Question

i am a new linq to sql learner and this is my very first attempt to create a data viewer program. The idea is simple, i’d like to create a software that is able to view content of a table in a database. That’s it.

I got an early problem here already and i have seen many tutes and articles online but I still cant fix the bug.

Here is my code:

    static void Main(string[] args)
    {
        string cs = "Data Source=localhost;Initial Catalog=somedb;Integrated Security=SSPI;";

        var db = new DataClasses1DataContext(cs);
        db.Connection.Open();

        foreach (var b in db.Mapping.GetTables())
            Console.WriteLine(b.TableName);

        Console.ReadKey(true);
    }

When I tried to check db.connection.equals(null); it returns false, so i thought i have connected successfully to the database since there is no error at all. But the code above doesn’t print anything out to the screen.

I kind of lost and don’t know what’s going on here. Does anyone know what is going wrong here?

Answer 1

Ok, let’s look at some of these lines:

---

var db = new DataClasses1DataContext(cs);

This is a perfectly normal and fine call to a constructor. Since DataContext implements IDisposable, when you are using it for real, consider using the using statement.

using (var db = new DataClasses1DataContext(cs))
{
  // do stuff with db here
} // when leaving the block, db is disposed - even in the case of an exception.

---

db.Connection.Open();

Don’t do this. DataContext will open and close the connection when it needs to.

---

foreach (var b in db.Mapping.GetTables())
  Console.WriteLine(b.TableName); 

Hmm, maybe there are no tables in the mapping. Did you drag a table onto the designer surface from the server explorer?

Most people would query a table instead of perusing the mappings. Consider this code instead:

foreach (var customer in db.Customer.Take(10))
{
  Console.WriteLine(customer.Name); 
}

---

Here’s a video showing how to drag a table onto the designer surface from the server explorer:

http://www.youtube.com/watch?v=z9L11qrw9gk