I'm still confused about what you have (what form of inheritance you are using.
In your database, are there both a Word table and a Verb table? Or is there just a (set of) Verb (and Noun and Adjective, etc.) table(s), derived from a non-Model Word class? If there's a Noun instance "record" and a Verb instance "record", do they share any data (such that if you change it in one it is changed in the other) or do they just have duplicate copies of some data? Bill On Thu, Jun 23, 2011 at 11:36 AM, Matthew Gardner <mj...@byu.edu> wrote: > Thanks, Bill, for your comments. > Shortly after I posted here I did a little more digging and found this > thread from six months ago that described exactly my problem: > http://groups.google.com/group/django-users/browse_thread/thread/9400999651577bc2/8cc4fe267128d6a3 > That thread didn't seem to have a good solution, though... > As far as whether I should have done inheritance or composition, that's a > fair question that could have gone either way. But I chose inheritance a > while ago, as it seemed to make the most sense for what I am doing, and > that's the way the code is written. At several points in my code, I have > blocks that do things like this: > try: > verb = word.verb > # do verb-specific stuff > except Verb.DoesNotExist: > pass > I deal with a collection of words most of the time, and if they are also > verbs I add some additional stuff. > At this point, all I really want to do is add a row to the verb table that > contains the correct foreign key, without creating a new row in the word > table. And I don't want to write SQL to do it, though if I don't find > another solution, that's what I'm going to do, because it's fairly > straightforward to just do that. Also, I want to be able to delete just the > verb part, which is just deleting the row in the verb table and all > corresponding information (i.e., some other tables reference verb but not > word, so on deleting the verb row you want to delete the references to it). > And, now that I look at this, it seems that composition would have > simplified those two things, as django makes that nice and easy (with a > one-to-one field in Verb). If I can figure out a nice way to do it while > keeping inheritance, it would make my life easier, as I already have a bunch > of code written and databases that I don't want to repair that use > inheritance. But, given that it looks like composition would probably be > easier, maybe I should just take the hit and convert everything? Thoughts? > On Thu, Jun 23, 2011 at 10:09 AM, Bill Freeman <ke1g...@gmail.com> wrote: >> >> First, if, despite being related by inheritance, Word and Verb are >> separate models, they have separate tables. Then if you do create >> a Verb, the Word still exists, unless you delete it. Is that what you >> want? If both are to exist, were you hoping that a query for the >> same key would still find the Word, or do you want it to find the Verb. >> And how do you want to treat words (if text words they are) like "record", >> which is a noun (keep a record), a verb (record a performance) and an >> adjective (record crowd), at the very least. (Note that the pronunciation >> of the verb is different, if you were thinking of storing pronunciation >> info >> in the Word.) >> >> If you have separate models, you could certainly write the method that >> initializes a completely separate sub-class instance from the instance >> data of the super class instance. You could also do some magic using >> the field list available in the manager (which has the problem, IIRC, that >> it is not a public interface) to know which data to copy, though I'm of >> the >> explicit is better than implicit camp. >> >> So, I guess that I really don't know enough about your problem to >> suggest a detailed technique. I suspect that if it were me, I'd probably >> be using a foreign key reference from Verb to Word, rather than >> sub-classing. >> >> Bill >> >> On Wed, Jun 22, 2011 at 9:45 PM, Matt Gardner <drai...@gmail.com> wrote: >> > Hello all, >> > >> > I have a model hierarchy in my django app, and there is one very >> > important task that I do not know how to do. I have a bunch of >> > instances of the superclass (Word is the model name), and on input >> > from a user I want to create a subclass instance (Verb) from that >> > superclass instance. For example, I might have code like this: >> > >> >>>> word = Word.objects.get(pk=[input from user]) >> >>>> verb = Verb.createFromSuperclassInstance(word) >> >>>> verb.save() >> > >> > The only problem is that I know of no such >> > "createFromSuperclassInstance" method, nor where to look for it. I do >> > know how to do this through the database itself (just add a row to the >> > verb table with the correct foreign key), but I was hoping django >> > would provide some nice way to do it without me having to explicitly >> > write SQL. The Verb class's __init__ method creates a new Word >> > instance, so that doesn't work, unless there's a way to use it that I >> > don't know about. >> > >> > Any help? >> > >> > Thanks, >> > Matt >> > >> > -- >> > You received this message because you are subscribed to the Google >> > Groups "Django users" group. >> > To post to this group, send email to django-users@googlegroups.com. >> > To unsubscribe from this group, send email to >> > django-users+unsubscr...@googlegroups.com. >> > For more options, visit this group at >> > http://groups.google.com/group/django-users?hl=en. >> > >> > >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Django users" group. >> To post to this group, send email to django-users@googlegroups.com. >> To unsubscribe from this group, send email to >> django-users+unsubscr...@googlegroups.com. >> For more options, visit this group at >> http://groups.google.com/group/django-users?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "Django users" group. > To post to this group, send email to django-users@googlegroups.com. > To unsubscribe from this group, send email to > django-users+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/django-users?hl=en. > -- You received this message because you are subscribed to the Google Groups "Django users" group. 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