如何创建两个不同 django 模型的联合？

Question

我有两个 django 模型

class ModelA(models.Model):
    title = models.CharField(..., db_column='title')
    text_a = models.CharField(..., db_column='text_a')
    other_column = models.CharField(/*...*/ db_column='other_column_a')


class ModelB(models.Model):
    title = models.CharField(..., db_column='title')
    text_a = models.CharField(..., db_column='text_b')
    other_column = None 

然后我想使用合并该模型的两个查询集union

ModelA.objects.all().union(ModelB.objects.all())

但在查询中我看到

(SELECT
`model_a`.`title`,
`model_a`.`text_a`,
`model_a`.`other_column`
FROM `model_a`)

UNION
(SELECT
`model_b`.`title`,
`model_b`.`text_b`
FROM `model_b`)

当然我有例外The used SELECT statements have a different number of columns。

如何创建别名和假列以使用联合查询？

Answer 1

您可以对最后一列进行注释，以弥补列号不匹配的情况。

a = ModelA.objects.values_list('text_a', 'title', 'other_column')
b = ModelB.objects.values_list('text_a', 'title')
        .annotate(other_column=Value("Placeholder", CharField()))

# for a list of tuples
a.union(b)

# or if you want list of dict
# (this has to be the values of the base query, in this case a)

a.union(b).values('text_a', 'title', 'other_column')

Answer 2

在SQL查询中，我们可以用来NULL定义剩余的列/别名

(SELECT
`model_a`.`title`,
`model_a`.`text_a`,
`model_a`.`other_column`
 FROM `model_a`)

UNION

(SELECT
`model_b`.`title`,
`model_b`.`text_b`, 
 NULL
 FROM `model_b`)