如何在 SQLAlchemy ORM 中使用“as”选择查询并连接表

Question

我即将使用sqlalchemy 创建查询select join，例如：

SELECT position.*, device.name as devicename
FROM `position` JOIN `device`
ON position.id_device = device.id
ORDER BY position.id_device

所以在 python 文件中，我创建如下查询：

result = sql.query(Position, Device).\
            join(Device, Position.id_device == Device.id).\
            order_by(Position.id_device).first()

我得到了结果：

[
  {
    "id": 1,
    "size": "600x300",
    "price": 150,
    "id_category": 0,
    "id_device": 1,
    "impression": 9999,
    "status": 1,
    "name": "Home Top Banner",
    "id_website": 1
  },
  {
    "deleted_at": null,
    "status": 1,
    "name": "Desktop",
    "id": 1
  }
]

我想要的结果作为上面的mysql 查询是：

[
  {
    "id": 1,
    "size": "600x300",
    "price": 150,
    "id_category": 0,
    "id_device": 1,
    "impression": 9999,
    "status": 1,
    "name": "Home Top Banner",
    "id_website": 1,
    "devicename": "Desktop",
  }
]

主要代码流程：

[...]
engine = create_engine(SQLALCHEMY_DATABASE_URL)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
Base = declarative_base()
[...]

from sqlalchemy.orm import Session

def db_session() -> Generator:
    """
    Get database connection with DI (Dependencies Injection)
    """
    try:
        dbsession = SessionLocal()
        yield dbsession
    finally:
        dbsession.close()
    
@router.get('/{ad_type}')
def ad_unit(
        ad_type: str,
        sql: Session = Depends(db_session)
):
    """Display ads unit of the available product"""
    result = get_position(sql, ad_type=ad_type)
    return result
    [...]    

def get_position(sql: Session, ad_type: str):
    result = sql.query(Position, Device).\
              join(Device, Position.id_device == Device.id).\
              order_by(Position.id_device).first()
    [...]

模型类：

from sqlalchemy import Column
from sqlalchemy.dialects import mysql

from app.settings.mysql_settings import Base


class Position(Base):
    """A class used to represent position table (ads price list & dimensions)"""
    __tablename__ = 'position'

    id = Column(mysql.INTEGER(display_width=11, unsigned=True), primary_key=True,
                index=True, autoincrement=True)
    id_device = Column(mysql.INTEGER(display_width=11), nullable=True)
    id_website = Column(mysql.INTEGER(display_width=11), nullable=True)
    id_category = Column(mysql.INTEGER(display_width=11), nullable=True)
    name = Column(mysql.VARCHAR(length=50, collation="utf8_unicode_ci"), nullable=True)
    price = Column(mysql.INTEGER(display_width=11), nullable=True)
    status = Column(mysql.TINYINT(display_width=1), nullable=True, default=1)
    size = Column(mysql.TEXT(collation="utf8_unicode_ci"), nullable=True)
    impression = Column(mysql.DOUBLE(), nullable=False, default=0)


class Device(Base):
    """A class used to represent a list of device type for ads unit e.g: Mobile, Desktop, etc."""
    __tablename__ = 'device'

    id = Column(mysql.INTEGER(display_width=11), primary_key=True,
                index=True, autoincrement=True)
    name = Column(mysql.VARCHAR(length=50, collation="latin1_swedish_ci"), nullable=True)
    status = Column(mysql.TINYINT(display_width=1), nullable=True, default=1)
    deleted_at = Column(mysql.TIMESTAMP(), nullable=True)

我尝试了很多方法来获得我想要的结果，通过合并/联合结果和其他方法，但它不起作用。我认为有一种特定的方法可以通过sqlalchemy 获得我想要的结果，但我在文档中找不到它，因为参考资料太多了。

任何帮助将不胜感激，谢谢。

Answer 1

好吧，我终于找到了答案，我尝试了很多方法，你知道print 拯救我的一天：D

所以，我在这里找到了 2 个解决方案，这两个解决方案都像我想要的那样工作。第一个仍然使用 ORM 样式，第二个通过 raw 查询

j = join(Position, Device, Position.id_device == Device.id)
stmt = select([Position, Device.name.label('devicename')]).select_from(j)
result = sql.execute(stmt)
return result.fetchall()

# or by raw query
result = sql.execute("""SELECT position.*, device.name as devicename
    FROM `position`
    JOIN `device` on position.id_device = device.id
    ORDER BY position.id_device""")
return result.fetchall()

就是这样。谢谢大家的帮助。

Answer 2

翻译这样的查询：

SELECT users.name AS users_name,
        addresses_1.email_address AS addresses_1_email_address,
        addresses_2.email_address AS addresses_2_email_address
FROM users JOIN addresses AS addresses_1
        ON users.id = addresses_1.user_id
JOIN addresses AS addresses_2
        ON users.id = addresses_2.user_id
WHERE addresses_1.email_address = ?
        AND addresses_2.email_address = ?
('jack@google.com', 'j25@yahoo.com')

等效的 SQL 炼金术语法是这样的：

>>> from sqlalchemy.orm import aliased
>>> adalias1 = aliased(Address)
>>> adalias2 = aliased(Address)
SQL>>> for username, email1, email2 in \
...     session.query(User.name, adalias1.email_address, adalias2.email_address).\
...     join(User.addresses.of_type(adalias1)).\
...     join(User.addresses.of_type(adalias2)).\
...     filter(adalias1.email_address=='jack@google.com').\
...     filter(adalias2.email_address=='j25@yahoo.com'):
...     print(username, email1, email2)