如何使用 SQLAlchemy 进行批量“SELECT”查询？答案

【问题标题】：How to make bulk `SELECT` queries with SQLAlchemy?如何使用 SQLAlchemy 进行批量“SELECT”查询？
【发布时间】：2022-01-31 16:19:46
【问题描述】：

我有一个简单的查询，例如：

query = """SELECT (A.name, A.food) FROM animals AS A
    WHERE
        A.type = :animal_type AND M.id = :member_id
    INNER JOIN members as M ON M.animal_id = A.animal_id;"""

我有一个输入列表，例如：

animals_memberships = [
    {
        "animal_type": "BEAR",
        "member_id": 100,
    },
    {
        "animal_type": "RAT",
        "member_id": 200,
    },
    ...
]

目前，我正在遍历每个动物成员，并查询数据：

queries = []
for item in animals_memberships:
    session.execute(
        query, {
            "member_id": item["member_id"],
            "animal_type": item["animal_type"],
        }
    )

animal_names_foods = [
    result.fetchall()[0] for result in queries
]

是否可以进行“批量”查询，类似于使用 session.bulk_save_objects() 进行批量插入的方式？

【问题讨论】：

stackoverflow.com/questions/948212/…, stackoverflow.com/questions/9140015/…

标签： sql postgresql sqlalchemy

【解决方案1】：

您可以像这样在一个查询中获取所有数据

SELECT (A.name, A.food) FROM animals AS A
    WHERE
        (A.type, M.id) in (VALUES ('BEAR', 100), ('RAT', 200))
    INNER JOIN members as M ON M.animal_id = A.animal_id;

顺便问一下，如何在 python 中以安全的方式构建此查询

animals_memberships = [
    {
        "member_id": 100,
        "animal_type": "BEAR",
    },
    {
        "member_id": 200,
        "animal_type": "RAT",
    },
]

parts = []
params = {}

for idx, item in enumerate(animals_memberships):
    params[f"member_id_{idx}"] = item["member_id"]
    params[f"animal_type_{idx}"] = item["animal_type"]
    parts.append(f"(:member_id_{idx}, :animal_type_{idx})")

parts_str = ",".join(parts)

query = f"""
    SELECT (A.name, A.food) FROM animals AS A
    WHERE
        (A.type, M.id) IN (VALUES {parts_str})
    INNER JOIN members as M ON M.animal_id = A.animal_id;
"""

session.execute(query, params)

【讨论】：