On Fri, Feb 9, 2018 at 6:45 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'
yes, as mentioned earlier, "values()" is a weird method from earlier days, it produces an iterator directly: for row in query.values(a, b, c): # etc with_entities() is more modern and fits into the usual model where you get a Query you can all all() upon > > 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' OK the confusion here is being aware of what kinds of objects different methods return. The ORM tutorial is a good place to start to get a feel for it. The first() / one() / and all() methods execute the SQL query and return you a result - when you call those, you no longer have a Query object, you've got your data back. The values() method, which doesn't fit into any of this very well, will execute the SQL query and also return you a result, but it returns it as an iterator, but still, when you call it, you no longer have a Query object. If you used the with_entities() method, when you're done calling that, you still have a Query object and you can still do more things with it. > > 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). > The * prefix immediately clicked for my from somewhere else. Maybe > academically from reading about C++.. Something like a pointer to the whole > array. My impression is that yes the "*" was inspired by C notation like you see for printf, but I'm sure the historians would know more about that. Google keeps returning this as the top hit for "python variadic arguments": https://www.saltycrane.com/blog/2008/01/how-to-use-args-and-kwargs-in-python/ > > 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? > > -- > SQLAlchemy - > The Python SQL Toolkit and Object Relational Mapper > > http://www.sqlalchemy.org/ > > To post example code, please provide an MCVE: Minimal, Complete, and > Verifiable Example. 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