python - 尝试通过中间表进行过滤

Question

我正在尝试执行此查询

subsidiaries = self.con.query(Subsidiary)\
                    .options(joinedload(Subsidiary.commerce)\
                             .joinedload(Commerce.commerce_tags))\
                    .filter(CommerceTag.tag_id == id)

但是不行，所以解释一下:

表之间的关系是:

我只想获得所有具有特定标签的商业的所有子公司，我想用 Subsidiary 有基类来做(我知道如果我使用 Commerce 会更容易)，原因是因为我将其转换为具有以下格式的 json 值:

"subsidiaries": [
    {
        "id": 1,
        "name": "some_name",
        "commerce": {
            "id": 1,
            "name": "Commerce Name"
        }
    }
]

好吧，我可以使用 Commerce 的基类进行查询，但我认为可能迭代 commerces 以获取子公司比在查询中这样做更昂贵。

我不想加载 CommerceTag，但我在 joinedload 中加载了它，因为它不适用于 Join 方法。

我需要一些帮助才能做到这一点:(

Answer 1

这样试试:

subsidiaries = session.query(Subsidiary)\
                .join(Subsidiary.commerce)\
                .join(Commerce.commerce_tags)\
                .filter(CommerceTag.id == id)

您的语句生成如下查询:

SELECT subsidiary.id AS subsidiary_id, subsidiary....
FROM tag, subsidiary
LEFT OUTER JOIN commerce AS commerce_1 
    ON subsidiary.id = commerce_1.subsidiary_id
LEFT OUTER JOIN (
    tags_by_commerce AS tags_by_commerce_1
    JOIN tag AS tag_1 ON tag_1.id = tags_by_commerce_1.id_tag
) ON commerce_1.id = tags_by_commerce_1.id_commerce
WHERE tag.id = :id_1

所以标签过滤没有效果。

我提议的声明生成了这个:

SELECT subsidiary.id AS subsidiary_id, subsidiary.name AS subsidiary_name
FROM subsidiary 
JOIN commerce ON subsidiary.id = commerce.subsidiary_id
JOIN tags_by_commerce AS tags_by_commerce_1 ON commerce.id = tags_by_commerce_1.id_commerce
JOIN tag ON tag.id = tags_by_commerce_1.id_tag
WHERE tag.id = :id_1