Interestingly I've just discovered the concept of Bundles. http://docs.sqlalchemy.org/en/latest/orm/loading_columns.html#column-bundles
Im guessing this could be used to have it populate the model instance with the extra columns ? On Thursday, 15 June 2017 13:25:00 UTC+1, mike waites wrote: > > Hi > > This is something i've been wrestling in different ways for some time so i > thought it was time that i sought a definitive answer on what the "proper" > way to do this is with the ORM. > > Often you'll want to have some kind of scalar sub select that computes a > column in your query. This can be achieved easily by doing the following > > session.query(Model,scalar_sub_query).filter(...) > > When passing additional column properties to the Query constructor like > this results in SQLAlchemy giving you a named tuple back. In some cases > this is fine but notice the first argument passed was Model, this is > because we also want the ORM to do its normal thing of populating an > instance of Model for us from the result of the query. > > In some cases this can be worked around by using declared_attr. This will > allow us to define a field that is configured at import time from a > function or something like that. This, in my experience, is suitable in > rare occasions. The moment you need something that is not setup at import > time makes this unsuitable. IE suppose your column requires a user id to > figure out the result. > > The next thing that comes to mind is hybrid_property. This is a lot > closer to what we want in most cases, the function is deferred until query > time however, to my knowledge there's no way to have SQLAlchemy > automatically populate a Model instance property from a hybrid_property > which result in use coming back to the original problem. Specifying columns > explicitly results in a named tuple when we simply want our model instance > populated. > > There's no doubt a way to do this but i've given up trying to find it. > > Hope someone can help! > -- 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. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
