Design pattern for Data Access Layer

Question

You might feel this is homework, for that I am sorry. I have searched but couldn\'t find a proper answer.

So my question is:

I have several classes and each

Answer 1

Normally, if I can't use any existing framework, I use both the Repository and Active patterns.

For simplicity, you could use only the Repository pattern. I normally define it like this:

public interface IEntity { }

//  Define a generic repository interface
public interface IRepository
    where TEntity : IEntity
{
    void Add(TEntity entity);
    void AddRange(IEnumerable entities);
    IEntity Get(TKey key);
    IEnumerable GetRange(IEnumerable keys);
    IEnumerable GetAll();
    //  ..., Update, Delete methods
}

//  Create an abstract class that will encapsulate the generic code
public abstract class Repository : IRepository
    where TEntity : IEntity
{
    protected Repository(/*parameter you may need to implement the generic methods, like a ConnectionFactory,  table name, entity type for casts, etc */) { }

    public override void Insert(IEntity entity)
    {
        //  do the insert, treat exceptions accordingly and encapsulate them in your own and more concise Exceptions, etc
    }
    //  ...
}

//  Create the entities classes, one for each table, that will represent a row of that table
public class Car : IEntity {/* Properties */}

//  Create a specific repository for each table
//  If the table have a composed key, just create a class representing it
public class CarRepository : Repository
{
    public CarRepository() {/* pass the base parameters */}

    // offer here your specific operations to this table entity
    public IEnumerable GetByOwner(PersonKey ownerKey)
    {
        //  do stuff
    }
}

Obviously, when doing your own implementations, you must take into account thread safety making good using of transactions, specially across diferent entity repositories.

//  simple example
ITransaction t = TransactionFactory.GetNewTransaction();
t.begin();
try{
    //  create person entity
    personRepository.Add(person, t);
    //  create cars assigned to person
    carRepository.AddRange(cars, t);
    t.commit();
}catch(Exception){
    t.rollback();
}

Just be sure that you really want to create your own DAL since it can end beeing extremelly complex, specially trying to develop the most generic solution.