我需要将原始MySQL查询转换为Django ORM查询

Question

I have models.py that represent below:

from django.db import models
from django.db.models.signals import post_save

# Create your models here.
from django.http import request


class Task(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    description = models.CharField(max_length=512)
    cost = models.DecimalField(decimal_places=2, max_digits=8)

    def __str__(self):
        return self.description + "-" + str(self.cost)


class TaskStatus(models.Model):
    STATUS = (
        (0, 'Created'),
        (1, 'Taken'),
        (2, 'Reissued'),
        (3, 'On approve'),
        (4, 'Done'),
    )
    task_id = models.IntegerField()
    created = models.DateTimeField(auto_now_add=True)
    status = models.PositiveSmallIntegerField(choices=STATUS, default=0)

    def __str__(self):
        return str(self.task_id) + ' ' + str(self.status)

    def create_status(sender, instance, **kwargs):
        if kwargs['created']:
            task_status = TaskStatus.objects.create(task_id=instance.id)

    post_save.connect(create_status, sender=Task)

I have to translate that mysql query to django ORM query. I got stack on this for 2 days. And please suggest me some useful links to understand how to perform.

SELECT t.created,
      t.description,
      (SELECT MAX(s.created)
       FROM task_statuses s
       WHERE s.task_id = t.id AND s.status_type = 3
       GROUP BY s.task_id) as task_on_approve
FROM task t
WHERE t.created BETWEEN '2019-04-01 00:00:00' AND '2019-04-30 23:59:59';

Answer 1

Take a look at the Django docs for Subquery . Link .

In a nutshell, this is what you're looking for:

from django.db import models

Task.objects.filter(created__gte='2019-04-01', created__lt='2019-05-01').annotate(task_on_approve=models.Subquery(TaskStatus.objects.filter(task_id=models.OuterRef('id'), status_type=3).order_by('-created').values('created')[:1], output_field=models.DateTimeField())).values('created', 'description', 'task_on_approve')

Answer 2

Try this. I am tested this code 100% working.

from datetime import datetime
from datetime import timezone

from django.core.management.base import BaseCommand, CommandError
from django.db.models import Avg, Max, Min, Sum, DateTimeField
from django.db.models import OuterRef, Subquery

from app.models import Task, TaskStatus

class Command(BaseCommand):
    def handle(self, *args, **options):

        sub_query = TaskStatus.objects\
            .annotate(max_created_date=Max('created'))\
            .filter(\
                task_id=OuterRef('pk'),
                status=3
            )

        from_datetime = datetime.strptime('2019-04-01 00:00:00', '%Y-%m-%d %H:%M:%S').replace(tzinfo=timezone.utc)
        to_datetime = datetime.strptime('2019-04-30 23:59:59', '%Y-%m-%d %H:%M:%S').replace(tzinfo=timezone.utc)

        query = Task.objects.annotate(
            task_on_approve=Subquery(
                sub_query.values('max_created_date')[:1],
                output_field=DateTimeField()
            )
        ).filter(
            created__range=[
                from_datetime,
                to_datetime
            ]
        )

        print(query.query)

        self.stdout.write('Done.')

Output

SELECT "app_task"."id", "app_task"."created", "app_task"."description", "app_task"."cost", (SELECT MAX(U0."created") AS "max_created_date" FROM "app_taskstatus" U0 WHERE (U0."status" = 3 AND U0."task_id" = ("app_task"."id")) GROUP BY U0."id", U0."task_id", U0."created", U0."status"  LIMIT 1) AS "task_on_approve" FROM "app_task" WHERE "app_task"."created" BETWEEN 2019-04-01 00:00:00 AND 2019-04-30 23:59:59