django unique_together
# Preferred alternative to unique_together, Django 2.2+
# Use the 'constraints' var in class Meta
class Volume(models.Model):
id = models.AutoField(primary_key=True)
journal_id = models.ForeignKey(Journals, db_column='jid', null=True, verbose_name="Journal")
volume_number = models.CharField('Volume Number', max_length=100)
comments = models.TextField('Comments', max_length=4000, blank=True)
class Meta:
constraints = [
models.UniqueConstraint(fields=['journal_id', 'volume_number'], name='name of constraint')
]