单个查询中的两个注释 [英] Two annotations in a single query

问题描述

我正在尝试构建一个查询集来进行计数，该查询集涉及三个模型.

class Owner(models.Model):name = models.CharField(max_length=10, null=False)

class Location(models.Model):name = models.CharField(max_length=10, null=False)owner = models.ForeignKey(Owner, on_delete=models.SET_NULL, null=True, blank=True)

类资产(models.Model):name = models.CharField(max_length=10, null=false)owner = models.ForeignKey(Owner, on_delete=models.SET_NULL, null=True, blank=True)location = models.ForeignKey(Location, on_delete=models.SET_NULL, null=True, blank=True)

我正在尝试对所有者的位置和所有者的资产进行计数，我可以将其作为两个单独的查询集实现，如下所示:

locations = Owner.objects.all().annotate(locations=Count('location'))

assets = Owner.objects.all().annotate(assets=Count('asset'))

这很好用，但我想要做的是为两个值获取一行并构建一个类似于下面的表.

<代码>|业主 |资产 |地点 ||--------+--------+-----------||所有者1 |10 |3 ||业主2 |100 |20 ||业主3 |70 |50 |

我试图将两个注释放在一个查询中，但我似乎没有得到正确的结果，资产和位置的计数要么相同，要么我得到非常大的数字，我认为这是因为两者都计数操作相互影响.

下面的查询为我提供了相同的资产和位置数字

queryset = Owner.objects.all().annotate(assets=Count('asset'),locations=Count('location'))

或

下面的查询为我提供了大量的资产和位置数据

queryset = Owner.objects.all().annotate(assets=Count('asset')).annotate(locations=Count('location'))

我可以直接用 SQL 做到这一点，但我希望不要走这条路.

解决方案

谢谢 Nara，我尝试了你建议的不同排列，最终奏效.

queryset = Owner.objects.all().annotate(assets=Count('asset', distinct=True), location=Count('location', distinct=True))

这是 Django shell 中的样子.

<预><代码>>>>从库存.模型导入 *>>>从 django.db.models 导入计数>>>queryset = Owner.objects.all().annotate(assets=Count('asset', distinct=True), location=Count('location', distinct=True))>>>变量(查询集 [0]){'_state': <django.db.models.base.ModelState object at 0x0427B230>, 'id': 1, 'name': 'Owner 1', 'assets': 5, 'locations': 4}>>>变量(查询集 [1]){'_state': <django.db.models.base.ModelState object at 0x0427B2D0>, 'id': 2, 'name': 'Owner 2', 'assets': 3, 'locations': 4}>>>变量(查询集 [2]){'_state': <django.db.models.base.ModelState object at 0x0427B4D0>, 'id': 3, 'name': 'Owner 3', 'assets': 2, 'locations': 6}

如您所见，这同时为我提供了资产和位置计数.

I am trying to build a query set to do a count, the query set involves three models.

class Owner(models.Model): name = models.CharField(max_length=10, null=False)

class Location(models.Model): name = models.CharField(max_length=10, null=False) owner = models.ForeignKey(Owner, on_delete=models.SET_NULL, null=True, blank=True)

class Asset(models.Model): name = models.CharField(max_length=10, null=false) owner = models.ForeignKey(Owner, on_delete=models.SET_NULL, null=True, blank=True) location = models.ForeignKey(Location, on_delete=models.SET_NULL, null=True, blank=True)

I am trying to do a count for Locations for the owner and Assets for the owner, I can achieve this as two separate Querysets as follows:

locations = Owner.objects.all().annotate(locations=Count('location'))

assets = Owner.objects.all().annotate(assets=Count('asset'))

This works fine, but what I'm trying to do is get a single row for both values and build a table similar to the one below.

| Owner | Assets | Locations | |--------+--------+-----------| | owner1 | 10 | 3 | | owner2 | 100 | 20 | | owner3 | 70 | 50 |

I've tried to put both annotations in a single query but I don't appear to get the right results, the count is either the same for both assets and location or I get very large numbers which I assume because both count operations are impacting each other.

Query below gives me the same numbers for both asset and location

queryset = Owner.objects.all().annotate(assets=Count('asset'), locations=Count('location'))

or

Query below gives me large numbers for both asset and location

queryset = Owner.objects.all().annotate(assets=Count('asset')).annotate(locations=Count('location'))

I can do this directly with SQL but I'm hoping not do go down that path.

解决方案

Thanks Nara, I tried a different permutation of what you suggested which ended up working.

queryset = Owner.objects.all().annotate(assets=Count('asset', distinct=True), locations=Count('location', distinct=True))

Here is what it looks like from a Django shell.

>>> from inventory.models import *
>>> from django.db.models import Count
>>> queryset = Owner.objects.all().annotate(assets=Count('asset', distinct=True), locations=Count('location', distinct=True))
>>> vars(queryset[0])
{'_state': <django.db.models.base.ModelState object at 0x0427B230>, 'id': 1, 'name': 'Owner 1', 'assets': 5, 'locations': 4}
>>> vars(queryset[1])
{'_state': <django.db.models.base.ModelState object at 0x0427B2D0>, 'id': 2, 'name': 'Owner 2', 'assets': 3, 'locations': 4}
>>> vars(queryset[2])
{'_state': <django.db.models.base.ModelState object at 0x0427B4D0>, 'id': 3, 'name': 'Owner 3', 'assets': 2, 'locations': 6}

As you can see that gives me both the asset and the location counts.

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