SQLAlchemy 将多对多连接表映射到键列表

Question

I have two tables with a many to many relationship:

purchase_order = Table(
    "purchase_order",
    metadata,
    Column("name", String, nullable=False, primary_key=True),
    ...
)

shipment = Table(
    "shipment",
    metadata,
    Column("identifier", String, nullable=False, primary_key=True),
)

shipment_po = Table(
    "shipment_po",
    metadata,
    Column(
        "shipment_identifier",
        String,
        ForeignKey("shipment.identifier"),
        nullable=False,
        primary_key=True,
    ),
    Column(
        "purchase_order_name",
        String,
        ForeignKey("purchase_order.name"),
        nullable=False,
        primary_key=True,
    ),
)

I'd like to map them to a class like this:

class Shipment:
    def __init__(
        self,
        identifier: str,
        purchase_order_names: list[str],
    ):
    ...

(Note that purchase_order_names is just a list of str, not a list of some PurchaseOrder object.)

So that I can create them like this (it being my responsibility to ensure the purchase_order rows here exist):

session.add(Shipment("my_shipment", purchase_order_names=["my_po_1", "my_po_2"]))

fetch like this:

session.query(Shipment).filter_by(identifier="my_shipment").one()

and update like this:

shipment.purchase_order_names.append("my_po_3")

Is this supported?

Answer 1

You can do this by adding a validator to Shipment that creates a PurchaseOrder from the provided name :

from sqlalchemy import orm

class Shipment:
    ...
    @orm.validates('purchase_orders')
    def validate_purchase_orders(self, key, purchase_order):
        return PurchaseOrder(name=purchase_order)

If you require more control you could create a custom collection class .