Hello,
here is a code example that illustrates how I plan to implement journals
in an accounting application. The attached file models.py contains the
details. I saved it (together with an empty __init__.py) in a new
directory "journals" under django/tests/modeltests of my SVN working
copy (which I just updated to revision 10921), then I went to
django/tests and run the command::
python runtests.py --settings=settings_memory -v1 journals
to test it. I'm almost happy, but I get an unexpected result in line 60::
File "L:\snapshot\django\tests\modeltests\journals\models.py", \
line 60, in modeltests.journals.models
Failed example:
INV.lastnum
Expected:
1
Got:
2
I don't understand why INV.lastnum returns 2 and not 1 at this place. If
you see the reason, then please tell me!
Also, I'd be glad to get feedback on my way of solving this particular
problem, and I suggest to add this to the Django tests collection once I
got it working.
Luc
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"""
Author: Luc Saffre 2009-06-04
A journal is a sequence of numbered documents in accounting applications.
A Journal instance knows the model used for documents in this journal.
A Document instance can look at its journal to find out which subclass
of Document it is.
The journal also manages a counter "lastnum" to control the numbering
of documents.
First we create two journals and some documents::
>>> ORD = Journal(id="ORD",name="Orders",doctype=0)
>>> ORD.save()
>>> INV = Journal(id="INV",name="Invoices",doctype=1,force_sequence=True)
>>> INV.save()
>>> ORD.create_document().save()
>>> INV.create_document().save()
>>> ORD.create_document().save()
>>> ORD.create_document().save()
>>> INV.create_document().save()
>>> for doc in Document.objects.all():
... print unicode(doc)
ORD#1 (1)
INV#1 (2)
ORD#2 (3)
ORD#3 (4)
INV#2 (5)
You can delete any document, leaving a hole in the sequence,
and this number will not be reused.
>>> ORD.lastnum
3
>>> Document.objects.get(pk=1).delete()
Deleting ORD#1 (1)
>>> ORD.lastnum
3
>>> doc = ORD.create_document()
>>> doc.save()
>>> print doc
ORD#4 (6)
For invoices, ``force_sequence=True`` means that it is not allowed to
delete documents in the middle because this would leave a hole in the
sequence::
>>> Document.objects.get(pk=2).delete()
Traceback (most recent call last):
...
DocumentError: INV#1 (2) is not the last document in journal
It's okay to delete the last invoice of a journal.
This will also decrement lastnum so that the number will be reused::
>>> INV.lastnum
2
>>> doc = Document.objects.get(pk=5)
>>> print doc
INV#2 (5)
>>> doc.delete()
Deleting INV#2 (5)
>>> INV.lastnum
1
>>> doc = INV.create_document()
>>> doc.save()
>>> print doc
INV#2 (7)
Here is again the list of documents in the database after these
operations::
>>> for doc in Document.objects.all():
... print unicode(doc)
INV#1 (2)
ORD#2 (3)
ORD#3 (4)
ORD#4 (6)
INV#2 (7)
"""
from django.db import models
class DocumentError(Exception):
pass
DOCTYPE_CLASSES = []
DOCTYPE_CHOICES = []
def register_doctype(cl):
n = len(DOCTYPE_CHOICES)
DOCTYPE_CHOICES.append((n,cl.__name__))
DOCTYPE_CLASSES.append(cl)
class Journal(models.Model):
id = models.CharField(max_length=4,primary_key=True)
name = models.CharField(max_length=100)
doctype = models.IntegerField(choices=DOCTYPE_CHOICES)
lastnum = models.IntegerField(blank=True,null=True,default=0)
force_sequence = models.BooleanField(default=False)
def create_document(self,**kw):
cl = DOCTYPE_CLASSES[self.doctype]
if not kw.has_key('number'):
kw['number'] = self.lastnum + 1
doc = cl(journal=self,**kw)
self.lastnum = kw['number']
self.save()
return doc
def on_delete_document(self,doc):
if doc.number == self.lastnum:
#print "foo", self.lastnum
self.lastnum -= 1
#print "bar", self.lastnum
self.save()
elif self.force_sequence:
raise DocumentError(
"%s is not the last document in journal" % unicode(doc)
)
class Document(models.Model):
number = models.IntegerField()
journal = models.ForeignKey(Journal)
def __unicode__(self):
return "%s#%d (%d)" % (self.journal.id,self.number,self.id)
def delete(self):
self.journal.on_delete_document(self)
print "Deleting", self
return super(Document,self).delete()
class Order(Document):
pass
class Invoice(Document):
pass
register_doctype(Order)
register_doctype(Invoice)
