How to catch exceptions from database calls such as system.db.runPrepUpdate

[Daniel_Webb]

I'm having trouble understanding how to comprehensively catch exceptions thrown while doing database updates. Here is an example where I tried to INSERT a string which could not be converted to a float into a column of type 'float', so obviously it threw an exception. Here is a part of it:

Caused by: org.python.core.PyException: java.lang.Exception: java.lang.Exception: Error executing system.db.runPrepUpdate(INSERT INTO TestTable (val) VALUES (?), [3z], XOM, , false, false)
	... 56 common frames omitted
Caused by: java.lang.Exception: Error executing system.db.runPrepUpdate(INSERT INTO TestTable (val) VALUES (?), [3z], XOM, , false, false)
	... 55 common frames omitted
Caused by: com.inductiveautomation.ignition.client.gateway_interface.GatewayException: SQL error for "INSERT INTO TestTable (val) VALUES (?)": Error converting data type nvarchar to float.

I'm especially interested in the last line since it tells me the real cause, as opposed to the java.lang.Exception, which doesn't tell me WHY the call failed. I wrap a lot of my code in exception catchers, and when I re-raise the exception the GatewayException is stripped out and I don't see it in the re-raised exception. Here's a simplified version of what I'm talking about:

import sys
anInt = '3z'
try:
	system.db.runPrepUpdate("INSERT INTO TestTable (val) VALUES (?)", [anInt], 'XOM')
except:
	errorType,value,trace = sys.exc_info()
	raise errorType, value, trace  # re-raise

which re-raises the java.lang.Exception part (so I see it in the console), but not the GatewayException part. What is the magic import and except clause which will allow me to catch the GatewayException?

[pturmel]

See this topic:

Generic Python error handler?

I’m trying to code a generic type of error handler that I can call from the except clauses from different scripts where the error_handler procedure can take different routes depending on what is passed to it. Ideally, I want a generic error handler that will catch any/all types of errors. My question is, will the str(e) in the except clause below work correctly for all or most types of errors? try: i = 1 / 0 # divide by zero error except Exception as e: error_handler(str(e)) # wil…

[pturmel]

Also, note that java exceptions are allowed to have a "cause" attached, and that one can have a cause, et cetera. Look at e.cause.

[Daniel_Webb]

Thank you!

I knew the trick about catching Java exceptions separately from one of your other replies, but I didn't know about this until your "Generic Python error handler" response.

from java.lang import Throwable

Great advice! It turns out in my example case at the top of the thread, referencing the .cause property of the Java exception provides the exact cause I was looking for:

> print e.cause

com.inductiveautomation.ignition.client.gateway_interface.GatewayException: SQL error for "INSERT INTO TestTable (val) VALUES (?)": Error converting data type nvarchar to float.