I rechecked everything and I realised that the ForeignKey column is case
sensitive. Thanks for your help!
On 29 July 2016 at 17:58, Blair Azzopardi <blai...@gmail.com> wrote:
> Interesting. Yes each table was in a different schema in pre-simplified
> code and I am using SQL server via pyodbc from Linux. I'll try and get a
> more complete test case shortly.
>
> On 29 Jul 2016 5:53 p.m., "Mike Bayer" <mike...@zzzcomputing.com> wrote:
>
>>
>>
>> On 07/29/2016 12:27 PM, bsdz wrote:
>>
>>> Hi
>>>
>>> I'm trying to use DeferredReflection to encapsulate my data model so
>>> that it can easily be instantiated for different environments. However,
>>> I am having trouble creating relationships with a NoForeignKeysError
>>> being raised. I am guessing it is because the table metadata generation
>>> is being deferred, there's not enough information to create the foreign
>>> key information and therefore the relationships.
>>>
>>> I've simplified my code to the following:
>>>
>>> |
>>> importsqlalchemy assa
>>> fromsqlalchemy.orm importsessionmaker,relationship
>>> fromsqlalchemy.ext.declarative importdeclarative_base,DeferredReflection
>>>
>>>
>>> Base=declarative_base(cls=DeferredReflection)
>>>
>>> classCountry(Base):
>>> __tablename__ ='country'
>>>
>>> classUser(Base):
>>> __tablename__ ='user'
>>>
>>> country_id =sa.Column(sa.Integer,sa.ForeignKey('country.country_id'))
>>> country =relationship("Country",uselist=False)
>>>
>>> classMyModel(object):
>>> def__init__(self,env):
>>> self._engine =sa.create_engine("...")
>>> Base.metadata.bind =self._engine
>>> Base.prepare(self._engine)
>>>
>>> defcreate_session_maker(self):
>>> returnsessionmaker(bind=self._engine)
>>>
>>> # This code is run in another module.
>>> mymodel =MyModel("DEV")
>>> Session=model.create_session_maker()
>>> session =Session()
>>> l1 =session.query(User).all()
>>> |
>>>
>>> The following error comes back:
>>>
>>> |
>>> NoForeignKeysError:Couldnotdetermine join condition between parent/child
>>> tables on relationship User.country -there are noforeign keys linking
>>> these tables.Ensurethat referencing columns are associated witha
>>> ForeignKeyorForeignKeyConstraint,orspecify a 'primaryjoin'expression.
>>>
>>
>> can't reproduce. Need information on database in use, and if distinct
>> schemas are involved. See below, and perhaps try to modify this test case
>> in your environment to reproduce your failure.
>>
>>
>> import sqlalchemy as sa
>> from sqlalchemy.orm import sessionmaker, relationship
>> from sqlalchemy.ext.declarative import declarative_base,
>> DeferredReflection
>>
>> e = sa.create_engine("sqlite://", echo=True)
>>
>> e.execute("""
>> create table country (
>> country_id integer primary key
>> )
>> """)
>>
>> e.execute("""
>> create table user (
>> user_id integer primary key,
>> country_id integer,
>> foreign key (country_id) references country(country_id)
>> )
>> """)
>>
>>
>> Base = declarative_base(cls=DeferredReflection)
>>
>>
>> class Country(Base):
>> __tablename__ = 'country'
>>
>>
>> class User(Base):
>> __tablename__ = 'user'
>>
>> country_id = sa.Column(sa.Integer,
>> sa.ForeignKey('country.country_id'))
>> country = relationship("Country", uselist=False)
>>
>>
>> class MyModel(object):
>> def __init__(self, env):
>> self._engine = e
>> Base.metadata.bind = self._engine
>> Base.prepare(self._engine)
>>
>> def create_session_maker(self):
>> return sessionmaker(bind=self._engine)
>>
>> # This code is run in another module.
>> mymodel = MyModel("DEV")
>> Session = mymodel.create_session_maker()
>> session = Session()
>> l1 = session.query(User).all()
>>
>> print(User.country.property.primaryjoin)
>>
>>
>>
>>
>> |
>>>
>>> Any suggestions on how I might get around this?
>>>
>>>
>>> Thanks in advance,
>>> Blair
>>>
>>>
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>>
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>
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