django orm 如何确保 postgres 数组字段不是空列表？

Question

I have the following model for django . This model creates an array field called metric_vals but it is allowing the array to be an empty array. Is there a way of making sure the array is always a non empty array?

from django.db import models
import uuid
from django.contrib.postgres.fields import ArrayField

class SampleModel(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    metric_vals = ArrayField(models.FloatField(null=False), null=False, default=list)

Answer 1

You can use the validators kwarg:

from django.contrib.postgres.validators import ArrayMaxLengthValidator, ArrayMinLengthValidator


def get_default_list():
    return [float(1), float(2)]

class SampleModel(models.Model):
    metric_vals = ArrayField(
        models.FloatField(null=False), 
        null=False, 
        # ensure the default passes the validation
        default=get_default_list,
        # like this
        validators=[
           ArrayMinLengthValidator(2),
           ArrayMaxLengthValidator(10),
        ]
    )

Related:

• https://docs.djangoproject.com/en/4.1/ref/validators/

Answer 2

Something like this:

from django.core.exceptions import ValidationError

class SampleModel(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    metric_vals = ArrayField(models.FloatField(null=False), null=False, default=list)

    def save(self, *args, **kwargs):
        if self.metric_vals == []:
            raise ValidationError('Empty list not allowed')

        super().save(*args, **kwargs)