Thank you for your support and contributions, Mike, you are a great person.
понедельник, 12 февраля 2018 г., 13:14:24 UTC+3 пользователь Stanislav
Lobanov написал:
>
> Hello, i'm supporting legacy database, and using such models (code
> contains examples of my problem, keep reading):
>
> class Product: # This table is never used straightforward in queries
>
> type = Column(db.Integer)
> name = Column(db.String)
>
> TYPE_GUITARS = 1
> TYPE_DRUMS = 2
>
> __tablename__ = 'product'
> __mapper_args__ = {
> 'polymorphic_on': type,
> }
>
>
> class Guitars(Product):
> __mapper_args__ = {
> 'polymorphic_identity': Product.TYPE_GUITARS, # Guitars entity
> }
>
>
> class Drums(Product):
> __mapper_args__ = {
> 'polymorphic_identity': Product.TYPE_DRUMS, # Drums entity
> }
>
>
> # This query returns nothing.
>
> query1 = session.query(Musician).filter(
> Musician.guitar == Guitars.id,
> Musician.drum == Drums.id,
> )
>
> # Because SQL query built is wrong:
>
> # select * ... *from product* where ... => no rows returned
>
> # To fix his i use aliased() function:
>
> guitars = aliased(Guitars, name='guitars')
> drums = aliased(Drums, name='drums')
>
> query2 = session.query(Musician).filter(
> Musician.guitar == guitars.id,
> Musician.drum == drums.id,
> )
>
> # select * ... *from product as guitars, product as drums* where ... =>
> working fine
>
>
>
> My problem is that when i'm using two Polymorphic Models (with one
> database table) i always must use aliased() function. This is demonstrated
> in example higher.
>
> As you can see, query1 produces no results, because it is selecting from
> *products* table, and applies two filters to it. Instead it should use *two
> product table aliases. *It can be achieved with using *aliased()*
> function.
>
> So, finally, my question is:
>
> Are there any mechanism in sqlalchemy that can automatically apply aliases
> to such tables, if it sees their combination in query?
>
>
--
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.
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