Error Handling

Error handling

Error reporting in SQL Yoga is of two types:

1. Handlers that throw errors
2. Handlers that return errors in the result

Handlers that throw errors

SQL Yoga will handlers will throw errors if the error is a development error or if it is a database connection error. A development error means that the error is caused because you have misconfigured something or are trying to use the API incorrectly.

Here is a list of error numbers that are thrown and the | used in SQL Yoga which describes the erorr. The error number is the number used by LiveCode to report specific errors.

Error Number	Description
422	kErrInvalidArray
452	kErrInvalidBoolean
453	kErrInvalidNumber
456	kErrPropDoesntExist
354	kErrInvalidInteger
355	kErrInvalidPoint
356	kErrInvalidRect
449	kErrReadOnlyProp
348	kErrInvalidProperty
619	kErrCantFindObject
487	kErrRenameErrorInDestination
132	kErrObjectNameTaken
238	kErrInvalidGroupObject
219	kErrErrorInFunction

In addition to the general LiveCode errors above, SQL Yoga will also throw errors specific to SQL Yoga. Errors have one of the following prefixes, followed by a ,, followed by the specific error message.

Error Prefix	Description
sqlyoga_connection_err	An error occurred while trying to connect to the database.
sqlyoga_executesql_err	An error occurred while trying to execute a SQL statement.

Handling thrown errors

There are two ways to handle errors that are thrown. The first is to wrap all calls to handlers that execute SQL statements or connect to the database with a try/catch statement:

try
  dbconn_connect
catch e
  answer "An error occurred while connecting to the database:" && e
end try

Another approach is to define your own errorDialog handler somewhere in the message path (e.g. a library script). When your app is running in the IDE you can pass the errorDialog message and allow the IDE to report the error to you using the standard error reporter.

When your app is running as a standalone you can define how you want to respond to errors at a global level. For example, if the database connection is invalid and a sqlyoga_connection_err error is thrown then you might want to display a dialog that allows them to update the connection settings.

# Card script
on openCard
  # No try/catch arround handler that can throw an error
  ...
  dbconn_connect
  ...
end openCard

# library script
on errorDialog pError
  # Let the IDE display the error in development
  if the environment is "development" then pass errorDialog

  switch item 1 of pError 
    case "sqlyoga_connection_err"
      # handle connection error here
      break
  end switch
end errorDialog