);
}

This requires C# 4.0 though.

Answer 2

You require some sort of Factory pattern .

Following logic should go to Factory class

class RepositoryFactory
{
    IRepository<T>  Get(rowType)
    {
        IRepository<T> repository = default(IRepository<T>);
        switch (rowType)
        {
        case Carton:
            repository = new CartonRepository();
            break;
        case Pack:
            repository = new PackRepository();
            break;
        }

        return repository;
    }
}

You can further improve Get Method using Dependency Injection or based on maintaining all repositories in dictionary.

Answer 3

For C# 3.5 you will have to add the following:

public interface IRepository {
   DataRow Get(int key);
}

public abstract class Repository<T> : IRepository<T>, IRepository
    where T : DataRow
{
   public abstract T Get(int key);

   DataRow IRepository.Get(int key) {
       return this.Get(key);
   }
}

Then change CartonRepository to class CartonRepository : Repository<CartonDataRow> (I do not think you need ICartonRepository , but you can use it if you want). Then

IRepository repository;
switch (rowType)
{
  case Carton:
    repository = new CartonRepository();
    break;
  case Pack:
    repository = new PackRepository();
    break;
}