Question

I am using LINQ and am having a hard time understanding how I can make new ‘domain model’ classes work within LINQ while querying across tables. I am using Linq to SQL, and C# in .NET 3.5.

Suppose I want an Extended Client class:

public class ExtendedClient  {     public int ID { get; set; }     public string Name { get; set; }     public string strVal { get; set; } } 

and in my data layer, I want to populate this from two tables (dc is my DataContext):

public ExtendedClient getExtendedClient(int clientID) {     var c = dc.GetTable<tClient>();     var cs = dc.GetTable<tClientSetting>();     var q = from client in c             join setting in cs             on client.ClientID equals setting.ClientID             where client.ClientID == clientID             select new ExtendedClient { client, setting.strValue };     return q;    } 

I am trying to return the row in the table tClient plus one extra column in tClientSetting.

The annoying errors I get are : Cannot initialize type ‘ExtendedClient’ with a collection initializer because it does not implement ‘System.Collections.IEnumerable’ and Cannot implicitly convert type ‘System.Linq.IQueryable’ to ‘ExtendedClient’. An explicit conversion exists (are you missing a cast?)

I realize this is a basic error, but I cannot determine how BEST to implement the IEnumerable because I cannot find an example.

Do I have to do this every time I want a specialized object? Thanks in advance.

Answer 1

public ExtendedClient getExtendedClient(int clientID) {     var c = dc.GetTable<tClient>();     var cs = dc.GetTable<tClientSetting>();     var q = from client in c             join setting in cs             on client.ClientID equals setting.ClientID             where client.ClientID == clientID             select new ExtendedClient { ID = client.ClientID, Name = client.Name, strVal = setting.strValue };     return q.Single(); } 

You’ll have to do a similar thing every time you need to return a specialized object. If you don’t need to return it, you don’t have to specify the type and you won’t need a special class. You could use anonymous types:

from client in c join setting in cs on client.ClientID equals setting.ClientID where client.ClientID == clientID select new { ID = client.ClientID, Name = client.Name, strVal = setting.strValue };