django - 用 Django 中的 jsonb 字段过滤子查询的计数进行注释

Question

我有一个带有 jsonb 字段的模型。此 jsonb 字段中有一个值可以在其他行之间共享。我试图在按此 jsonb 字段过滤时获取子查询的计数。

我一直在尝试从这篇文章中借用示例的一些伪代码。

alpha_qs = MyModel.objects.filter(class_id="ALPHA")
# unnest jsonb field so I can leverage it via OuterRef
alpha_qs = alpha_qs.annotate(nested_value_id=KeyTextTransform("nested_value_id", "a_jsonb_field"))
related_beta_subquery = MyModel.objects.filter(class_id="BETA", a_jsonb_field__nested_value_id=OuterRef("nested_value_id"))
related_beta_subquery_count = related_beta_subquery.annotate(count=Count("*")).values("count")
alpha_qs = alpha_qs.annotate(related_beta_count=Subquery(related_beta_subquery))

使用此示例数据，我希望顶部实例具有related_beta_countof，2因为有两个关联的 beta 具有相同的nested_value_id.

{
  "class_id": "ALPHA",
  "a_jsonb_field": {
    "nested_value_id": 'abc'
  }
}

{
  "class_id": "BETA",
  "a_jsonb_field": {
    "nested_value_id": 'abc'
  }
}
{
  "class_id": "BETA",
  "a_jsonb_field": {
    "nested_value_id": 'abc'
  }
}
{
  "class_id": "BETA",
  "a_jsonb_field": {
    "nested_value_id": 'zyz'
  }
}

我在下面遇到错误，但无法解决。

ProgrammingError: operator does not exist: jsonb = text
LINE 1: ...d AND (U0."a_jsonb_field" -> 'nested_value_id') = ("my_model...
                                                             ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.

Answer 1

我让它在我的用例中工作。我不认为自己精通 Django，所以可能有一种更简洁的方法来实现这一点。

# Get initial queryset
alpha_qs = MyModel.objects.filter(class_id="ALPHA")
# Pull nested jsonb value out via annotation/KeyTextTransform
alpha_qs = alpha_qs.annotate(nested_value_id=KeyTextTransform("nested_value_id", "a_jsonb_field"))
related_beta_subquery = (
    MyModel.objects.filter(
        class_id="BETA"
    )
    # Pull out nested jsonb for subquery as well
    .annotate(
        nested_value_id=KeyTextTransform("nested_value_id", "a_jsonb_field")
    )
    # Filter to ensure these BETA models have a matched nested_value_id to my ALPHA models
    .filter(
        nested_value_id=OuterRef("nested_value_id")
    )
    # This was honestly the harder part that took a lot of trial and error
    .order_by()
    .values("nested_value_id")
    .annotate(count=Count("*"))
    .values("count")
)
alpha_qs = alpha_qs.annotate(
    count=Case(
        # This Case statement is mostly just bulletproofing. May be unnecessary for your use case
        When(a_jsonb_field__has_key="nested_value_id", then=Subquery(related_beta_subquery)),
        default=Value(0),
        output_field=IntegerField(),
    )
)