SOlID-DRY

DRY - Do Not Repeat Your Self Principle

Repartition is the root of all software evil

"Every piece of knowledge must have a single, unambiguous representation in the system"

"Repetition in logic calls for abstraction. Repletion in process calls for automation"

private static void Load()
    {
        using (var myConnection = new SqlConnection())
        {
            myConnection.ConnectionString = "Data Source=localhost;initial Catalog=someCatalog;Integrated Security=True";
            string myQuery = "";
            using (var myCommand = new SqlCommand(myQuery, myConnection))
            {
                myCommand.Parameters.Add(new SqlParameter("LastRunDate", new DateTime(1997, 1, 1)));
                var myAdapter = new SqlDataAdapter(myCommand);
                _invoiceTable = new DataTable("Invoices");
                myAdapter.Fill(_invoiceTable);
                foreach (DataRow row in _invoiceTable.Rows)
                {
                    Console.WriteLine("{0}--{1}--{2}", row[0], row[1], row[2]);
                }
            }
        }
        using (var myConnection = new SqlConnection())
        {
            myConnection.ConnectionString = "Data Source=localhost;initial Catalog=someCatalog;Integrated Security=True";
            string myQuery = "";
            using (var myCommand = new SqlCommand(myQuery, myConnection))
            {
                var myAdapter = new SqlDataAdapter(myCommand);
                _employeeTable = new DataTable("Employee");
                myAdapter.Fill(_employeeTable);
                foreach (DataRow row in _employeeTable.Rows)
                {
                    Console.WriteLine("{0}--{1}", row[0], row[1]);
                }
            }
        }
    }

Above you can see an example of a function that violates the DRY principle: can see an almost copy pasted code repeats it self

Analysis

• Magic strings/Values
• Duplicate logic in multiple locations
• Repeated if-then logic
• conditionals instead of polymorphism
• Repeated execution patterns
• Lots of duplicate, probably copy-pasted, code
• Only manual tests
• Static methods everywhere

Re factor to some of the DRY problems

• Magic strings/Values
  • Use configuration file like web.config
  • Use variables
• Duplicate logic in multiple locations
  • Use classes
  • Use functions
• Repeated if-then logic
  • Use loops
• conditionals instead of polymorphism
  • Use strategy pattern
  • Use inheritance
  • Use polymorphism
• Repeated execution patterns
• Lots of duplicate, probably copy-pasted, code
• Only manual tests
  • Unit tests
  • Integration tests
  • Use mock objects
• Static methods everywhere

Summary

• Repetition breeds errors and waste
• Re factor code to remove repetition