Thanks very much for your help Doug. Do you think there is value in having a generic DAG implementation for Django? Seems to me like it might be a useful addition, but I'm curious as to how useful it would be given that most non-Django implementations I have come across are as you describe 'very domain specific'.
I also wonder how much a DAG implementation should rely on RDMS functions to minimize the chatter between the application and database. For instance, it would be terrible to get a node from the DB, determine it's parent(s), fetch each parent from the DB, determine *its* parents, etc. etc. Now I could serialize the parents into the node data, but don't know if that is going to be effective because if the parent relationships change you're going to have a lot of processing to update all your nodes. I know that a DAG is a subset of a digraph, which is what an RDBMS is, so I'm sure that there's a very elegant way of doing it. But the problem for me is (a)determining how to do it from the database perspective, and (b)how to do it in Django. Cheers, Paul On Sep 18, 8:34 am, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > We use a Tree for the navigation bar (not a true DAG, but there are > circular > checks):https://pycon.coderanger.net/browser/django/trunk/pycon/navbar/models.py > > There is a validator IsNotCircular, which does the obvious. > > There is code to do serialization (currently just a pickle), but there > are plans to add json to communicate to the client. > The (poor) documentation on using the navbar is > here:https://pycon.coderanger.net/wiki/PyCon08/NavBar > > I have other examples of true DAG's in DB form, but they are very > domain specific and take advantage of the > limitations in the data. (like the divided room problem where a > conference room might have 3 parts which can > make a total of 6 'rooms', but have special meaning for room > scheduling). But the NavBar is closest to what > you are trying to do. > > On Sep 17, 4:08 pm, "paul.dorman" <[EMAIL PROTECTED]> wrote: > > > Thanks for your response Julio, > > > something similar yes. What I'm after is an Django implementation of > > andirectedacyclic graph. I understand there's some complexity > > involved to ensure no cycles can be created (which I understand is the > > graph equivalent of an endless loop). There's plenty of good examples > > of DAG out there, but I'm not sure how to implement one that works > > with RDMS (or Django for that matter!) > > > Paul > > > On Sep 17, 4:56 pm, Julio César Carrascal Urquijo > > > <[EMAIL PROTECTED]> wrote: > > > I'm a newbie on Django my self but maybe this is what you are looking > > > for: > > > > class Category(models.Model): > > > code = models.CharField(maxlength=200, unique=True) > > > products = models.ManyToManyField('Product') > > > > class Product(models.Model): > > > parent = models.ForeignKey('Post') > > > code = models.CharField(maxlength=200, unique=True) > > > > I've also read that you can specify signals for most operations on a > > > model (Like when a model is inserted, updated or deleted from the > > > database) though I can't find the URL right now. There's some mention > > > of it here: > > > >http://www.djangoproject.com/documentation/db-api/ > > > > On Sep 16, 9:54 pm, "Paul Dorman" <[EMAIL PROTECTED]> wrote: > > > > > Hi all, > > > > > definite newbie here. I'd like to implement a category type system in > > > > Django. I've looked in the cookbook and Googled a bit, but to no avail. > > > > What > > > > I'm after should be pretty simple: adirectedgraph for categories, where > > > > objects and perhaps categories can be a member of one or more > > > > categories. > > > > For example, a 'server' is an 'infrastructure component' (for the > > > > techies), > > > > as well as an 'asset' (for the financial types). In my grand scheme > > > > when an > > > > object is associated with one or more categories (one is the minimum), > > > > the > > > > application will execute method calls stored (with optional > > > > parameters) in > > > > the database (serialized as JSON or XML). With the 'server' example, it > > > > might be that being in the 'infrastructure component' category triggers > > > > an > > > > email to be sent to the system administrator, and the existence in the > > > > 'asset' category would trigger an automated update to the asset > > > > register. > > > > The methods are stored according to the standard CRUD set of > > > > operations, so > > > > that a user can create a new category in the view, and then specify > > > > actions > > > > which occur when an object is created, read, updated, or deleted > > > > (provided > > > > by the application itself). Actions are triggered for both objects (the > > > > things that are categorized) and for child categories (so for example > > > > it may > > > > be that a parent category can be locked in such a way as to prevent any > > > > more > > > > child categories from being added). > > > > > Note that categories are purely containers with generic actions (for > > > > crud > > > > operations on objects in the category) and distinct from objects, which > > > > I > > > > imagine would have a category_id FK. And note also that my objects are > > > > all > > > > using the same model, with the bulk of data serialized as XML. > > > > > Has anyone out there in Djangoland done something like this? The > > > > graph's the > > > > thing - I'm happy to deal with the CRUD triggers myself. If there's a > > > > model > > > > out there that would be a good starting point that would be great. > > > > > One additional thing I'm wondering about is how Django can work with > > > > stored > > > > procedures. For example, it might be more efficient if the application > > > > can > > > > ask the database for the methods to run when an object is created, and > > > > have the database return the methods for not only the object's > > > > bottom-level > > > > category, but for all parent categories as well. > > > > > P.S. > > > > > Congratulations on the great sprint! > > > > > P.P.S. I hope I haven't just embarrassed myself with my naïveté. > > > > > -- > > > > "Science fiction writers are the only ones who care about the future" > > > > -- Kurt Vonnegut --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
