Maybe I misunderstand the purpose of Django's update_or_create Model method.
Here is my Model:
from django.db import models
import datetime
from vc.models import Cluster
class Vmt(models.Model):
added = models.DateField(default=datetime.date.today, blank=True, null=True)
creation_time = models.TextField(blank=True, null=True)
current_pm_active = models.TextField(blank=True, null=True)
current_pm_total = models.TextField(blank=True, null=True)
... more simple fields ...
cluster = models.ForeignKey(Cluster, null=True)
class Meta:
unique_together = (("cluster", "added"),)
Here is my test:
from django.test import TestCase
from .models import *
from vc.models import Cluster
from django.db import transaction
# Create your tests here.
class VmtModelTests(TestCase):
def test_insert_into_VmtModel(self):
count = Vmt.objects.count()
self.assertEqual(count, 0)
# create a Cluster
c = Cluster.objects.create(name='test-cluster')
Vmt.objects.create(
cluster=c,
creation_time='test creaetion time',
current_pm_active=5,
current_pm_total=5,
... more simple fields ...
)
count = Vmt.objects.count()
self.assertEqual(count, 1)
self.assertEqual('5', c.vmt_set.all()[0].current_pm_active)
# let's test that we cannot add that same record again
try:
with transaction.atomic():
Vmt.objects.create(
cluster=c,
creation_time='test creaetion time',
current_pm_active=5,
current_pm_total=5,
... more simple fields ...
)
self.fail(msg="Should violated integrity constraint!")
except Exception as ex:
template = "An exception of type {0} occurred. Arguments:\n{1!r}"
message = template.format(type(ex).__name__, ex.args)
self.assertEqual("An exception of type IntegrityError occurred.", message[:45])
Vmt.objects.update_or_create(
cluster=c,
creation_time='test creaetion time',
# notice we are updating current_pm_active to 6
current_pm_active=6,
current_pm_total=5,
... more simple fields ...
)
count = Vmt.objects.count()
self.assertEqual(count, 1)
On the last update_or_create call I get this error:
IntegrityError: duplicate key value violates unique constraint "vmt_vmt_cluster_id_added_c2052322_uniq"
DETAIL: Key (cluster_id, added)=(1, 2018-06-18) already exists.
Why didn't wasn't the model updated? Why did Django try to create a new record that violated the unique constraint?
You should separete your field:
for example: If I have the model:
And I want to search for username = 'Nikolas' and update this instance nickname to 'Nik'(if no User with username 'Nikolas' I need to create it) I should write this code:
see in https://docs.djangoproject.com/en/2.0/ref/models/querysets/
The
update_or_create(defaults=None, **kwargs
) has basically two parts:**kwargs
which specify the "filter" criteria to determine if such object is already present; anddefaults
which is a dictionary that contains the fields mapped to values that should be used when we create a new row (in case the filtering fails to find a row), or which values should be updated (in case we find such row).The problem here is that you make your filters too restrictive: you add several filters, and as a result the database does not find such row. So what happens? The database then aims to create the row with these filter values (and since
defaults
is missing, no extra values are added). But then it turns out that we create a row, and that the combination of thecluster
andadded
already exists. Hence the database refuses to add this row.So this line:
Is to semantically approximately equal to:
(but the original call is typically done in a single query).
You probably thus should write:
(or something similar)