Flexible database models for users to define extra columns to database tables in Django

Question

I am trying to build a tool that, at a simple level, tries to analyse how to buy a flat. DB = POSTGRES

So the model basically is:

class Property(models.Model):
    address = CharField(max_length = 200)   
    price = IntegerField()
    user = ForeignKey(User)     # user who entered the property in the database
    #..
    #..
    # some more fields that are common across all flats



    #However, users might have their own way of analysing 

    # one user might want to put

    estimated_price = IntegerField() # his own estimate of the price, different from the zoopla or rightmove listing price
    time_to_purchase = IntegerField()  # his own estimate on how long it will take to purchase


    # another user might want to put other fields
    # might be his purchase process requires sorting or filtering based on these two fields

    number_of_bedrooms = IntegerField()
    previous_owner_name = CharField()

How do I give such flexiblity to users? They should be able to sort , filter and query their own rows (in the Property table) by these custom fields. The only option I can think of now is the JSONField Postgres field

Any advice? I am surprised this is not solved readily in Django - I am sure lots of other people would have come across this problem already

Thanks

Sidhin S Thomas · Accepted Answer · 2017-10-28 12:56:45Z

1

Edit: As the comments point out. JSON field is a better idea in this case.

Simple. Use Relations.

Create a model called attributes.

It will have a foreign key to a Property, a name field and a value field.

Something like,

class Attribute(models.Model):
    property = models.ForiegnKey(Property)
    name = models.CharField(max_length=50)
    value = models.CharField(max_length=150)

Create an object each for all custom attributes of a property.

When using database queries use select_related of prefetch_related for faster response, less db operations.

edited Oct 28, 2017 at 12:56

answered Jul 29, 2017 at 15:52

Sidhin S Thomas

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2 Comments

Adam Johnson Over a year ago

This is known as Entity Attribute Value, or EAV modelling. Using a JSONField is a better option than this, you can index columns of a JSONField if they become popular.

dyve Over a year ago

We've done a few EAV implementations with relations. It works, it scales, but when it gets really big it tends to get overwhelming. We've started working on a JSON solution: github.com/zostera/django-jeaves

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