fix(141): handle after_flush_postexec when creating version objects

when creating version objects if a person has created after_flush_postexec
hook, which keeps calling `after_flush` untill it exhausts 100 attempts
or session is no longer dirty, this is picked up by mapper as after_update
which within same transaction adds a update operation type, so we have a
check if target is already in UoW we continue with operation type that
it is in untill transaction is completed.

sqlalchemy_history/operation.py

@@ -90,7 +90,11 @@ def add_update(self, target):
                     del state_copy[rel_key]
 
         if state_copy:
-            self.add(Operation(target, Operation.UPDATE))
-
+            if target in self:
+                # If already in current transaction and some event hook did a update
+                # prior to commit hook, continue with operation type as it is
+                self.add(Operation(target, self[self.format_key(target)].type))
+            else:
+                self.add(Operation(target, Operation.UPDATE))
     def add_delete(self, target):
         self.add(Operation(target, Operation.DELETE))

tests/reported_bugs/test_bug_141_after_flush_postexec_op_type_issue.py

@@ -0,0 +1,76 @@
+import datetime
+import sqlalchemy as sa
+from copy import copy
+
+from tests import TestCase
+from sqlalchemy_history import version_class
+
+
+class TestBug141(TestCase):
+    # ref: https://github.com/corridor/sqlalchemy-history/issues/141
+    def create_models(self):
+        article_author_table = sa.Table(
+            "article_author",
+            self.Model.metadata,
+            sa.Column(
+                "article_id", sa.Integer, sa.ForeignKey("article.id"), primary_key=True, nullable=False
+            ),
+            sa.Column("author_id", sa.Integer, sa.ForeignKey("author.id"), primary_key=True, nullable=False),
+            sa.Column(
+                "created_date",
+                sa.DateTime,
+                nullable=False,
+                server_default=sa.func.current_timestamp(),
+                default=lambda: datetime.datetime.now(datetime.timezone.utc)
+            ),
+        )
+
+        class Article(self.Model):
+            __tablename__ = "article"
+            __versioned__ = copy(self.options)
+
+            id = sa.Column(
+                sa.Integer, sa.Sequence(f"{__tablename__}_seq", start=1), autoincrement=True, primary_key=True
+            )
+            name = sa.Column(sa.Unicode(255), nullable=False)
+            content = sa.Column(sa.UnicodeText)
+
+        class Author(self.Model):
+            __tablename__ = "author"
+            __versioned__ = copy(self.options)
+
+            id = sa.Column(
+                sa.Integer, sa.Sequence(f"{__tablename__}_seq", start=1), autoincrement=True, primary_key=True
+            )
+            name = sa.Column(sa.Unicode(255))
+            article_id = sa.Column(sa.Integer, sa.ForeignKey(Article.id))
+            articles = sa.orm.relationship(Article, secondary=article_author_table, backref="authors")
+
+        self.Article = Article
+        self.Author = Author
+        self.article_author_table = article_author_table
+
+    def test_add_record(self):
+        article = self.Article(name="Article 1")
+        author = self.Author(name="Author 1", articles=[article])
+        @sa.event.listens_for(self.session, 'after_flush_postexec')
+        def after_flush_postexec(session, flush_context):
+            if author.name != "yoyoyoyoyo":
+                author.name = "yoyoyoyoyo"
+        self.session.add(article)
+        self.session.add(author)
+        self.session.commit()
+
+        versioned_objs = self.session.query(version_class(self.Author)).all()
+        assert len(versioned_objs) == 1
+        assert versioned_objs[0].operation_type == 0
+        assert versioned_objs[0].name == "yoyoyoyoyo"
+        author.name = "sdfeoinfe"
+        self.session.add(author)
+        self.session.commit()
+        versioned_objs = self.session.query(version_class(self.Author)).all()
+        assert len(versioned_objs) == 2
+        assert versioned_objs[0].operation_type == 0
+        assert versioned_objs[1].operation_type == 1
+        assert versioned_objs[0].name == versioned_objs[1].name == "yoyoyoyoyo"
+        sa.event.remove(self.session, "after_flush_postexec", after_flush_postexec)