[NOTE: ] As Jeremy points out in the notes below, this example really is BAD for web apps because of SQL Injection attacks. You should start looking at PreparedStatements if you have not done so already.
I get to see a lot of code from other developers and it seems that in the past couple of months I’ve seen a LOT of code. Real Studio is a good database programming environment (we can argue all day long about binding but that’s another post) and is arguably very easy to learn and use.
But I can say, without any doubt, that between the code I’ve seen and the questions I’ve answered on the Real Software forums regarding database issues, people just don’t get how to use them. In practically all cases the Real Studio developer could have easily solved their issue if they had just checked the database error bit and the error message.
We see a lot of code that does something like this:
dim rs as recordset = db.sqlselect(s)
while rs.eof = false
//do something with the data
rs.movenext
wend
Pretty straightforward stuff except sometimes the recordset is nil and causes a Nil Object Exception. Nil Object Exceptions are ‘bad’, right? So what do people do? Well, they tend to do something like this:
dim rs as recordset = db.sqlselect(s)
if rs <> nil and rs.recordcount > 0 then
while rs.eof = false
//do something with the data
rs.movenext
wend
end
dim rs as recordset = db.sqlselect(s)
if db.error then
msgbox "DB Error in " + CurrentMethodName + endofline + db.errormessage
return
end
while rs.eof = false
//do something with the data
rs.movenext
wend
I think some of this practice has come from developers migrating from Visual Basic 6 where exceptions are raised on a database error. They expect REALbasic to do it too so don’t even think about it. The other reason is that Real Software’s examples and documentation don’t check for errors like they SHOULD be doing (they might be now that Paul L is doing the documentation but for years this has been a problem).
We do a dozen or so big projects a year so this means that over the past ten years we’ve done hundreds of database projects. Eventually we found ourselves doing the EXACT same code over and over and over and over again and eventually we got tired of it. So we came up with our own methods for checking for and dealing with database errors. One of those is our own SQLSelectRaiseOnError:
dim rs as RecordSet = db.SQLSelect( sql )
if db.Error then
raise new BKS_Database.DatabaseException( db, sql )
end if
return rs
End Function
if db.Error then
ErrorCode = db.ErrorCode
ErrorMessage = db.ErrorMessage
Message = Str( ErrorCode ) + ": " + ErrorMessage
else
ErrorMessage = "Unknown error"
end if
if sql <> "" then
Message = Message + EndOfLine + " " + sql
end if
End Sub
At this point you can guess that we have our versions of SQLSelect, SQLExecute, and DatabaseRecordInsert. Our initial (error handling) method then turns into:
dim rs as recordset = db.sqlselectRaiseOnError(s)
//If exception it returns immediately!
while rs.eof = false
//do something with the data
rs.movenext
wend
So do yourself a favor, always, always, ALWAYS check your database for errors. It will make your life easier – I guarantee it!
If you’ve gotten this far I will say it again:
ALWAYS CHECK YOUR DATABASE FOR ERRORS!
Happy programming! What other tips do you think would help people new to Real Studio?
[Edit: Changed the code calling the new BKS_Database.DatabaseException.]
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