When to call DB Errorhandling-Method?

Databases
1

Hi,

i use several database-methods with SQLite and MySQL. I also use a DBError-Method to catch the errors and to display a message to the user. This works almost fine, but i want to be sure:

where is the right place to call a db-error-method?

After which db-commands should my app check for an DBError?

Michael

2

every :slight_smile:

3

At least SQLSelect, SQLExecute and Prepare to catch the SQL syntax errors.

4

Hi Christian,

with “every” you mean every db-command in xojo? i don’t think so. Let take this code:


  dim dbFile as FolderItem
  
  dbFile = GetFolderItem("database").Child("database.sqlite")
  
  if dbFile <> Nil then
    
    SQLiteDB = new SQLiteDatabase
    SQLiteDB.DatabaseFile = dbFile
    
    if SQLiteDB.Connect then
      return
    else
      MsgBox("Datenbankfehler: " + SQLiteDB.ErrorMessage)
    end if
    
  end if

dim sql as String = "SELECT * FROM kunden ORDER BY firma COLLATE NOCASE"
    
    dim rs as RecordSet = SQLiteDB.SQLSelect(sql)
    
    while not rs.EOF
      Listbox1.AddRow
      Listbox1.RowTag(Listbox1.LastIndex) = rs.Field("ID").IntegerValue
      Listbox1.Cell(Listbox1.LastIndex, 0) = rs.Field("nummer").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 1) = rs.Field("firma").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 2) = rs.Field("telefon").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 3) = rs.Field("telefax").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 4) = rs.Field("email").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 5) = rs.Field("strasse").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 6) = rs.Field("hausnummer").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 7) = rs.Field("postleitzahl").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 8) = rs.Field("standort").StringValue
      Listbox1.Cell(Listbox1.LastIndex, 9) = rs.Field("land").StringValue
      rs.MoveNext
    wend
    
    if DBError then return
    
    rs.Close

After which commands you would place a “if DBError then return” which calls the Errorhandling-Method and returns True or False?

Michael

5

well, in your code, you need to put it at least after the SQLiteDB.SQLSelect.
rs could be nil. If one of the fields does not exist, you get a NilOBjectException there.

Personally I don’t use the close command there and let the recordset go out of scope.

Technically even the EOF or MoveNext could cause an error…

6

Thank you, Christian.

Michael