On 6/25/14, 7:11 AM, Tara Andrews wrote:
> Hello,
>
> I am trying to use SQLAlchemy to map a database that was made
> available to me, whose contents and schema cannot be altered. The
> database has a few cases where a many-to-one relationship is treated
> as a many-to-many - that is, instead of the child key being set
> directly onto the parent record, the relationship is mapped through an
> association table. So in the mapping it looks like this:
>
> vname_association = Table('VNameFactoid', Base.metadata,
> Column('vnameKey', Integer, ForeignKey('VariantName.vnameKey')),
> Column('factoidKey', Integer, ForeignKey('Factoid.factoidKey')))
>
> class Factoid(Base):
> __tablename__ = 'Factoid'
> tstamp = Column(Time)
> engDesc = Column(Text)
> origLDesc = Column(Text)
> factoidKey = Column(Integer, primary_key=True)
> vnameInfo = relationship("VariantName",
> secondary=vname_association, backref="factoidData")
>
> class VariantName(Base):
> __tablename__ = 'VariantName'
> tstamp = Column(Time)
> vnameKey = Column(Integer, primary_key=True)
> name = Column(String)
>
>
> This means that I can get at the variant name information from the
> factoid by saying
> my_variant_name = some_factoid.vnameInfo[0].name
>
> But it would be much nicer if I could dispense with that [0], since I
> know that there will never be more than one record returned in the
> list. Is there something I can do to be able to say this?
> my_variant_name = some_factoid.vnameInfo.name
yes you can apply the "uselist=False" option to the relationship. If
the relationship loads more than one row you'll get a warning.
>
> Best,
> -tara
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