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我有几个看起来像这样的简单模型：

class StoreImage(Base):
    imagepath = Column(Text, nullable=False)
    store_id = Column(Integer, ForeignKey('store.id'), nullable=False)
    store = relationship('Store')

class Store(Base):
    status = Column(Enum('published', 'verify', 'no_position',
                         name='store_status'),
                    nullable=False, default='verify')
    type = Column(Enum('physical', 'web', name='store_type'),
                  nullable=False, default='physical')
    name = Column(Text, nullable=False)
    street = Column(Text)
    postal_code = Column(Text)
    city = Column(Text)
    country = Column(Text)
    phone_number = Column(Text)
    email = Column(Text)
    website = Column(Text)
    location = Column(Geometry(geometry_type='POINT', srid=4326))
    is_flagship = Column(Boolean, default=False)
    images = relationship(StoreImage)

现在我想做的是这样的查询：

q = Store.query.filter(Store.is_flagship == True).with_entities(
    Store.id,
    Store.status,
    Store.slug,
    Store.type,
    Store.name,
    Store.street,
    Store.postal_code,
    Store.city,
    Store.country,
    Store.phone_number,
    Store.email,
    Store.website,
    func.ST_AsGeoJSON(Store.location).label('location'),
    Store.images,
)

查询有效，但Store.images只返回True每一行。如何让它返回StoreImage实例/KeyedTuples 列表？

我想这样做主要是因为我还没有找到任何其他方法来以Store.queryGeoJSON 格式返回位置。

编辑：对我来说，一种解决方案是从查询中返回Store实例并以某种方式添加locationGeoJSON，无论是在声明的模型上还是在可能的其他方式上。虽然不知道该怎么做。

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1 回答 1

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您当前的查询不仅返回错误的值，而且实际上返回错误的行数，因为它将执行两个表的笛卡尔积。
我也不会覆盖列名location。所以我将geo_location在下面的代码中使用。

你是对的，为了预加载图像，你必须查询整个Store实例。例如，像下面的查询：

q = (session.query(Store)
        .outerjoin(Store.images) # load images
        .options(contains_eager(Store.images)) # tell SA that we hav loaded them so that it will not perform another query
        .filter(Store.is_flagship == True)
    ).all()

为了将两者结合起来，您可以执行以下操作：

q = (session.query(Store, func.ST_AsGeoJSON(Store.location).label('geo_location'))
        .outerjoin(Store.images) # load images
        .options(contains_eager(Store.images)) # tell SA that we hav loaded them so that it will not perform another query
        .filter(Store.is_flagship == True)
    ).all()

# patch values in the instances of Store:
for store, geo_location in q:
    store.geo_location = geo_location

Edit-1：或者尝试使用column_property

class Store(...):
    # ...
    location_json = column_property(func.ST_AsGeoJSON(location).label('location_json'))

    q = (session.query(Store).label('geo_location'))
            .outerjoin(Store.images) # load images
            .options(contains_eager(Store.images)) # tell SA that we hav loaded them so that it will not perform another query
            .filter(Store.is_flagship == True)
        ).all()
    for store in q:
        print(q.location_json)
        print(len(q.images))
于 2014-08-07T09:47:53.327 回答