ODBC return values from iSeries on Linux

Question

This is using pyodbc.

Okay, let's say I create a procedure on the iSeries using something like this:

CREATE PROCEDURE MYLIB.MYSQL(IN WCCOD CHAR ( 6), INOUT WPLIN CHAR (3))
RESULT SETS 1 LANGUAGE CL NOT DETERMINISTIC   
CONTAINS SQL EXTERNAL NAME MYLIB.MYCL PARAMETER STYLE GENERAL

Then in Python I do something like this:

cust = 'ABCDEF'
line = '123'
sql = "CALL MYLIB.MYSQL('%(cust)s',?)" % vars()
values = (line)
c = pyodbc.connect('DSN='+system+';CMT=0;NAM=0')
cursor = c.cursor()
cursor.execute(sql,values)

Nothing in the variables shows the return value. The sense I get from seeing comparable code in other languages (ie. .NET) is that the ODBC "variable" is defined, then updated with the return value, but in this case neither "line" or "values" is changed.

I realize one alternative is to have the CL program write the result to a file then read the file, but it seems like an extra step that requires maintenance, never mind added complexity.

Has anyone ever made this work?

Answer 1

Holy cow, I got it working, but it takes two procedures, one to call the CL one to run the SQL statement.

For example (first procedure, this is what calls the CL program that returns a value in WPLIN):

CREATE PROCEDURE MYLIB.MYSQLA(IN WCCOD CHAR ( 6), INOUT WPLIN CHAR (3))
RESULT SETS 1 LANGUAGE CL NOT DETERMINISTIC   
CONTAINS SQL EXTERNAL NAME MYLIB.MYCL PARAMETER STYLE GENERAL

Second procedure (will call the first, THIS is the procedure we call from ODBC):

CREATE PROCEDURE MYLIB.MYSQLB(IN WCCOD CHAR ( 6), INOUT WPLIN CHAR (3))
DYNAMIC RESULT SETS 1 LANGUAGE SQL 
BEGIN
DECLARE C1 CURSOR WITH RETURN TO CLIENT
FOR 
SELECT WPLIN FROM DUMMYLIB.DUMMYFILE;
CALL MYLIB.MYSQLA(WCCOD,WPLIN);
OPEN C1;
END

Then from an ODBC connection, we simply execute this:

customer = 'ABCDEF'
line='ABC'
sql = "{CALL MYLIB.MYSQLB('%(customer)s','%(line)s')}" % vars()
cursor.execute(sql)
print cursor.fetchone()

Et voila!

A caveat: The "DUMMYLIB/DUMMYFILE" are a single record physical file I created with a single byte column. It's only used for reference (unless there's a better way?) and it doesn't matter what's in it.

Maybe a bit clumsy, but it works! If anyone knows a way to combine these into a single procedure that would nice!

Answer 2

First, you won't get any results at all if you don't fetch them. When using pyODBC (or practically any other package adhering to Python Database API Specification v2.0), you have a couple of choices to do this. You can explicitly call one of the fetch methods, such as

results = cursor.fetchall()

after which the result set will be in results (where each result is a tuple and results is a list of these tuples). Or you can iterate directly over the cursor (which is a bit like repeatedly calling the .fetchone() method):

for row in cursor:
    # Do stuff with row here
    # Each time through the loop gets another row
    # When there are no more results, the loop ends

Now, whether you explicitly fetch or you use Python's looping mechanism, you receive a brand-new collection of values, accessed by the names you chose to receive them (results in my first example, row in my second.) You can't specify Python variables to be updated directly by individual values.

Besides the Python DB API 2.0 spec mentioned above, you'll probably want to read up on pyODBC features, and particularly on the way it handles stored procedures.