public UsersDataContext() :
        base(ConfigurationManager.ConnectionStrings["DBNameConnectionString"].ConnectionString, mappingSource)
        {
            OnCreated();
        }

------解决方案--------------------
C# code

public class DGService : IDGService
{
    public List <user> GetUsers()
    {
        SampleDCDataContext dc = new SampleDCDataContext();
        var query = from p in dc.users
                    select new user{ id = p.Id....};
        return query.ToList();
    }
}