Company has an address_id column, which means each company only has a
single address, doesn't it? ie. this is a many-to-one relationship,
not a many-to-many?
Simon
On Mon, Jan 27, 2020 at 11:28 PM Radek Krzak <radek.kr...@gmail.com> wrote:
>
> Hello,
>
> I have a ManyToMany relationship between two tables, although I am not using
> "foreign keys" to establish it (this is a deliberate decision that I wouldn't
> like to explain more at this point). However, I am struggling to define this
> relationship using SQLAlchemy. At the very beginning, I found the primaryjoin
> that I tried using with partial success. I managed to get it working with
> backref (and with only one side being a list, which is not what I wanted),
> but to be honest it was rather by accident. I keep missing the
> information/examples of how exactly the foreign_keys and remote_side
> arguments are and how to use them effectively. I went through every single SO
> question on that topic and the documentation that mainly involves self joins
> (that is understandable as my use case is rather uncommon).
>
>
> class Address(Base):
> __tablename__ = 'addresses'
> id = Column(UUID, primary_key=True)
> address_id = Column(String(8), nullable=False)
> is_deleted = Column(Boolean, server_default=expression.false(),
> nullable=False)
> companies = relationship("Company", primaryjoin="...",
> back_populates="addresses")
>
>
> class Company(Base):
> __tablename__ = 'companies'
> id = Column(UUID, primary_key=True)
> address_id = Column(String(8), nullable=False)
> addresses = relationship("Address", primaryjoin="...",
> back_populates="companies")
>
>
> I would like a bidirectional relationship with using back_populates (I don't
> like using backref as my models are often scattered across different modules
> and I prefer to be explicit). I am not using primary keys on purpose as I
> want to keep the historical addresses data just by marking address by deleted
> (and keeping companies and address linked via address_id). Referential
> integrity is enforced by the 3rd party provider where I import the data from,
> so this is not an issue in my case.
>
> Any help on how I should define the relationship on both models is
> appreciated. I really want to understand foreign_keys and remote_side because
> at the moment I cannot seem to be able to wrap my head around, even after
> reading
> https://docs.sqlalchemy.org/en/13/orm/join_conditions.html#creating-custom-foreign-conditions
> :(
>
> Thanks in advance
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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