examples.dynamic_dict.dynamic_dict — SQLAlchemy 2.0 Documentation

Release: 2.0.49 | Release Date: April 3, 2026

# SQLAlchemy 2.0 Documentation

# Source code for examples.dynamic_dict.dynamic_dict

    from sqlalchemy import Column
    from sqlalchemy import create_engine
    from sqlalchemy import ForeignKey
    from sqlalchemy import Integer
    from sqlalchemy import String
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy.orm import relationship
    from sqlalchemy.orm import sessionmaker

    class ProxyDict:
        def __init__(self, parent, collection_name, childclass, keyname):
            self.parent = parent
            self.collection_name = collection_name
            self.childclass = childclass
            self.keyname = keyname

        @property
        def collection(self):
            return getattr(self.parent, self.collection_name)

        def keys(self):
            descriptor = getattr(self.childclass, self.keyname)
            return [x[0] for x in self.collection.values(descriptor)]

        def __getitem__(self, key):
            x = self.collection.filter_by(**{self.keyname: key}).first()
            if x:
                return x
            else:
                raise KeyError(key)

        def __setitem__(self, key, value):
            try:
                existing = self[key]
                self.collection.remove(existing)
            except KeyError:
                pass
            self.collection.append(value)

    engine = create_engine("sqlite://", echo=True)
    Base = declarative_base(engine)

    class Parent(Base):
        __tablename__ = "parent"
        id = Column(Integer, primary_key=True)
        name = Column(String(50))
        _collection = relationship(
            "Child", lazy="dynamic", cascade="all, delete-orphan"
        )

        @property
        def child_map(self):
            return ProxyDict(self, "_collection", Child, "key")

    class Child(Base):
        __tablename__ = "child"
        id = Column(Integer, primary_key=True)
        key = Column(String(50))
        parent_id = Column(Integer, ForeignKey("parent.id"))

        def __repr__(self):
            return "Child(key=%r)" % self.key

    Base.metadata.create_all()

    sess = sessionmaker()()

    p1 = Parent(name="p1")
    sess.add(p1)

    print("\n---------begin setting nodes, autoflush occurs\n")
    p1.child_map["k1"] = Child(key="k1")
    p1.child_map["k2"] = Child(key="k2")

    # this will autoflush the current map.
    # ['k1', 'k2']
    print("\n---------print keys - flushes first\n")
    print(list(p1.child_map.keys()))

    # k1
    print("\n---------print 'k1' node\n")
    print(p1.child_map["k1"])

    print("\n---------update 'k2' node - must find existing, and replace\n")
    p1.child_map["k2"] = Child(key="k2")

    print("\n---------print 'k2' key - flushes first\n")
    # k2
    print(p1.child_map["k2"])

    print("\n---------print all child nodes\n")
    # [k1, k2b]
    print(sess.query(Child).all())