How to extend an array or append a value to array field on Django ORM's Queryset Update? [Postgresql]

Question

I have an ArrayField to store Colors for a given Dish object in a Schema and the dishes also have a category

class Dish(models.Model):
   colors = ArrayField(models.CharField(max_length=16))
   category = models.CharField(max_length=32) 

Let's say I have 15 Dish objects, out of which 13 belong to the "Cookware" category and the remaining 2 belong to "Modware"

Now I want to append a color to the existing list of colors for a given category in a single update query method (Which has to append my new color to all the array fields of matching Dishes, 13 items in my case)

Following are the ways that I have tried to perform this operation and ended up having errors

• Dish.objects.filter(category="Cookware").update(colors=F("colors")+"red")

• Dish.objects.filter(category="Cookware").update(colors=F("colors")+["red"])

Following is the error message I am facing when I am trying with the above two queries No operator matches the given name and argument types. You might need to add explicit type casts

The following obviously doesn't work as apppend will return None Dish.objects.filter(category="Cookware").update(colors=F("colors").append("red"))

PS: Using Django(3.2), Django ORM, Postgres ArrayField from django.contrib.postgres.fields import ArrayField

Thanks in advance for spending your time to help me solve this.

Answer 1

Using native django field it's impossible as https://code.djangoproject.com/ticket/26355 is open still. To do it you can use django-postgres-extensions lib.

from django_postgres_extensions.models.fields import ArrayField

class Dish(models.Model):
   colors = ArrayField(models.CharField(max_length=16))
   category = models.CharField(max_length=32)

# ...
from django_postgres_extensions.models.functions import ArrayAppend

Dish.objects.filter(category="Cookware").update(colors=ArrayAppend('colors', 'red'))