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 > an directed acyclic 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: a directed graph 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 -~----------~----~----~----~------~----~------~--~---
