Django 根据另一个表中的值过滤表中的数据？

Question

views.py:

def dcuinterval(request):

var7 = dcu.objects.all()
MU_count = Meter_Mapping_Table.objects.filter(DCU_id=dcu.id).count()
d = {
    'MU_count': MU_count, 'var7': var7,
}
return render(request, 'dcu_interval.html', d)

Models.py:

class dcu(models.Model):
id = models.AutoField(unique=True, editable=False, primary_key=True)
Asset = models.CharField(max_length=128)
IMEI_Number = models.CharField(max_length=128)

def __str__(self):
    return self.Asset

class Meter_Mapping_Table(models.Model):

mid = models.AutoField(unique=True, editable=False, primary_key=True)
Meter_id = models.CharField(
    max_length=128, help_text='(ID of the Meter table)')
MU_id = models.CharField(max_length=150)
DCU_id = models.CharField(max_length=150, null=True, blank=False)

def __str__(self):
    return self.Meter_id

how to filter the data based on the another table filed?

i need to filter the DCU_id based on the DCU tables id field DCU_id =1; DCU.id=1; ANSWER: MU_count=1 like this i need to filter and show that count

Answer 1

You can use:

Meter_Mapping_Table.objects.filter(DCU_id='1').count()

Although that is the answer, you need to really consider your database design and make use of ForeignKey relationships. Having a foreign key as a CharField is not recommended.

I would suggest the following:

Change:

DCU_id = models.CharField(max_length=150, null=True, blank=False)

To:

DCU = models.ForeignKey(dcu, null=True, blank=False)

Then you can query like so:

Meter_Mapping_Table.objects.filter(DCU=1).count()

Note: Also consider following Django's Naming Convention for Models . As this will aid readability for other developers.