如何在 Django 中获取 table 内部连接的别名

Question

我正在使用 django 2.1、python 3.6 和 SQL Server 2012 作为后端。我有以下型号：

class ModelA(models.Model):
    name = models.CharField(...)
    value = models.PositiveIntegerField(...)

class ModelB(models.Model):
    name = models.CharField(...)
    values = models.ManyToManyField(ModelA, through='ModelC')

class ModelC(models.Model):
    model_a = models.ForeignKey(ModelA, ...)
    model_b = models.ForeignKey(ModelB, ...)
    info_a = models.CharField(...)
    info_b = models.CharField(...)

如何实现以下 SQL 查询：

SELECT t1.model_a_id AS a_id, t3.value AS a_value
FROM ModelB AS t0
INNER JOIN ModelC t1 ON t1.model_b_id = t0.id
INNER JOIN ModelC t2 ON t2.model_b_id = t0.id
INNER JOIN ModelA t3 ON t3.id = t2.model_a_id
INNER JOIN ModelC t4 ON t4.model_b_id = t0.id
WHERE t1.model_a_id in (1,2) AND t2.model_a_id in (8,9,10,11) AND t4.model_a_id in (21,22)

我目前拥有的：

ModelB.objects.filter(values__in=[1,2]).filter(values__in=[8,9,10,11]).filter(values__in=[21,22])

这会生成正确的过滤查询集。但是我怎样才能得到正确的字段呢？

我尝试使用 annotate 功能，但失败了。如文档中所述使用 django 的 Subquery 会产生数据库错误，因为 SQL 服务器不支持 SELECT 部分中的子查询。

有什么建议吗？谢谢！

Answer 1

您的查询不是最优的，但那是另一个问题。你可以试试raw query

所以你可以运行:

query = """
SELECT t1.model_a_id AS a_id, t3.value AS a_value
FROM ModelB AS t0
INNER JOIN ModelC t1 ON t1.model_b_id = t0.id
INNER JOIN ModelC t2 ON t2.model_b_id = t0.id
INNER JOIN ModelA t3 ON t3.id = t2.model_a_id
INNER JOIN ModelC t4 ON t4.model_b_id = t0.id
WHERE t1.model_a_id in ({0}) AND t2.model_a_id in ({1}) AND t4.model_a_id in 
({2})"""
t1_filters = ','.join(['1','2'])
t2_filters = ','.join(['8', '9', '10', '11'])
t4_filters = ','.join(['21', '22'])

results = ModelA.objects.raw(query.format(t1_filters, t2_filters, t4_filters))
for instance in results.all():
    print(instance)

Answer 2

我解决了它而没有退回到原始 sql。我使用了 django 的 FilteredRealtion 对象结合了额外的 annotate 像这样：

from django.db.models import Q, F, FilteredRelation

qs = ModelB.objects.filter(values__in=[21,22])
qs = qs.filter(values__in=[1,2])
qs = qs.filter(values__in=[8,9,10,11])
qs = qs.annotate(_a_id=FilteredRelation('modelc', condition=Q(values__in=[8,9,10,11])),
                 _a_value=FilteredRelation('modelc', condition=Q(values__in=[1,2])))
qs = qs.annotate(a_id=F('_a_id__model_a'), a_value=F('_a_value__model_a__value'))
qs = qs.values('a_id', 'a_value')

如何在 Django 中获取 table 内部连接的别名

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python

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