sqlalchemy 使用经典映射将整个表映射为属性

Question

给定以下类和数据库表

class Location:
    datacenter_name: str
    path: str

locations = Table(
    "locations",
    mapper_registry.metadata,
    Column("id", Integer, primary_key=True, autoincrement=True),
    Column("path", String, nullable=False),
    Column("datacenter_name", String, nullable=False),
)
mapper_registry.map_imperatively(Location, locations)

backup_registry = Table(
    "backup_registry",
    mapper_registry.metadata,
    Column("id", Integer, primary_key=True, autoincrement=True),
    Column("source_location_id", ForeignKey("locations.id"), nullable=False),
    Column("backup_location_id", ForeignKey("locations.id"), nullable=False),
)

我想将 backup_registry 表映射到 BackupRegistry 实例，但我需要 将所有行映射到单个属性，例如：

class BackupRegistry:
    backups: Dict[Location, list[Location]]

使用与 location 相同的方法会给我一个 BackupRegistry 实例 每行mapper_registry.map_imperatively(BackupRegistry, backup_registry)

对如何通过经典映射实现这一点有任何想法吗？

Answer 1

我不确定这种关系的内置解决方案是否不起作用或只是埋在文档中。

class Location:
    pass


locations = Table(
    "locations",
    mapper_registry.metadata,
    Column("id", Integer, primary_key=True, autoincrement=True),
    Column("path", String, nullable=False),
    Column("datacenter_name", String, nullable=False),
)

backup_registry = Table(
    "backup_registry",
    mapper_registry.metadata,
    Column("id", Integer, primary_key=True, autoincrement=True),
    Column("source_location_id", ForeignKey("locations.id"), nullable=False),
    Column("backup_location_id", ForeignKey("locations.id"), nullable=False),
)

mapper_registry.map_imperatively(Location, locations, properties={
    'backup_locations': relationship(Location,
                                     primaryjoin=locations.c.id == backup_registry.c.source_location_id,
                                     secondary=backup_registry,
                                     secondaryjoin=locations.c.id == backup_registry.c.backup_location_id,
                                     backref='source_locations',
    ),
})

然后可以从Location 访问backup_locations，例如location.backup_locations，这将是list() 的Locations。

这在self-referential-many-to-many-relationship 的文档中有记录。