Mike Orr wrote:
> Is it possible to make a mapper class that loads & modifies only some
> fields in a table rather than all the fields, yet still autoloads the
> fields rather than having hardcoded column types? I've been avoiding
> the ORM because frequenty I want to iterate every record without
> loading some large text fields, and to avoid 20-line SELECTS in the
> log which make debugging less convenient. Yet now I have a
> data-conversion project and have been charmed at the ability to load
> an object, modify and flush it, without having to do "SELECT" +
> "UPDATE ... WHERE"
If this is a batch type process you are undertaking and will be doing
repeatedly, don't succumb to the temptation of using ORM. Your
performance will suffer. Especially if you are doing things like auto
inserting parent - child objects with auto increment keys in the child.
I did a recent batch import script using SA ORM and although it worked
perfectly, the performance was lacking. This of course is not SA's fault
but it was just a case of choosing the right tool for the right job. It
was a breeze to change all my ORM code to using SA sql though, so it
wasn't a big deal. I used a convenience method to create my insert
statements so it was almost like my ORM code. so instead of
session.save(obj), I had:
def get_columns(table, o):
result = {}
for c in table.c:
if hasattr(o, c.name):
val = getattr(o, c.name)
if val is not None:
result[c.name] = val
return result
my_table.insert().execute(**get_columns(my_table, my_object))
The ORM is misleadingly simple (especially if you go berzerk with
relations). Because I tend to go berzerk with joins, it's straight SA
SQL all the way for me. For batch stuff, it was a killer when SA
pre-fetched all the database default values. eg. "select
local_timestamp()", "select nextval('')" for every single row.
Huy
SA.Fan
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