ExecuteReader how to handle NULL?

Question

User-1104215994 posted

Hi,

Is there a practical way to handle NULL and write <g class="gr_ gr_70 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling multiReplace" id="70" data-gr-id="70">lets</g> say "---" instead of NULL for <g class="gr_ gr_94 gr-alert gr_gramm gr_inline_cards gr_run_anim Grammar only-ins replaceWithoutSep" id="94" data-gr-id="94">reader</g>[4<g class="gr_ gr_104 gr-alert gr_gramm gr_inline_cards gr_run_anim Style multiReplace" id="104" data-gr-id="104">] ?</g>

using (var reader = command.ExecuteReader())
                    {
                       

                        while (reader.Read())
                        {
                            

                            if (reader.GetInt32(10) == 0)
                            {
                                status = "Uncertain";
                            }
                            else if (reader.GetInt32(10) == 1)
                            {
                                status = "Confirm";
                            }
                            else
                            {
                                status = "Cancel";
                            }

                            
                            using (StreamWriter outputFile =
                                new StreamWriter(myFullPath, true))
                            {
                                outputFile.WriteLine(
                                    $"{reader[0]};{reader[1]};{reader[2]};{reader[3]};{reader[4]};{reader[5]};{reader[6]};{reader[7]};{reader[8]};{reader[9]}" + ";" +status);
                            }

                            
                        }
                        //No Purchase 
                        if (!reader.HasRows)
                        {
                            using (StreamWriter outputFile =
                                new StreamWriter(myFullPath, false))
                            {
                                
                            }
                        }
                    }

Answer 1

User475983607 posted

Use the null-coalescing operator ??; https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-coalescing-operator

Answer 2

User-1104215994 posted

can you elaborate please?

Answer 3

User475983607 posted

can you elaborate please?

Sure, click the link in my first post and read. Write code based on the null-coalescing operator and test.  If you run into trouble share your code.

{reader[1] as string ?? "---" }

{reader[0] as int? ?? default}

There's also static and extension methods which you'll need to implement if you are trying to convert data types; int -> string.  This is basic logic for a developer with your experience, IMHO.

Answer 4

User665608656 posted

Hi cenk,

According to your description, I recommend you can use IsDBNull to determine ExecuteReader whether it is null.

For more details, you could refer to following code:

   string res4 = string.Empty;
   if (!reader.IsDBNull(4))
       res4 = reader.GetString(4);
   else
       res4 = "---";
   outputFile.WriteLine(
     $"{reader[0]};{reader[1]};{reader[2]};{reader[3]};{res4};{reader[5]};{reader[6]};{reader[7]};{reader[8]};{reader[9]}" + ";" +status);

Best Regards,

YongQing.