The main point you should take from Mike's original reply is:
.values() is a weird method and it's pretty old, usually people
just set the columns up front
You probably shouldn't use it.
On Fri, Feb 9, 2018 at 11:45 AM, Jeremy Flowers
<jeremy.g.flow...@gmail.com> wrote:
> Also this didn't work for me:
>
> print(session.query(Jobmst)
> .values(Jobmst.jobmst_type,
> Jobmst.jobmst_name)
> .first()
> )
>
> yields:
> AttributeError: 'generator' object has no attribute 'first'
This is because .first() is a method of Query, but .values() doesn't
return a Query, it returns an iterator (in this case, a generator).
>
> Swapping first to earlier in the chain like so:
>
> print(session.query(Jobmst).first()
> .values(Jobmst.jobmst_type,
> Jobmst.jobmst_name)
> )
>
> yields:
>
>
> AttributeError: 'Jobmst' object has no attribute 'values'
>
This is because Query.first() returns an instance of the thing that
you are querying for (in this case Jobmst).
> I get confused as well, thinking that *columns (from here) infers a list of
> some kind.
>
> So if I don't have a columns variable assigned to a list, I should be able
> to embed one directly with this sort of syntax values([c1,c2])
> But you indicate something like values(c1,c2).
> So that confuses me as a newbie to Python (my background being predominantly
> Java, Groovy, Typescript, Javascript, Angular 2-4, Ionic 2-3).
If your parameters are in a list, you can call a function like this:
params = [1, 2, 3, 4]
function(*params)
# is equivalent to function(1, 2, 3, 4)
I think a similar idea in Javascript is
params = [1, 2, 3, 4]
function.call(null, params)
(my JS is rusty though, so that might be wrong)
> The * prefix immediately clicked for my from somewhere else. Maybe
> academically from reading about C++.. Something like a pointer to the whole
> array.
>
> I've been brushing up on things like *args *kwargs too - so understand their
> purpose.
> Duck typing, passing parameters as a dictionary is known to me from Groovy.
> It still confounds me though knowing what type to pass in the values().
> Have been reading here about it:
>
>
>
>
> On Friday, 9 February 2018 09:48:51 UTC, Jeremy Flowers wrote:
>>
>> I was thinking about this overnight..
>> Do values relates specifically to inserts and updates, not selects/deletes
>> perhaps, which would correlate to SQL syntax.
>> If, it would make sense to indicate that in the documentation
>>
>> On Thursday, 8 February 2018 20:29:45 UTC, Jeremy Flowers wrote:
>>>
>>> I've seen you can do things like this:
>>> fields = ['jobmst_type', 'jobmst_name']
>>> print(session.query(Jobmst).options(load_only(*fields)).first())
>>>
>>> But according to the documentation, you should be able to do something
>>> with Query values() too.
>>> But once again I seem to be dumbfounded by the syntatic sugar.
>>>
>>> What data type does the list of values need?
>>> Is there a way to introspect that ahead of time?
>>>
>>> Thought I was onto something with .base_columns, but that didn't work
>>> either...
>>>
>>> I ended up with something like an instrumentalAttributes mismatch.
>>> print(session.query(Jobmst)
>>> .values([Jobmst.jobmst_type.base_columns,
>>> Jobmst.jobmst_name.base_columns
>>> ])
>>> .first()
>>> )
>>>
>>> sqlalchemy.exc.InvalidRequestError: SQL expression, column, or mapped
>>> entity expected - got '[{Column('jobmst_type', Numeric(scale=0,
>>> asdecimal=False), table=<jobmst>, nullable=False)}, {Column('jobmst_name',
>>> String(length=256), table=<jobmst>, nullable=False)}]'
>>>
>>> BTW: I'm aware of querying with things like query(Jobmst.jobmst_type,
>>> Jobmst.jobmst_name) too - but looking to understand what values expects.
>>> Mike, Can documentation not specify type?
>
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