1 files changed, 105 insertions, 0 deletions
diff --git a/examples/versioned_rows/versioned_rows.py b/examples/versioned_rows/versioned_rows.py
new file mode 100644
index 000000000..30acf4e0d
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+++ b/examples/versioned_rows/versioned_rows.py
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+"""Illustrates a method to intercept changes on objects, turning
+an UPDATE statement on a single row into an INSERT statement, so that a new
+row is inserted with the new data, keeping the old row intact.
+
+"""
+from sqlalchemy.orm import *
+from sqlalchemy import *
+from sqlalchemy.orm.interfaces import SessionExtension
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import attributes
+
+class Versioned(object):
+    def new_version(self, session):
+        # if on SQLA 0.6.1 or earlier,
+        # make sure 'id' isn't expired.
+        # self.id
+
+        # make us transient (removes persistent
+        # identity).
+        make_transient(self)
+
+        # set 'id' to None.
+        # a new PK will be generated on INSERT.
+        self.id = None
+
+class VersionExtension(SessionExtension):
+    def before_flush(self, session, flush_context, instances):
+        for instance in session.dirty:
+            if not isinstance(instance, Versioned):
+                continue
+            if not session.is_modified(instance, passive=True):
+                continue
+
+            if not attributes.instance_state(instance).has_identity:
+                continue
+
+            # make it transient
+            instance.new_version(session)
+            # re-add
+            session.add(instance)
+
+Base = declarative_base()
+
+engine = create_engine('sqlite://', echo=True)
+
+Session = sessionmaker(engine, extension=[VersionExtension()])
+
+# example 1, simple versioning
+
+class Example(Versioned, Base):
+    __tablename__ = 'example'
+    id = Column(Integer, primary_key=True)
+    data = Column(String)
+
+Base.metadata.create_all(engine)
+
+session = Session()
+e1 = Example(data='e1')
+session.add(e1)
+session.commit()
+
+e1.data = 'e2'
+session.commit()
+
+assert session.query(Example.id, Example.data).order_by(Example.id).all() == \
+        [(1, 'e1'), (2, 'e2')]
+
+# example 2, versioning with a parent
+
+class Parent(Base):
+    __tablename__ = 'parent'
+    id = Column(Integer, primary_key=True)
+    child_id = Column(Integer, ForeignKey('child.id'))
+    child = relationship("Child", backref=backref('parent', uselist=False))
+
+class Child(Versioned, Base):
+    __tablename__ = 'child'
+
+    id = Column(Integer, primary_key=True)
+    data = Column(String)
+
+    def new_version(self, session):
+        # expire parent's reference to us
+        session.expire(self.parent, ['child'])
+
+        # create new version
+        Versioned.new_version(self, session)
+
+        # re-add ourselves to the parent
+        self.parent.child = self
+
+Base.metadata.create_all(engine)
+
+session = Session()
+
+p1 = Parent(child=Child(data='c1'))
+session.add(p1)
+session.commit()
+
+p1.child.data = 'c2'
+session.commit()
+
+assert p1.child_id == 2
+assert session.query(Child.id, Child.data).order_by(Child.id).all() == \
+    [(1, 'c1'), (2, 'c2')]
+\ No newline at end of file