Question

Is the following defensive programming?

What I mean is that if it loses the connection, or some problem occurs during run-time and then the user runsit again will the .NET framework have tidied up any open connections and objects that were created when it first ran?

I’ve heard mention of a “Singleton pattern” – is this something I should use in the static method CreateConnection?

class Program {
  static void Main(string[] args) {
     DataTable CasTable = fillSampleDataTable("SELECT top 100 * FROM x");
     //do other stuff
  }


  static SqlConnection CreateConnection() {
     SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["XXX"].ConnectionString);
     return conn;
  }
  static SqlDataAdapter CreateAdapter(string myCommand) {
    SqlDataAdapter myAdapt = new SqlDataAdapter(myCommand, CreateConnection());
    return myAdapt;
  }
  static DataTable fillSampleDataTable(string myCommand) {
      using (var adapt = CreateAdapter(myCommand)) {                   
            DataSet mySet = new DataSet();
            adapt.Fill(mySet, "SampleData");
            return mySet.Tables["SampleData"];
    }
  }
 }

Answer 1

I would recommend you using the ADO.NET connection pool, a.k.a disposing the connections as soon as you have finished using them => wrap all IDisposable resources in using statements:

class Program 
{
    static void Main(string[] args) 
    {
        DataTable CasTable = fillSampleDataTable("SELECT top 100 * FROM x");
        //do other stuff
    }

    static DataTable fillSampleDataTable(string myCommand) 
    {
        var connectionString = ConfigurationManager.ConnectionStrings["XXX"].ConnectionString;
        using (var conn = new SqlConnection(connectionString))
        using (var cmd = conn.CreateCommand())
        using (var adapt = new SqlDataAdapter(cmd, conn)) 
        {
            conn.Open();
            cmd.CommandText = myCommand;
            DataSet mySet = new DataSet();
            adapt.Fill(mySet, "SampleData");
            return mySet.Tables["SampleData"];
        }
    }
}

But normally DataSets and DataTables are artifacts of the past. Today you are better off using strongly typed models.

So define a model:

public class MyModel
{
    public int Id { get; set; }
    public string Name { get; set; }
}

and then write a method that will return a list of those models:

class Program 
{
    static void Main(string[] args) 
    {
        var models = SelectTop100Models("SELECT top 100 * FROM x");
        //do other stuff
    }

    static IEnumerable<MyModel> SelectTop100Models() 
    {
        var connectionString = ConfigurationManager.ConnectionStrings["XXX"].ConnectionString;
        using (var conn = new SqlConnection(connectionString))
        using (var cmd = conn.CreateCommand())
        {
            conn.Open();
            cmd.CommandText = "SELECT top 100 * FROM x";
            using (var reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    yield return new MyModel
                    {
                        Id = reader.GetInt32(reader.GetOrdinal("ID")),
                        Name = reader.GetString(reader.GetOrdinal("Name")),
                    };
                }
            }
        }
    }
}

Alternatively you might consider using an ORM framework such as the ADO.NET Entity Framework as it will simplify you querying the relational database and working directly with your strongly typed models using LINQ queries.