I have a model that I would like to use the choices= option for, but three levels deep.
class Doctor(models.Model):
...
zipcode = models.CharField(max_length=10, choices=AREAS, null=True, blank=True)
Within the "zipcode" dropdown in the admin, I would like the hierarchy to be:
Bronx
--Kingsbridge
----10463
----10471
--Fordham
----10458
----10467
----10468
Brooklyn
--Borough Park
----11204
etc.
Then, if I choose zip code 10463, the Doctor object will be associated with the Kingsbridge area in the Bronx. I'm trying this a variety of different ways. The closest I've come is using this:
AREAS = (
('Bronx', (('Kingsbridge', ('10463', '10463'),),)),
...
)
Unfortunately, that gives me this hierarchy:
Bronx
--('10463', '10463')
which is weird and not helpful. Can anybody see where I'm going wrong? Is this hierarchy possible? Would it be smarter to just create another table in the app called Areas and use a manytomany field? The more I think about it, the more I think I have to use a manytomany field. Thanks in advance
As per https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.Field.choices,
it seems to be only 2 level hierarchy is supported. If you need more than 2 levels, you need to use either custom widgets (or) multiple fields with Foreign Key relationships.
Related
I have a product model that has a manytomany relationship to a locations model. I am creating an app for my clients business that has hundreds of products and services, but each product/service have different prices base on the delivery location and can deliver to multiple locations. Right now my client delivers to 4 locations.
Solution #1
Hard code all 4 locations into the product model - this works, but is not preferred since they want to expand and hard coding more locations is just gross..
Solution #2 (current solution - code listed below)
Create a manytomany relationship to locations - this works, but is getting way out of hand having location options of varying charges an rates for - multiplied by every product....
Solution #3 - This is the help I need, if a solution exists.
I would like to build a hybrid of sort of the above two options. Id like to keep the manytomany with the location model so its easy to add locations as they grow, but once added, I would like to have an empty 'price' object that they can fill-in when adding or updating a product, yet remain assigned to that product only.
Not sure if this makes sense, so after my current code below (solution 2 above) I included a sample image to help illustrate my question. Thank you for your help.
Product Model
class Product(models.Model):
...
locations = models.ManyToManyField('Location', related_name='deliver_to')
...
Location Model
LOCATIONS = (
('Los Angeles', 'Los Angeles'),
('Orange County', 'Orange County'),
('Riverside', 'Riverside'),
('San Diego', 'San Diego')
)
class Location(models.Model):
l_title = models.CharField(
max_length=255,
choices=LOCATIONS,
verbose_name='Service Location'
)
...
Using https://docs.djangoproject.com/en/dev/topics/db/models/#intermediary-manytomany will allow for extra fields.
I've got django 1.8.5 and Python 3.4.3, and trying to create a subquery that constrains my main data set - but the subquery itself (I think) needs a join in it. Or maybe there is a better way to do it.
Here's a trimmed down set of models:
class Lot(models.Model):
lot_id = models.CharField(max_length=200, unique=True)
class Lot_Country(models.Model):
lot = models.ForeignKey(Lot)
country = CountryField()
class Discrete(models.Model):
discrete_id = models.CharField(max_length=200, unique=True)
master_id = models.ForeignKey(Inventory_Master)
location = models.ForeignKey(Location)
lot = models.ForeignKey(Lot)
I am filtering on various attributes of Discrete (which is discrete supply) and I want to go "up" through Lot, over the Lot_Country, meaning "I only want to get rows from Discrete if the Lot associated with that row has an entry in Lot_Country for my appropriate country (let's say US.)
I've tried something like this:
oklots=list(Lot_Country.objects.filter(country='US'))
But, first of all that gives me the str back, which I don't really want (and changed it to be lot_id, but that's a hack.)
What's the best way to constrain Discrete through Lot and over to Lot_Country? In SQL I would just join in the subquery (or even in the main query - maybe that's what I need? I guess I don't know how to join up to a parent then down into that parent's other child...)
Thanks in advance for your help.
I'm not sure what you mean by "it gives me the str back"... Lot_Country.objects.filter(country='US') will return a queryset. Of course if you print it in your console, you will see a string.
I also think your models need refactoring. The way you have currently defined it, you can associate multiple Lot_Countrys with one Lot, and a country can only be associated with one lot.
If I understand your general model correctly that isn't what you want - you want to associate multiple Lots with one Lot_Country. To do that you need to reverse your foreign key relationship (i.e., put it inside the Lot).
Then, for fetching all the Discrete lots that are in a given country, you would do:
discretes_in_us = Discrete.objects.filter(lot__lot_country__country='US')
Which will give you a queryset of all Discretes whose Lot is in the US.
Say I have a model that is
class Bottles(models.Model)
BottleCode = models.IntegerField()
class Labels(models.Model)
LabelCode = models.IntegerField()
How do I get a queryset of Bottles where the BottleCode and LabelCode are equal? (i.e. Bottles and Labels with no common Code are excluded)
It can be achieved via extra():
Bottles.objects.extra(where=["Bottles.BottleCode in (select Labels.LabelCode from Labels)"])
You may also need to add an app name prefix to the table names, e.g. app_bottles instead of bottles.
Though #danihp has a point here, if you would often encounter queries like these, when you are trying to relate unrelated models - you should probably think about changing your model design.
So first off, I want to clarify that I am trying to make One-To-Many relationships, not Many-to-One. I already understand how ForeignKeys work.
For the sake of the discussion, I've simplified my models; they're much more field-rich than this in the real implementation.
I have a model, called a ColumnDefinition:
class ColumnDefinition(Model):
column_name = CharField(max_length=32)
column_type = PositiveSmallIntegerField()
column_size = PositiveSmallIntegerField(null=True, blank=True)
I think have a registry. Each registry has a separate set of columns for it's input and output definition. I've put the theoretical "OneToManyField" in there to demonstrate what I'm trying to do.
class Registry(Model):
input_dictionary = OneToManyField(ColumnDefinition)
output_dictionary = OneToManyField(ColumnDefinition)
created_date = DateTimeField(auto_now_add=True, editable=False)
A ColumnDefinition is only ever related to one Registry ever. So it's not a Many to Many relationship. If I put a ForeignKey on the ColumnDefinition instead to create a reverse relationship, it can only create a single reverse, whereas I need both an input and output reverse.
I don't want to have to do anything kludgey like adding a "column_registry_type" field onto ColumnDefinition if I can get around it.
Does anyone have any good ideas on how to solve this problem?
Thanks!
You can add two ForeignKeys on ColumnDefinition, one for input and one for output, and give them separate related_names:
class ColumnDefinition(Model):
...
input_registry = models.ForeignKey(Registry, related_name='input_columns')
output_registry = models.ForeignKey(Registry, related_name='output_columns')
You can then access the set of columns like registry.input_columns.
You can and should define two different ForeignKey fields on ColumnDefinition. Just make sure to specify a related_name value for at least one of them.
https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.ForeignKey.related_name
I have a group of related companies that share items they own with one-another. Each item has a company that owns it and a company that has possession of it. Obviously, the company that owns the item can also have possession of it. Also, companies sometimes permanently transfer ownership of items instead of just lending it, so I have to allow for that as well.
I'm trying to decide how to model ownership and possession of the items. I have a Company table and an Item table.
Here are the options as I see them:
Inventory table with entries for each Item - Company relationship. Has a company field pointing to a Company and has Boolean fields is_owner and has_possession.
Inventory table with entries for each Item. Has an owner_company field and a possessing_company field that each point to a Company.
Two separate tables: ItemOwner and ItemHolder**.
So far I'm leaning towards option three, but the tables are so similar it feels like duplication. Option two would have only one row per item (cleaner than option one in this regard), but having two fields on one table that both reference the Company table doesn't smell right (and it's messy to draw in an ER diagram!).
Database design is not my specialty (I've mostly used non-relational databases), so I don't know what the best practice would be in this situation. Additionally, I'm brand new to Python and Django, so there might be an obvious idiom or pattern I'm missing out on.
What is the best way to model this without Company and Item being polluted by knowledge of ownership and possession? Or am I missing the point by wanting to keep my models so segregated? What is the Pythonic way?
Update
I've realized I'm focusing too much on database design. Would it be wise to just write good OO code and let Django's ORM do it's thing?
Is there a reason why you don't want your item to contain the relationship information? It feels like the owner and possessor are attributes of the item.
class Company(models.Model):
pass
class Item(models.Model):
...
owner = models.ForeignKey(Company, related_name='owned_items')
holder = models.ForeignKey(Company, related_name='held_items')
Some examples:
company_a = Company.objects.get(pk=1)
company_a.owned_items.all()
company_a.held_items.all()
items_owned_and_held_by_a=Items.objects.filter(owner=company_a, holder=company_a)
items_on_loan_by_a=Items.objects.filter(owner=company_a).exclude(holder=company_a)
#or
items_on_loan_by_a=company_a.owned_items.exclude(holder=company_a)
items_a_is_borrowing=Items.objects.exclude(owner=company_a).filter(holder=company_a)
#or
items_a_is_borrowing=company_a.held_items.exclude(owner=company_a)
company_b = Company.objects.get(pk=2)
items_owned_by_a_held_by_b=Items.objects.filter(owner=company_a, holder=company_b)
#or
items_owned_by_a_held_by_b=company_a.owned_items.filter(holder=company_b)
#or
items_owned_by_a_held_by_b=company_b.held_items.filter(owner=company_a)
I think if your items are only owned by a single company and held by a single company, a separate table shouldn't be needed. If the items can have multiple ownership or multiple holders, a m2m table through an inventory table would make more sense.
class Inventory(models.Model):
REL = (('O','Owns'),('P','Possesses'))
item = models.ForeignKey(Item)
company = models.ForeignKey(Company)
relation = models.CharField(max_length=1,choices=REL)
Could be one implementation, instead of using booleans. So I'd go for the first. This could even serve as an intermediate table if you ever decide to use a 'through' to relate items to company like this:
Company:
items = models.ManyToManyField(Item, through=Inventory)
Option #1 is probably the cleanest choice. An Item has only one owner company and is possessed by only one possessing company.
Put two FK to Company in Item, and remember to explicitly define the related_name of the two inverses to be different each other.
As you want to avoid touching the Item model, either add the FKs from outside, like in field.contribute_to_class(), or put a new model with a one-to-one rel to Item, plus the foreign keys.
The second method is easier to implement but the first will be more natural to use once implemented.