使用 SqlAlchemy 代理到基于字典的集合时如何避免 IntegrityError

Question

使用 sqlalchemy 1.4.x，我设置了以下类：

from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm import declarative_base, sessionmaker
from sqlalchemy.orm.collections import attribute_mapped_collection
from sqlalchemy.orm import backref, relationship
from sqlalchemy import ForeignKey, Column, Integer, Unicode


from sqlalchemy import create_engine

engine = create_engine("sqlite:///:memory:", echo=True)
Session = sessionmaker(bind=engine)
session = Session()

Base = declarative_base()


class Infra(Base):

    __tablename__ = "infra"
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(Unicode(200), index=True, unique=True)
    protections = association_proxy(
        "infra_protections",
        "pscore",
        creator=lambda k, v: Infra_Protection(protection=k, pscore=v),
    )



class Protection(Base):

    __tablename__ = "protection"
    id = Column(Integer, primary_key=True, autoincrement=True)
    ptype = Column(Unicode(200), index=True, unique=True)

    def __init__(self, protection):
        self.ptype = protection


class Infra_Protection(Base):

    __tablename__ = "infraprotection"
    infra_id = Column(
        Integer, ForeignKey("infra.id", ondelete="CASCADE"), primary_key=True
    )
    protection_id = Column(
        Integer, ForeignKey("protection.id", ondelete="CASCADE"), primary_key=True
    )
    prot = relationship("Protection")
    protection = association_proxy("prot", "ptype")
    infra = relationship(
        Infra,
        backref=backref(
            "infra_protections",
            collection_class=attribute_mapped_collection("protection"),
            cascade="all, delete-orphan",
        ),
    )
    pscore = Column(Integer, nullable=False, unique=False, server_default="0")

现在我想添加一些 Infra 个对象，并关联 Protections:

Base.metadata.create_all(engine)
i = Infra(name="Foo")
i.protections["test"] = 1
i.protections["test 2"] = 2

session.add(i)
session.commit()

# now, add another
j = Infra(name="Bar")
j.protections["test"] = 3
j.protections["test 2"] = 4

session.add(j)
session.commit() # UNIQUE constraint failed: protection.ptype

很明显为什么 违反了唯一约束，但我想知道如何修改我的关联代理设置以合理稳健的方式避免这种情况。 Protection __init__?

上的某种 get_or_create

Answer 1

解决这个问题的方法是从这里实施一个 UniqueObject 配方：https://github.com/sqlalchemy/sqlalchemy/wiki/UniqueObject

使用 SqlAlchemy 代理到基于字典的集合时如何避免 IntegrityError

How to avoid IntegrityError when proxying to Dictionary-based collections using SqlAlchemy

python

sqlalchemy