Django model with a list

Question

How to implement a list in a Django model?

Lets say I have a UserProfile model, and each user can have a list of mortgages (undefined quantity) defined by MortgageModel.

class MortgageModel(models.Model):
   bank_name = models.CharField(max_length=128)
   sum = models.BigIntegerField()

class UserProfile(models.Model):
   user = models.OneToOneField(User, on_delete=models.CASCADE)
   # list of morgtages?

my only idea is to make a old school list, where every mortgage can point to another one or null, like this:

class MortgageModel(models.Model):
   bank_name = models.CharField(max_length=128)
   sum = models.BigIntegerField()
   next_mortgage = MortgageModel(null=True, default=null)

class UserProfile(models.Model):
   user = models.OneToOneField(User, on_delete=models.CASCADE)
   mortgages = MortgageModel(null=True, default=null)

is there any other possibility?

Why not just use a ForeignKey relationship between UserProfile and MortgageModel? — perfect5th
– perfect5th, Commented Aug 31, 2016 at 21:16
In order to make a ForeignKey relation I would have to use filters to iterate over mortgages. Wouldn't it be faster to use a list? — user2449761
– user2449761, Commented Aug 31, 2016 at 22:14
A Django model is a Python representation of a database record. A model's fields (e.g. CharField) can only include data types that can be saved in database columns (e.g. character, integer, etc.) A Python list is not a data type that is represented in most common databases (ignoring the idea of a list serialised to XML/JSON/etc.) — ropable
– ropable, Commented Sep 1, 2016 at 2:00

rafaelc · Accepted Answer · 2016-08-31 21:17:02Z

3

You'll have to assign a ForeignKey to User , so that each Mortgate 'belongs' to a user. That is how a One-To-Many relationship is done. Then, if you want to get the list of Mortgages a user have, you'd filter them out like MortgageModel.objects.filter(related_user=user)

So, you'd have something like

Model

   class MortgageModel(models.Model):
       bank_name = models.CharField(max_length=128)
       sum = models.BigIntegerField()
       related_user = models.ForeignKey(UserProfile)

    class UserProfile(models.Model):
       user = models.OneToOneField(User, on_delete=models.CASCADE)

View

list_of_mortages = MortgageModel.objects.filter(related_user=user)

edited Aug 31, 2016 at 21:17

answered Aug 31, 2016 at 21:14

rafaelc

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5 Comments

user2449761 Over a year ago

how to iterate mortgages?

rafaelc Over a year ago

@user2449761 You can query them out using filters.

user2449761 Over a year ago

Thank you for comprehensive answer!

user2449761 Over a year ago

Wouldn't "oldschool" list be faster than filters?

rafaelc Over a year ago

@user2449761 oldschool list means wrong database modeling ;) Take a look at database normalization (good place to start en.wikipedia.org/wiki/Database_normalization)

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