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From: <jws...@ra...> - 2004-12-08 13:24:51
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I am using SQLObject with a pre-existing Postgresql database, so I enforce all validation constraints there instead of in the object mapper. I think that's really the most appropriate place to do data validation. Your situation may dictate otherwise, though. >Is it possible to defer the insert/update so that the object can be validated >before the changes are written to the database? |
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From: Peter B. <pet...@14...> - 2004-12-19 21:57:53
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Thanks for all the advice on this, I really appreciate it. I've managed
to get this working by using the code below. You use it like this:
class SomeDomainObject(SQLObject):
...etc
# This will create a new object in the database
form = FormValues(clazz = SomeDomainObject)
form.attr1 = 'value1'
form.attr2 = 'value2'
form.save() #Insert deferred to here
# This will update an existing object
obj = SomeDomainObject.select(...)
form = FormValues(object = obj)
form.attr1 = 'newvalue'
form.attr2 = 'newValue2'
form.save() #Update deferred to here
This code works but I'm not very keen on it because it seems like a hack
to, in particular using "eval" to call the object constructor does not
feel good. Any advice or comments on how to improve this are welcome.
Cheers
Peter
class FormValues:
def __init__(self, clazz = None, object = None):
self.clazz = clazz
self.object = object
def __getattr__(self, attr):
# If we just want the object (as in 'self.object')
if attr == 'object' and self.__dict__.has_key('object'):
return self.__dict__['object']
# Otherwise, if we have an object, pass the call to it
elif self.__dict__.has_key('object') and self.__dict__['object']
is not None:
return getattr(self.__dict__['object'], attr)
# Otherwise return the attr we have (or None if not found)
else:
if self.__dict__.has_key(attr):
return self.__dict__[attr]
else:
return None
def __setattr__(self, attr, val):
# Store the attribute to set it on the object later
self.__dict__[attr] = val
def save(self):
# If we haven't been created with an object, create one
if self.object is None:
initStrings = []
removeAttrs = []
allAttrs = self.__dict__.keys()
for col in self.clazz._SO_columns:
if self.__dict__.has_key(col.name):
initStrings.append('%s = self.%s' % (col.name,
col.name))
allAttrs.remove(col.name)
removeAttrs.append(col.name)
elif col.default is not None and col.default !=
sqlobject.sqlbuilder.NoDefault:
initStrings.append("%s = %s" % (col.name,
`col.default`))
else:
initStrings.append('%s = None' % (col.name))
initString = '%s(%s)' % (self.clazz.__name__,
string.join(initStrings, ','))
self.object = eval(initString)
for attr in removeAttrs:
del self.__dict__[attr]
# Set the attributes that are not columns
for key in allAttrs:
if key != 'object' and key != 'clazz':
setattr(self.object, key, self.__dict__[key])
del self.__dict__[key]
else:
# Otherwise set the values on the object we have
for key in self.__dict__.keys():
if key != 'object' and key != 'clazz':
setattr(self.object, key, self.__dict__[key])
del self.__dict__[key]
> On Thu, 2004-12-09 at 05:51, Ian Bicking wrote:
> > Peter Butler wrote:
> > > I'm just getting to grips with SQLObject so please pardon me if this
> > > is a question that has been asked before.
> > >
> > > Is it possible to defer the insert/update so that the object can be
> > > validated before the changes are written to the database?
> > >
> > > I would like to be able to do the following:
> > >
> > > object = MyObject()
> > > object.field1 = someValue
> > > object.field2 = someValue
> > > object.validate() object.save()
> > >
> > > With similar logic for objects that already exist in the database.
> > >
> > > From looking through the tutorial and source the philosophy seems
> > > to be to write all object changes to the database as they occur.
> > > This makes sense to me as it simplifies everything.
> >
> > You can also set several keys at once using .set(); you might require
> > that the object be valid for each call to .set(). You can also delay
> > saves to the database with _lazyUpdate = True, then you can override the
> > .syncUpdate() method to do validation. Hmm... apparently I haven't
> > included lazyUpdate in the docs, but it is noted in the News.
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From: Oleg B. <ph...@ma...> - 2004-12-20 07:51:18
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On Mon, Dec 20, 2004 at 11:01:49AM +1300, Peter Butler wrote:
> initStrings.append('%s = self.%s' % (col.name,
> col.name))
> allAttrs.remove(col.name)
> removeAttrs.append(col.name)
> elif col.default is not None and col.default !=
> sqlobject.sqlbuilder.NoDefault:
> initStrings.append("%s = %s" % (col.name,
> `col.default`))
> else:
> initStrings.append('%s = None' % (col.name))
> initString = '%s(%s)' % (self.clazz.__name__,
> string.join(initStrings, ','))
> self.object = eval(initString)
Wow! That's a long and a very wrong way of doing things. This is
Python! Do not evaluate strings - just manipulate objects.
args = ["arg1", 2, 3.0]
keywords = {"name1": "valu1", "name2": "value2"}
self.object = self.clazz(*args, **kywords)
Oleg.
--
Oleg Broytmann http://phd.pp.ru/ ph...@ph...
Programmers don't die, they just GOSUB without RETURN.
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From: Peter B. <pet...@14...> - 2004-12-22 02:23:58
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> Wow! That's a long and a very wrong way of doing things. This is > Python! Do not evaluate strings - just manipulate objects. Thanks very much for the advice, I thought there must be a nicer way to do it. I ended up using apply() with the class name and the keyword dictionary. I've put the changed code at http://www.clever.co.nz/FormValues.py if you're interested. I tried _lazyUpdate = True and it does half of what I need (i.e. defers updates to the database until syncUpdate() is called). Is there a similar mechanism for deferring inserts? I hope so, then I can get rid of this ugly code for good! Cheers Peter |
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From: Oleg B. <ph...@ma...> - 2004-12-22 09:13:20
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On Wed, Dec 22, 2004 at 03:27:53PM +1300, Peter Butler wrote:
> Thanks very much for the advice, I thought there must be a nicer way to
> do it. I ended up using apply() with the class name and the keyword
> dictionary.
You only need apply() for very old Python versions. In newer Python
(and SQLObject requires such a new Python) you can just use the
following simple syntax:
args = [...]
keywords = {...}
function(*args, **keywords)
> I tried _lazyUpdate = True and it does half of what I need (i.e. defers
> updates to the database until syncUpdate() is called). Is there a
> similar mechanism for deferring inserts?
There is no, because when you create an object, it have to know its
id, so SQLOBject does INSERT and asks for new id.
Oleg.
--
Oleg Broytmann http://phd.pp.ru/ ph...@ph...
Programmers don't die, they just GOSUB without RETURN.
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From: Charles B. <li...@st...> - 2005-02-04 05:05:45
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The topic of deferring object creation was brought up last December. Thanks
for sharing your solution, Peter. I wanted to see what people thought about
a different (unimplemented) approach.
When dealing with unvalidated data, a temporary object is sufficient, and
the overhead for persisting+removing the object is overkill. Typically I
just create a normal python object for this purpose. However, this approach
requires duplicating definitions of the eventual SQLObject object. (yuk!)
It would be ideal to just use the actual SQLObject itself in this situation,
but without persistence.
I realize that during the initialization of a given SQLObject, the
connection is used to create ids and such, which is why a valid connection
is required.
If there were an in-memory (non-persistent) connection type, maybe something
like the following would be possible:
in_memory_conn = SQLObject.InMemoryConnection()
db_conn = SQLObject.MySQLConnection(....)
temp = SomeSQLObject(connection=in_memory_conn)
... # do some validation actions here
if validation_passed:
persisted = SomeSQLObject(connection=db_conn)
persisted = temp
#or maybe some way to re-assign the connection of the temp object
#and have the object recreated in new connection's database??
#ie temp.save(connection=db_conn) # or resave, or copy, etc
No big deal either way... just wanted to throw the idea out there and see
what people thought. Thanks for all of the cool tools and ideas everyone...
-Charles.
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