Django Model Relation entries - django

Question

I have data and I want to organize it as:
I create three tables, on for MonthsM, Wellinfo and TestPRODM:
class MonthsM(models.Model):
MonthsM = models.DateTimeField(unique=True)
class Wellinfo (models.Model):
WellID = models.CharField(max_length=15,unique=True)
class TestPRODM(models.Model):
WellID = models.ForeignKey(Wellinfo ,to_field='WellID', on_delete=models.CASCADE)
TestMonth = models.ForeignKey(TestMonthM, on_delete=models.CASCADE)
TestOIL = models.DecimalField(max_digits=10, decimal_places=3,null=True, blank=True)
#conditions
In my real data I have one WellID that can be tested only once in month.
so how to set a condition that do that?
so in the table (TestPRODM) it can have many entry with same WellID but with different months
and so it can have many entry with same TestMonth but with different WellID.
NB. NO entry in (TestPRODM) table that have the same WellID and TestMonth in the same time.
Updated POST
for i ,value in enumerate(PUITS):
try:
_, create = TestPRODM.objects.update_or_create(
WellID= PUITS[i],
TestMonth_id =obj.id,
TestOIL =float(QHUILE[i]),
)
print('Saving', PUITS[i])
AddedList +=[value]
except:
print('Passed', PUITS[i])
pass
and this function pass all restrictions in model and save all data in database!

Answer 1

You make the combination of WellID and TestMonth unique, with a UniqueConstraint [wiki]:
class TestPRODM(models.Model):
WellID = models.ForeignKey(
Wellinfo,
to_field='WellID',
on_delete=models.CASCADE
)
TestMonth = models.ForeignKey(
TestMonthM,
on_delete=models.CASCADE
)
TestOIL = models.DecimalField(
max_digits=10,
decimal_places=3,
null=True,
blank=True
)
class Meta:
constraints = [
models.UniqueConstraint(
fields=['WellID', 'TestMonth'],
name='once_per_month'
)
]
prior to django-2.2, you can make use of unique_together [Django-doc]:
class TestPRODM(models.Model):
WellID = models.ForeignKey(
Wellinfo,
to_field='WellID',
on_delete=models.CASCADE
)
TestMonth = models.ForeignKey(
TestMonthM,
on_delete=models.CASCADE
)
TestOIL = models.DecimalField(
max_digits=10,
decimal_places=3,
null=True,
blank=True
)
class Meta:
unique_together=[['WellID', 'TestMonth']]
Note: normally the name of the fields in a Django model are written in snake_case, not PerlCase, so it should be: test_month instead of TestMonth.