SQLAlchemy Object Missing when Null is returned

SQLAlchemy Object Missing when Null is returned - Printable Version

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SQLAlchemy Object Missing when Null is returned - Personne - Feb-19-2022

I'm learning Python and SQLAlchemy for the last 2 weeks, I made some progress but I'm having an issue I have no idea how to resolve.

I do have a SQLAlchemy query as:

query = db.session.query(Inventory, BLColor, BLCategory, BLPart, Location). \
        join(BLColor, Inventory.color_id == BLColor.color_id). \
        join(BLCategory, Inventory.category_id == BLCategory.category_id). \
        join(BLPart, Inventory.part_id == BLPart.ITEMID). \
        outerjoin(Location, Inventory.location_id == Location.loc_id,full=False). \
        filter(Inventory.part_id == part_to_find, Inventory.userid == current_user.userid ).order_by(desc(Inventory.quantity))

dbparts = query.all()

Later in my code I assign a variable with the result of this query such as:

 part_form.loc = p.Location.location

So far all works, the problem arises when the location outer join return nothing.

When everything work, when I look at the type and content of the dbparts variable, I see this

dbparts=[(<Inventory 1206>, <BLColor 86>, <BLCategory 26>, <BLPart 3020>, <Location 96>), (<Inventory 1197>, <BLColor 11>, <BLCategory 26>, <BLPart 3020>, <Location 96>), (<Inventory 1201>, <BLColor 10>, <BLCategory 26>, <BLPart 3020>, <Location 96>), (<Inventory 1211>, <BLColor 5>, <BLCategory 26>, <BLPart 3020>, <Location 96>), (<Inventory 1198>, <BLColor 7>, <BLCategory 26>, <BLPart 3020>, <Location 96>), ...

But when the location is blank I see this:

<class 'list'>
dbparts=[(<Inventory 1218>, <BLColor 11>, <BLCategory 479>, <BLPart 30200>, None]

No more <Location ###> !!! Side question how are those <Inventory 1218>, <BLColor 11> , called ?

So when I try to assign

part_form.loc = p.Location.location

Python is errors out with the error message

Error:
 AttributeError: 'NoneType' object has no attribute 'location'

How do I treat this ?

I'd like to do a:
if p.Location.location exist then assign the value of part_form.loc = p.Location.location
but
if p.Location.location does not exist, set the value of part_form.loc = "UNKNOWN"

RE: SQLAlchemy Object Missing when Null is returned - Larz60+ - Feb-19-2022

If you're too far into your project you may not wish to change, but using the ORM version of SQLAlchemy is more straight forward programming wise.

I wrote a tutorial here that will show you the basics with a simple but complete package.

Also take a look at pandas which does a great job for general database operations. See post: https://python-forum.io/thread-36430.html