Question

I’m working to move my simple asp.net website to a three layer architecture. Currently I have Linq queries like the one below in my code-behind files. Basically this code snippet retrieves a collection of customer data from the database and then binds it to a grid control.

I’m wondering if someone can guide me on how to rewrite this in order to move it to my newly-created data access layer. I’m thinking I will turn it into a class (e.g. GetUserBoxesByStatus()) that can be reused throughout the site.

            var boxes = from p in sbm.Packages
                    where p.UserID == CurrentUserId && p.StatusID > 1 && p.StatusID < 3
                    select new { p.PackageTag, p.PackageName, p.DateReceived, p.DateShipped };
        GridView1.DataSource = boxes;
        DataBind();

Some of the options that I’ve investigated but have not had success implementing are the following:

DataTable — returning a DataTable seems like the best solution but it also appears to require a lot of potentially unecessarry code to define a table (isn’t the data source already mapped in my Linq 2 Entities dbml?)

IEneuerable — I think I could pass an IEnumerable list between the layers but after reading many tutorials about Linq I’m still a little lost

DTO — Conceptually I think I understand what a DTO is but I am not clear on how to begin implementing this approach

POCO — Again, the concept seems logical enough but I don’t know how to put this into practice

I’m hoping someone here can look at my code example and propose how they would tackle this using one of the above or some other solution.

Answer 1

Create a class with the properties you need. Select into that class. Return a strongly-typed List (so that the query is actually performed in the DAL, not in your view). Bind your data source to the list.

public class PackageViewModel
{
   public string Tag { get; set; }
   public string Name { get; set; }
   public DateTime Received { get; set; }
   public DateTime Shipped { get; set; }
}

DAL

public List<PackageViewModel> GetUserBoxesByStatus( int userID, int minStatus, int maxStatus )
{
    return sbm.Packages
              .Where( p => p.UserID == userID
                            && p.StatusID > minStatus
                            && p.StatusID < maxStatus )
              .Select( p => new PackageViewModel
               {
                   Tag = p.PackageTag,
                   Name = p.PackageName,
                   Received = p.DateReceived,
                   Shipped = p.DateShipped
               })
              .ToList();
}