Hi Mike,
I'm writing a library that uses SQLAlchemy. The user will pass the library
an update, and the library will add a RETURNING clause for postgresql
users, and then return the model back to the user. The idea here is to
update and select the row in a single database call, instead of the normal
approach where two calls are made.
However, `upd.returning(User)` will actually return a Core row, not the ORM
model instance:
upd = update(User).values(name='foo').where(User.id ==
1).returning(User)
result = session.execute(upd)
row = result.one()
assert isinstance(row, Row)
The key question I have is how to convert a Core row into an ORM model
instance.
`model(**row._mapping)` fails in at least these two cases: different
field name in ORM vs database, and column_property.
I also wonder, should SQLAlchemy return the Model instead of the core row
in this case?
-------
I've gotten this far:
model = model_from_dml(upd)
upd = upd.returning(*select(model).selected_columns) # this will
apply the column_property to the RETURNING
row = session.execute(upd).one()
Now I just need to take this row and convert it to an ORM object.
Is there a public API I can use to take a Core `row` and convert it to an
ORM model?
Thanks and best regards,
Matthew
On Sunday, March 27, 2022 at 11:11:30 AM UTC-7 Mike Bayer wrote:
>
>
> On Sun, Mar 27, 2022, at 2:08 PM, mkmo...@gmail.com wrote:
>
> Hi Mike,
>
> Thanks. Should I use column_descriptions[0]['type'] ?
>
>
> yup, that should be pretty consistent in this case.
>
> I've implemented most of an actual feature for this but isn't committed
> yet at https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/3742
>
>
> In my case, `type`, `expr` and `entity` all return the model class that I
> am interested in.
>
> Thanks and best regards,
>
> Matthew
> On Saturday, March 26, 2022 at 12:02:54 PM UTC-7 Mike Bayer wrote:
>
>
> the Project model is actually in there, but not in a public API place
> (this is not the solution, but look inside of table._annotations to see it).
>
> The closest public API we have for this very new API right now is the
> Query equivalent of column_descriptions, which is available on the select()
> construct and works when the thing being selected is ORM-enabled, and,
> alarmingly, it seems there is no documentation whatsoever for the Select
> version of it, that is wrong, but anyway see the 1.x docs for now:
> https://docs.sqlalchemy.org/en/14/orm/query.html#sqlalchemy.orm.Query.column_descriptions
>
> This accessor would ideally be on insert, update and delete also, which it
> currently is not. However, here's a quick way to get it right now:
>
> class A(Base):
> __tablename__ = 'a'
>
> id = Column(Integer, primary_key=True)
> data = Column(String)
>
>
> upd = update(A)
>
> print(select(upd.table).column_descriptions)
>
> i might take a crack at cleaning this up now but the above will get you
> what you need.
>
> On Sat, Mar 26, 2022, at 1:34 PM, mkmo...@gmail.com wrote:
>
> Hello,
>
> How can I infer the ORM model class from an update (or insert, or delete)
> function result?
>
> upd = update(Project).values(name='foo').where(
> Project.id == 1
> )
>
> def my_library_function(session, upd):
> result = session.execute(upd)
> # how to get the Project ORM model here, using only session and upd ?
>
> I saw that the update() object has a `table` attribute, but this returns
> the Core table (not the ORM model). In addition I don't have access to the
> base/registry from this function (unless it can be derived from session?).
> Moreover it seems like searching the registry is O(n) and will not work in
> all cases, such as when two ORM models map to the same Core table.
>
> Thanks and best regards,
>
> Matthew
>
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
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>
> http://www.sqlalchemy.org/
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http://www.sqlalchemy.org/
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