Using custom attributes

Question

Hello, I am watching a video about [LINQ][1] and came across a problem. In this video, Mike uses some custom attributes for database name and that does not work for me.

My code (which works fine):

class MyContext : DataContext
{
    public MyContext(string conStr) : base(conStr)
    {
    }
}

class Program
{
    static void Main(string[] args)
    {
        MyContext ctx = new MyContext("server=.;database=AdventureWorks;Integrated Security=SSPI");
        Console.WriteLine(ctx.Connection.ConnectionString);
        ctx.ExecuteCommand("insert into _table (a, b) select {0}, {1}", "5", "B");

        Console.WriteLine("That's it!");
        Console.ReadLine();
    }
}

How I'd like it to be (notice the missing database parameter in creating of the object ctx and additional custom attribute for database name before the class MyContext):

[Database(Name="AdventureWorks")]
class MyContext : DataContext
{
    public MyContext(string conStr) : base(conStr)
    {
    }
}

class Program
{
    static void Main(string[] args)
    {
        MyContext ctx = new MyContext("server=.;Integrated Security=SSPI");
        Console.WriteLine(ctx.Connection.ConnectionString);
        ctx.ExecuteCommand("insert into _table (a, b) select {0}, {1}", "5", "B");

        Console.WriteLine("That's it!");
        Console.ReadLine();
    }
}

This throws exception 'invalid object name _table', just like I wouldn't define any database name. Am I missing something? It's my first time using custom attributes,...

Answer 1

You still need to read the attribute. You'll have to use reflection to parse the value in your myContextConstructor.

Answer 2

Looking at the context created from VS using the designer it has a static member in the class:

private static System.Data.Linq.Mapping.MappingSource mappingSource = new AttributeMappingSource();

here the the beginning of the Context class:

 [Database(Name = "Blah")]
    public partial class TestDataContext : System.Data.Linq.DataContext
    {

     private static System.Data.Linq.Mapping.MappingSource mappingSource = new AttributeMappingSource();

    #region Extensibility Method Definitions
    partial void OnCreated();
    partial void InsertAdmin(Admin instance);
    partial void UpdateAdmin(Admin instance);
    partial void DeleteAdmin(Admin instance);
    partial void InsertUser(User instance);
    partial void UpdateUser(User instance);
    partial void DeleteUser(User instance);
    #endregion

     public TestDataContext() : 
       base(global::TestStuff.Properties.Settings.Default.FraudAnalystConnectionString, mappingSource)
     {
      OnCreated();
     }

     public TestDataContext(string connection) : 
       base(connection, mappingSource)
     {
      OnCreated();
     }

     public TestDataContext(System.Data.IDbConnection connection) : 
       base(connection, mappingSource)
     {
      OnCreated();
     }

     public TestDataContext(string connection, System.Data.Linq.Mapping.MappingSource mappingSource) : 
       base(connection, mappingSource)
     {
      OnCreated();
     }

     public TestDataContext(System.Data.IDbConnection connection, System.Data.Linq.Mapping.MappingSource mappingSource) : 
       base(connection, mappingSource)
     {
      OnCreated();
     }

that is just the constructors...not the whole class...but to see for yourself just drag on a table from your Server Explorer after choosing to create Linq to Sql Classes template.