Question

I’m trying to convert a one-to-many part of a many-to-many relationship to a python set(). See the following play example for code:

message_tos = Table('message_tos', Base.metadata,                                
    Column('message_id', Integer, ForeignKey('message.id')), 
    Column('address_id', Integer, ForeignKey('address.id'))
)

class Address(Base):
    address = Column(String, nullable=False, unique=True)
    emails = relationship('Message')

    def __init__(self, address):
        self.address = address

class Email(Base):
    from = relationship('Address', backref='from')
    to = relationship('Address', secondary=message_tos, backref='messages_to')
    message_id = Column(String, nullable=False, unique=True)

...

def whatever(*args, **kwargs):
    """
        ...
    """
    email = session.query(Email).filter(Email.message_id==message_id).first()
    blah = set(email.to).union(email.from) # This lines throws an error that Address is not iterable

Is there any way to run the set(email.to) code (which places an Address object into a set), or am I going about this completely the wrong way? Obviously, I could just do set([email.to]), however this is an entire extra order of complexity (and this function may be called multiple times with potentially very long .to or .from lists) which I’d rather not have

Answer 1

Your error most probably occurs not in the set(email.to) part, but in .union(email.from), since the email.from is not iterable. According to your code, email.from is an instance of Address.

This should work though: blah = set(email.to).union([email.from]). I assume that did not really call the property from, as it is a reserved keyword in python. I guess sender is a good name.

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Also note that in SA searching for a primary key can be done clearer with the Query.get:

email = session.query(Email).get(message_id)