Hello again,
for a while I want to upgrade our application to use SQLAlchemy 0.7.x.
However I am running into changed behaviour wrt.
ClassManager.new_instance. The behaviour I rely on was discussed here:
http://article.gmane.org/gmane.comp.python.sqlalchemy.user/28746
Basically, I want to create an empty instance of a mapped class and
unserialize my data into it. I am not using Pickle because of security
and compatibility fears.
The attached sample program worked fine with SQLAlchemy 0.6.8:
$ python new_instance.py
<__main__.Engineer object at 0x10774d0>
However, with SQLAlchemy 0.7.5 I get
$ python new_instance.py
Traceback (most recent call last):
File "new_instance.py", line 27, in <module>
session.commit()
[...]
File
"/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.7.5dev-py2.6-linux-x86_64.egg/sqlalchemy/engine/default.py",
line 330, in do_execute
cursor.execute(statement, parameters)
sqlalchemy.exc.IntegrityError: (IntegrityError) people.type may not be NULL
u'INSERT INTO people (type) VALUES (?)' (None,)
I'd really like to use 0.7.5 but I don't know how to replace
new_instance. I attached the sample program and a suggested patch for
the documentation: In the declarative example, the type column is
nullable.
I found out the hard way that it should rather not be. Having a
non-nullable type column at least unconvers the problem when writing to
the database, not when reading the corrupted database :-)
Greetings, Torsten
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from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.orm.attributes import manager_of_class
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Person(Base):
__tablename__ = 'people'
id = Column(Integer, primary_key=True)
discriminator = Column('type', String(50), nullable=False)
__mapper_args__ = {'polymorphic_on': discriminator}
class Engineer(Person):
__tablename__ = 'engineers'
__mapper_args__ = {'polymorphic_identity': 'engineer'}
id = Column(Integer, ForeignKey('people.id'), primary_key=True)
primary_language = Column(String(50))
engine = create_engine("sqlite:///")
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
e = manager_of_class(Engineer).new_instance()
session.add(e)
session.commit()
print session.query(Engineer).first()
diff -r ebe9514a69a4 lib/sqlalchemy/ext/declarative.py
--- a/lib/sqlalchemy/ext/declarative.py Sat Jan 28 17:43:13 2012 -0500
+++ b/lib/sqlalchemy/ext/declarative.py Tue Jan 31 12:50:35 2012 +0100
@@ -389,7 +389,7 @@
class Person(Base):
__tablename__ = 'people'
id = Column(Integer, primary_key=True)
- discriminator = Column('type', String(50))
+ discriminator = Column('type', String(50), nullable=False)
__mapper_args__ = {'polymorphic_on': discriminator}
class Engineer(Person):
