Django and PostgreSQL composite types

PostgreSQL has this nifty feature called composite types that you can use to create your own types from the built-in PostgreSQL types. It’s a bit like hstore, only structured, which makes it great for structured data that you might reuse multiple times in a model, like addresses.

Unfortunately to date, they were pretty much a pain to use in Django. There were some older implementations for versions of Django before 1.7, but they tended to do things like create surprise new objects in the namespace, not be migrateable, and require connection to the DB at any time (i.e. during your build).

Anyway, after reading a bunch of their implementations and then the Django source code I wrote django-postgres-composite-types.

Install with:

pip install django-postgres-composite-types

Then you can define a composite type declaratively:

from django.db import models
from postgres_composite_type import CompositeType


class Address(CompositeType):
    """An address."""

    address_1 = models.CharField(max_length=255)
    address_2 = models.CharField(max_length=255)

    suburb = models.CharField(max_length=50)
    state = models.CharField(max_length=50)

    postcode = models.CharField(max_length=10)
    country = models.CharField(max_length=50)

    class Meta:
        db_type = 'x_address'  # Required

And use it in a model:

class Person(models.Model):
    """A person."""

    address = Address.Field()

The field should provide all of the things you need, including formfield etc and you can even inherit this field to extend it in your own way:

class AddressField(Address.Field):
    def __init__(self, in_australia=True, **kwargs):
        self.in_australia = in_australia

        super().__init__(**kwargs)

Finally to set up the DB there is a migration operation that will create the type that you can add:

import address
from django.db import migrations


class Migration(migrations.Migration):

    operations = [
        # Registers the type
        address.Address.Operation(),
        migrations.AddField(
            model_name='person',
            name='address',
            field=address.Address.Field(blank=True, null=True),
        ),
    ]

It’s not smart enough to add it itself (can you do that?). Nor would it be smart enough to write the operations to alter a type. That would be a pretty cool trick. But it’s useful functionality all the same, especially when the alternative is creating lots of 1:1 models that are hard to work with and hard to garbage collect.

It’s still pretty early days, so the APIs are subject to change. PRs accepted of course.

Author: Danielle

Danielle is an Australian software engineer, computer scientist and feminist. She doesn't really work on GNOME any more (sadly). Opinions and writing are solely her own and so not represent her employer, the GNOME Foundation, or anyone else but herself. View all posts by Danielle