面向对象的Linq2Sql查询类

Question

For my internship I'm creating a program that communicates with a database on the background. The program is layered in the MVC(Model-View-Controller) way.

For the View I want to access the data through something I called the DataAccesLayer(DAL). Because that view has minimal knowledge I want it to pass an ID for the query I want to call. The calling will be done inside the DAL. Then with the ID I want to ask a class that holds the queries to return the query to then execute it inside the DAL. Picture for visualizing.

The problem I have now is how to execute the query in my Read function. The code for DAL is the following:

public class DataAccesLayer
{
    private Queries queryloader;
    private RoadsoftDigitacV8DataContext db;

    public DataAccesLayer()
    {
        queryloader = new Queries();
        db = new RoadsoftDigitacV8DataContext();
    }

    public List Read(int ID)
    {
        IQueryable query;
        query = queryloader.GetQuery(ID);

        return query.ToList();

    }

}

The Code for the Queries class:

public class Queries
{
    private Dictionary<int, IQueryable object> queryDict;
    private ErrorLoggerWinLog logger;

    public Queries()
    {
        logger = ErrorLoggerWinLog.Instance();
        queryDict = new Dictionary<int, IQueryable object>();
        queryDict.Add(1, from d in db.Drivers
                         select d);
    }

    public object GetQuery(int ID)
    {
        var query;
        if(queryDict.TryGetValue(ID, out query) == false)
        {
            logger.WriteLine("Queries", "Could not find the query specified", ErrorLoggerWinLog.loggerlevel.Error);
        }
        return query;
    }
}

I'm wondering, is this possible? Right now it doesn't seem to work. I'm probably forgetting something or missing something important. Does anyone have any experience with this kind of set-up, or should be looking at a totally different solution?

Edit: Right now it doesn't seem to execute the query, like I'm missing a command in the read function. The Datacontext is filled though, that's being done in a different section of the program.

Edit2: Right now I'm looking into the IRepository Pattern, it's a great learning experience, Thank you all who took time to comment and anwser!

Answer 1

At any time your queryDict has only one element; the only time that GetQuery() doesn't log an error message and doesn't return null is when you pass 1 to it. as a consequence Read(1) returns a list of all Drivers, otherwise throws a NullReferenceException because, well, query is null.

You should use something like this:

    public class DriversDAL
    {
        private RoadsoftDigitacV8DataContext db;

        public DriversDAL()
        {
            db = new RoadsoftDigitacV8DataContext();
        }

        public Driver GetDriver(int ID)
        {
            return db.Drives.Single(d => d.ID == ID);
        }

    }

If you want a generic solution, you should use a generic dao and the Repository pattern:

How To Create Generic Data Access Object (DAO) CRUD Methods with LINQ to SQL