Try-catch-finally with 'using' in ADO.NET

Question

I want to check if I'm correctly disposing of resources using Ado.NET. I'm not sure when the 'using' statement makes .Dispose() irrelevant.

Please bear in mind I'm aware I shouldn't hardcode my SQL commands, this is just for training purposes.

  internal void CreateTable(string connectionString)
        {
            using (var connection = new SqliteConnection(connectionString))
            {
                using (var tableCmd = connection.CreateCommand())
                {
                    connection.Open();

                    tableCmd.CommandText =
                        @"CREATE TABLE IF NOT EXISTS coding (
                        Id INTEGER PRIMARY KEY AUTOINCREMENT, 
                        Date TEXT, 
                        Duration TEXT
                        )";

                    try
                    {
                        int rowCount = tableCmd.ExecuteNonQuery();
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine(ex.Message);
                        throw;
                    }
                    finally
                    {
                        connection.Dispose();
                        tableCmd.Dispose();
                    }

                }

                // Console.WriteLine($"\n\nDatabase created! \n\n");
            }
        }
    }

Answer 1

The using block or the using expression (collectively know as using statements) are just syntactical sugar. They will be translated to a proper try-finally block. If you visit sharplab.io and copy-paste there the following code:

using System;
public class C 
{
    public void M() 
    {
        using (var disposable = new Disposable()) 
        {
            Console.WriteLine("Inside the using block");
        }
    }
}

public class Disposable : IDisposable 
{
  public void Dispose() 
  {
  }
}

then the decompile code will look like this:

public class C
{
    public void M()
    {
        Disposable disposable = new Disposable();
        try
        {
            Console.WriteLine("Inside the using block");
        }
        finally
        {
            if (disposable != null)
            {
                ((IDisposable)disposable).Dispose();
            }
        }
    }
}
public class Disposable : IDisposable
{
    public void Dispose()
    {
    }
}

For the sake of simplicity I have omitted the attributes.

---

The good news is that the compiler is smart enough to incorporate catch blocks into the generated code (instead of naively have two nested try blocks).

Source

using System;
public class C 
{
    public void M() 
    {
        using var disposable = new Disposable();        
        try 
        {
            _ = disposable.Get();
        }
        catch (DivideByZeroException)
        {
            Console.WriteLine("Something went wrong");
        }
        
    }
}

public class Disposable : IDisposable 
{
  public int Get() 
  {
      throw new DivideByZeroException();
  }
  public void Dispose() 
  {
  }
}

Decompiled

public class C
{
    public void M()
    {
        Disposable disposable = new Disposable();
        try
        {
            disposable.Get();
        }
        catch (DivideByZeroException)
        {
            Console.WriteLine("Something went wrong");
        }
        finally
        {
            if (disposable != null)
            {
                ((IDisposable)disposable).Dispose();
            }
        }
    }
}
public class Disposable : IDisposable
{
    public int Get()
    {
        throw new DivideByZeroException();
    }

    public void Dispose()
    {
    }
}