Latest objects of every group with Django filter in mysql backend

Question

I have 2 Models:

class WLSDomainName(BaseMixin):
    domain_name = models.CharField('Domain Name',max_length=255, null=False, blank=False)
    site_name = models.CharField('Site Name', max_length=10, choices = SITE_NAME, default='dc',blank=False, null=False)
    delete_status = models.BooleanField(default=False)

class DomainOverallHealthStatus(BaseMixin):
    domain_name = models.ForeignKey(WLSDomainName, on_delete=models.CASCADE, null=True, blank=False, related_name="overall_health_status_domain_name") 
    configuredServerCount = models.IntegerField(blank=True, null=True)
    activeServerCount = models.IntegerField(blank=True, null=True)
    overallServiceHealth = models.CharField(max_length=255, null=True, blank=True)
    activeThreadCount = models.IntegerField(blank=True, null=True)
    activeHttpSessionCount = models.IntegerField(blank=True, null=True)
    classification_time = models.CharField(max_length=20, null=True, blank=True)

I need to find the latest object from DomainOverallHealthStatus model for every object of WLSDomainName.

I have tried:

o_health = DomainOverallHealthStatus.objects.all().values('domain_name').annotate(Max('created')).order_by()

This query returning me only id and created.

<QuerySet [{'domain_name': 1, 'created__max': datetime.datetime(2022, 8, 31, 9, 14, 49, 217073, tzinfo=datetime.timezone.utc)}, {'domain_name': 2, 'created__max': datetime.datetime(2022, 8, 31, 9, 14, 50, 338368, tzinfo=datetime.timezone.utc)}]>

But I need to fetch every column of DomainOverallHealthStatus.

Amrez · Accepted Answer · 2022-08-31 12:28:01Z

1

the query you wanted:

from django.db.models import Max, F

o_health = DomainOverallHealthStatus.objects.alias(
    latest=Max('domain_name__overall_health_status_domain_name__created')
).filter(
    created=F('latest')
)

answered Aug 31, 2022 at 12:28

Amrez

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3 Comments

Samrat Over a year ago

Thanks a lot. My problem is solved. But I am so sorry that I can't understand the query. Can you make me understand?

Amrez Over a year ago

@Samrat for every health status, checks the related domain name and gets highest created field of its health statuses. Then checks created value of health status with the founded created value of previous step, and keeps it if they're equal.

Amrez Over a year ago

if you didn't understand what i said, you can test the query and print its sql query

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