[sqlalchemy] Re: How to define a column as read-only (e.g. computed by column in Firebird)

2007-11-08 Thread Werner F. Bruhin 

Mike,

Michael Bayer wrote:
 ...
 oh sorry, I misread the source code in SA earlier...for an INSERT, we  
 are going to insert None for all columns that are blank but dont  
 have a default.  so your two options here are to put another  
 PassiveDefault on the column:

 Column(u'consumedvalue',  
 Numeric(precision=18,length=2,asdecimal=True), PassiveDefault()),
   
That did the trick.

Thanks a lot
Werner

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[sqlalchemy] Re: How to define a column as read-only (e.g. computed by column in Firebird)

2007-11-07 Thread Werner F. Bruhin 

Mike,

Michael Bayer wrote:
 On Nov 7, 2007, at 12:32 PM, Werner F. Bruhin wrote:

   
 Can you point out what I did wrong, please.

 

 id have to see a larger example, seems like something is marking the  
 column as modified when it should not be.
   
I put a little test case together, which does very little but I get the 
exception.

engine = sa.create_engine(url, encoding='utf8', echo=True)
Session = sao.sessionmaker(autoflush=True, transactional=True)
Session.configure(bind=engine)
session = Session()

dbItemConsumption = db.Consumption()
dbItemConsumption.fk_cbbottleid = 33
session.save(dbItemConsumption)

session.flush
session.commit()

Here the echo output and the exception is:
2007-11-07 18:52:53,438 INFO sqlalchemy.engine.base.Engine.0x..d0 BEGIN
2007-11-07 18:52:53,460 INFO sqlalchemy.engine.base.Engine.0x..d0 SELECT 
gen_id(gen_consumption_consumptionid, 1) FROM rdb$database
2007-11-07 18:52:53,460 INFO sqlalchemy.engine.base.Engine.0x..d0 None
2007-11-07 18:52:53,463 INFO sqlalchemy.engine.base.Engine.0x..d0 INSERT 
INTO consumption (consumptionid, quantity, unitprice, consumedvalue, 
remarks, consumed, maturityfirst, maturitybest, maturitypast, created, 
updated, fk_reasonid, fk_cbbottleid, transferid, fk_cellarid, 
fk_ratingid) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
2007-11-07 18:52:53,464 INFO sqlalchemy.engine.base.Engine.0x..d0 [58, 
None, None, None, None, None, None, None, None, None, None, None, 33, 
None, None, None]
2007-11-07 18:52:53,466 INFO sqlalchemy.engine.base.Engine.0x..d0 ROLLBACK

Traceback (most recent call last):
  File saTest.py, line 27, in module
session.commit()
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\session.py,
 
line 483, in commit
self.transaction = self.transaction.commit()
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\session.py,
 
line 210, in commit
self.session.flush()
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\session.py,
 
line 681, in flush
self.uow.flush(self, objects)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 216, in flush
flush_context.execute()
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 432, in execute
UOWExecutor().execute(self, head)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1051, in execute
self.execute_save_steps(trans, task)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1070, in execute_save_steps
self.execute_childtasks(trans, task, False)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1088, in execute_childtasks
self.execute(trans, child, isdelete)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1051, in execute
self.execute_save_steps(trans, task)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1070, in execute_save_steps
self.execute_childtasks(trans, task, False)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1088, in execute_childtasks
self.execute(trans, child, isdelete)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1051, in execute
self.execute_save_steps(trans, task)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1070, in execute_save_steps
self.execute_childtasks(trans, task, False)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1088, in execute_childtasks
self.execute(trans, child, isdelete)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1051, in execute
self.execute_save_steps(trans, task)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1070, in execute_save_steps
self.execute_childtasks(trans, task, False)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1088, in execute_childtasks
self.execute(trans, child, isdelete)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1051, in execute
self.execute_save_steps(trans, task)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1070, in execute_save_steps
self.execute_childtasks(trans, task, False)
  File 
c:\python25\lib\site-packages\SQLAlchemy-0.4.0-py2.5.egg\sqlalchemy\orm\unitofwork.py,
 
line 1088, in execute_childtasks
self.execute(trans, child, isdelete)
  File

[sqlalchemy] Re: How to define a column as read-only (e.g. computed by column in Firebird)

2007-11-07 Thread Michael Bayer 


On Nov 7, 2007, at 10:23 AM, Werner F. Bruhin wrote:


 How can I define a column in the table as read-only?

 I have some computed by columns, e.g.:
 consumedvalue  computed by (quantity*unitprice)

 These columns can not be updated, otherwise I get the following  
 exception:
 ProgrammingError: (ProgrammingError) (-151, 'isc_dsql_prepare: \n
 attempted update of read-only column')


read-only behavior is a class-level thing, so something like this:

class MyClass(object):
 def mycol(self):
 return self._mycol
 mycol = property(mycol)

mapper(MyClass, mytable, properties={
'_mycol':mytable.c.mycol,
'mycol':synonym('_mycol')
})


Theres a ticket in trac which will make the above configuration  
slightly less verbose in a future release.

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[sqlalchemy] Re: How to define a column as read-only (e.g. computed by column in Firebird)

2007-11-07 Thread Michael Bayer 


On Nov 7, 2007, at 12:58 PM, Werner F. Bruhin wrote:


 Mike,

 Michael Bayer wrote:
 On Nov 7, 2007, at 12:32 PM, Werner F. Bruhin wrote:


 Can you point out what I did wrong, please.



 id have to see a larger example, seems like something is marking the
 column as modified when it should not be.

 I put a little test case together, which does very little but I get  
 the
 exception.


oh sorry, I misread the source code in SA earlier...for an INSERT, we  
are going to insert None for all columns that are blank but dont  
have a default.  so your two options here are to put another  
PassiveDefault on the column:

Column(u'consumedvalue',  
Numeric(precision=18,length=2,asdecimal=True), PassiveDefault()),

or you can leave the column out of the mapping entirely (but then  
reading it requires an extra query):

   mapper(Consumption, consumption_table,  
exclude_properties=['consumedvalue'])

the consumedvalue column will post-fetch after an INSERT statement.


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[sqlalchemy] Re: How to define a column as read-only (e.g. computed by column in Firebird)

2007-11-07 Thread Michael Bayer 


On Nov 7, 2007, at 12:32 PM, Werner F. Bruhin wrote:



 Can you point out what I did wrong, please.


id have to see a larger example, seems like something is marking the  
column as modified when it should not be.

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[sqlalchemy] Re: How to define a column as read-only (e.g. computed by column in Firebird)

2007-11-07 Thread Werner F. Bruhin 

Mike,

Michael Bayer wrote:
 On Nov 7, 2007, at 10:23 AM, Werner F. Bruhin wrote:

   
 How can I define a column in the table as read-only?

 I have some computed by columns, e.g.:
 consumedvalue  computed by (quantity*unitprice)

 These columns can not be updated, otherwise I get the following  
 exception:
 ProgrammingError: (ProgrammingError) (-151, 'isc_dsql_prepare: \n
 attempted update of read-only column')

 

 read-only behavior is a class-level thing, so something like this:

 class MyClass(object):
  def mycol(self):
  return self._mycol
  mycol = property(mycol)

 mapper(MyClass, mytable, properties={
 '_mycol':mytable.c.mycol,
 'mycol':synonym('_mycol')
 })


 Theres a ticket in trac which will make the above configuration  
 slightly less verbose in a future release.
   
I don't have many of these, so no big deal that it is verbose.

However I must not do something wrong in transposing the above as I 
still get the error.

I must be a bit dense on this, here is what I have done:

consumption_table = sa.Table(u'consumption', metadata,
sa.Column(u'consumptionid', sa.Integer(), 
sa.Sequence('gen_consumption_consumptionid'), primary_key=True, 
nullable=False),
sa.Column(u'quantity', sa.Integer()),
sa.Column(u'unitprice', 
sa.Numeric(precision=18,length=2,asdecimal=True)),
sa.Column(u'consumedvalue', 
sa.Numeric(precision=18,length=2,asdecimal=True)),

)

class Consumption(object):
def consumedvalue(self):
return self._consumedvalue
consumedvalue = property(consumedvalue)
pass

consumption = sao.mapper(Consumption, consumption_table,
properties={
...
'cellar': sao.relation(Cellar, backref='consumption'),
'_consumedvalue': consumption_table.c.consumedvalue,
'consumedvalue': sao.synonym('_consumedvalue'),
})

Can you point out what I did wrong, please.

Werner

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