Hi Tim,
Thanks for the concrete examples. I actually had exactly what you had coded
last night, but I got rid of it because having multiple inventories for a
single samurai seemed counter-intuitive to me. But it sounds like it's the
best way to get the granularity I want.
Going back to that system I have a different problem then. If I want to list
all of the items that a samurai has in his inventory I would like to use a
samurai.item_set method, but this method fails with multiple inventories. It
also didn't seem to work with a samurai.inventory_set method.
I'm okay with having multiple inventories for one samurai, but what is the
best practice for accessing them all as one inventory?
I apologize for the intensive questioning. I hope this discussion is helping
other users who are new to django. I had searched extensively for django
implementations of RPG-like inventories and characters and didn't find any.
I'm sure there are other people in the same boat.
Cheers.
-Tim
On Fri, Feb 19, 2010 at 7:49 AM, Tim Shaffer <timster...@gmail.com> wrote:
> Basically what you are trying to do is called a many-to-many
> relationship with an intermediary table.
>
> If it was a regular many-to-many relationship, you could just do
> ManyToManyField(Item) on the samurai model, and there would be a table
> with a foreign key to item, and a foreign key to samurai, and nothing
> else. But since you need to specify attributes about each of those
> relationships (in this case, condition), you have to use an
> intermediary table (Inventory) with those foreign keys, plus your
> additional attributes. It's not uncommon thing to do at all.
>
> So if you are using an Inventory class like that, you would want to
> have this:
>
> item = models.ForeignKey(Item)
>
> instead of this:
>
> item_id = models.ManyToManyField(Item)
>
> Think of one inventory record as one item belonging to one samurai,
> with a condition. So if a samurai has more than one of the same same
> item, he would have more than one inventory record.
>
> If you were creating your models starting from scratch, you might come
> up with Inventory usage that looks something like this (pseudo code):
>
> Inventory.create(samurai='Tim', item='Item 1', condition='100%')
> Inventory.create(samurai='Tim', item='Item 1', condition='75%')
> Inventory.create(samurai='Tim', item='Item 2', condition='100%')
>
> Looking at this, you can determine that each inventory has only one
> item (foreign key to item), one samurai (foreign key to samurai), and
> one condition (just an integer). So then you can take that and
> translate it to a Django model:
>
> class Inventory(models.Model):
> samurai = models.ForeignKey('Samurai')
> item = models.ForeignKey(Item)
> condition = models.IntegerField(default=100, blank=True,
> verbose_name='condition')
>
> Hope this helps.
>
> On Feb 19, 3:53 am, Timothy Kinney <timothyjkin...@gmail.com> wrote:
> > Okay, I'm still lacking understanding on the inventory part. Here's what
> I
> > have so far:
> >
> > class Inventory(models.Model):
> > id = models.AutoField(primary_key=True, verbose_name="inventory")
> > samurai_id = models.ForeignKey('Samurai')
> > item_id = models.ManyToManyField(Item)
> > condition = models.IntegerField(default=100, blank=True,
> > verbose_name='condition')
> >
> > This has almost all the functionality I want. I can assign a single
> > inventory to a single samurai, and I can add multiple items to the
> > inventory. The problem is that I can't associate a unique condition (100%
> or
> > less) with each item. And I can't seem to add the same item twice.
> >
> > I would like to have an inventory that looked like this:
> >
> > Inventory for Samurai Sam:
> > (item - condition)
> > Item1 - 100%
> > Item1 - 75%
> > Item2 - 100%
> >
> > -Tim
> >
> > On Thu, Feb 18, 2010 at 7:27 PM, Tim Shaffer <timster...@gmail.com>
> wrote:
> > > 1) You can change this in your model. Check out "verbose_name" and
> > > "verbose_name_plural" for the model's Meta class.
> >
> > >http://docs.djangoproject.com/en/dev/ref/models/options/
> >
> > > 2) If you have a ManyToMany field to samurai on the item, you don't
> > > need the inventory model at all. A samurai's inventory could be
> > > obtained by doing "samurai.item_set" and it would return all their
> > > items. There are different reasons to do each one. However.....
> >
> > > 3) Duplicates can be done by using the Inventory model. You could
> > > either add a new field called quantity, or simply have multiple
> > > Inventory records per item and samurai. If each item can have specific
> > > attributes (for example, I can have 2 of the same item, one of which
> > > has 55% durability, and the other has 70% durability) you would want
> > > to have separate records, and could put these attributes on the
> > > inventory model or item model. But if each item is the same, it's
> > > easier to just use a quantity field.
> >
> > > 4) If status is a field that could have changing options, create a
> > > Status model and do a ForiegnKey(Status) on the item. If the choices
> > > aren't going to change frequently, the choices field could be an
> > > Integer or String field and use the Django choices functionality.
> >
> > >http://www.djangoproject.com/documentation/models/choices/
> >
> > > I gather that you may not have a ton of experience working with
> > > relational databases. Perhaps an article on basic database design
> > > might help. It's best to really understand how a relational database
> > > works and should be designed before trying to work with Django's ORM.
> >
> > >http://www.deeptraining.com/litwin/dbdesign/FundamentalsOfRelationalD.
> ..
> >
> > > On Feb 18, 3:17 pm, Timothy Kinney <timothyjkin...@gmail.com> wrote:
> > > > Hello, I'm new to Django, but learning as fast as I can. I would
> > > > appreciate some technical help and some database design advice...
> >
> > > > **
> > > > 1) Admin pluralizing question
> >
> > > > So I have three models: samurai, item, inventory
> >
> > > > When I login to the admin screen it has chosen to pluralize them as:
> > > > samurais, items, inventorys
> >
> > > > I'm a little bit anal, so this bothers me. Where can I change it to:
> > > > samurai, items, inventories ?
> >
> > > > **
> > > > 2) Model relationships question
> >
> > > > Can someone validate that I am using the right relations for these?
> > > > Users will login with a unique id and instantiate a samurai, each
> > > > possessing various attributes (not shown below). Items have unique
> IDs
> > > > but many samurai can have many of the same items (including
> > > > duplicates)- also the items have a status as to the condition of the
> > > > item. There is one inventory for each samurai which links his items
> to
> > > > him. Based on this system, I believe I should do the following...
> >
> > > > Samurai model: AutoField ID (primary key, unique)
> > > > Item model: AutoField ID (primary key, unique), ManyToMany(Samurai)
> > > > Inventory: Foreignkey(Samurai), ManyToMany(Item)
> >
> > > > Did I do this right?
> >
> > > > **
> >
> > > > And two design questions:
> >
> > > > 3) How should I implement duplicates of items for a single inventory?
> > > > For example, one samurai may have two identical fish. Should I store
> > > > this as an additional field in the inventory? If so, how do I link it
> > > > to the item id? Is it cleaner/faster/better to use a dictionary?
> > > > Actually, I've never heard of a dict in SQL.
> >
> > > > 4) How should I implement the status/condition of the items? For
> > > > example, I want them to be "New", "Used", or "Broken/Unusable".
> Should
> > > > I store this in the inventory or in a separate model called Status?
> If
> > > > the latter, should I use a foreignkey(item) and OneToOne(Inventory)
> or
> > > > something else?
> >
> > > > Thank you very much for your help. If you are aware of any tutorials
> > > > or available source code for coding RPGs, browser games, or
> > > > inventories, I will be happy to follow links and try to learn on my
> > > > own.
> >
> > > > -Tim
> >
> > > --
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