You're best starting with the declarative usage patterns described in the ORM
tutorial at http://www.sqlalchemy.org/docs/orm/tutorial.html, starting with
http://www.sqlalchemy.org/docs/orm/tutorial.html#creating-table-class-and-mapper-all-at-once-declaratively.
I would declare the class + table + mapping at once, to eliminate any
confusion regarding mapping, which is not a per-usage operation; it is a
permanent operation applied to a model class only once. The mapper() +
Table pattern is not as easy to use and it's being de-emphasized in the
documentation.
The second error implies your class has a method called value() on it which is
conflicting with the mapped attribute of .value.
On Jun 14, 2011, at 12:22 PM, Liju wrote:
I'm new to SQLAlchemy. I wrote a method that retrieves a record,
update the object after incrementing it by 1, and return that record
object to the caller (pyramid view). Following is the test function. I
get following errors :
1) when I call this method multiple times, I get an error that say
ArgumentError: Class 'class 'cas.models.Models'' already has a
primary mapper defined. Use non_primary=True to create a non primary
Mapper. clear_mappers() will remove *all* current mappers from all
classes.
As a resolution i called 'clear_mappers()' before invoking mapper.
2) I cant seem to increment the attribute of an object in orm session.
My understanding is that once a record is retrieved in an ORM session,
Session object keeps track of any changes to the record object and
updates the record when session.flush() is invoked.
But I get error TypeError: unsupported operand type(s) for +:
'instancemethod' and 'int'
Can someone please explain to me what I'm doing wrong ?
class Models(object):pass
def countAndIncrement():
metadata = MetaData('sqlite:///CAS.db')
model_table = Table('models',
metadata,
Column('id',Integer,primary_key=True),
Column('name',String(40)),
Column('value',Integer)
)
clear_mappers()
mapper(Models,model_table) # already a
primary mapper defined error (when I call this function multiple times
Session = sessionmaker()
session = Session()
model = session.query(Models).filter(Models.id==1)
model.value = model.value + 1 #
increment error
session.flush()
session.close()
return model
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