Using statement without curly braces

Question

I'm looking at the Npgsql getting started examples and having a hard time understanding the use of the using statement.

var connString = "Host=myserver;Username=mylogin;Password=mypass;Database=mydatabase";

await using var conn = new NpgsqlConnection(connString);
await conn.OpenAsync();

// Insert some data
await using (var cmd = new NpgsqlCommand("INSERT INTO data (some_field) VALUES (@p)", conn))
{
 cmd.Parameters.AddWithValue("p", "Hello world");
 await cmd.ExecuteNonQueryAsync();
}

Why would one add "using" to the declaration of conn variable?

await using var conn = new NpgslConnection(connString);

Also, as there is no curly braces, why is conn not disposed before it is being used when inserting data in the following line?

await using (var cmd = new NpgsqlCommand("INSERT INTO data (some_field) VALUES (@p)", conn))

When will it be disposed?

Answer 1

using adding for guarantee what your connection will be close after transaction

await using var conn = new NpgslConnection(connString);

On your last question.

With the new C# 8 using declaration, the code with the using statement can be simplified. Curly brackets are no longer needed. At the end of the scope of the variable r (which is here the end of the method), the Dispose method is invoked. Here, the compiler also creates a *try/finally block to make sure Dispose is called if errors occur.