[SQLAlchemy] Synchronize_session parameter detailed

The synchronize_session is used for query synchronization policy for the session when the delete or update operation is performed.

• False-Do not synchronize the session with the delete or update operation directly.
• ' Fetch '

Before the delete or update operation, send a SQL to the database to get the records that match the criteria.

1 def_do_pre_synchronize (self):2query =Self.query3Session =query.session4Context =Query._compile_context ()5SELECT_STMT =Context.statement.with_only_columns (6 Self.primary_table.primary_key)7Self.matched_rows =Session.execute (8 select_stmt,9Mapper=Self.mapper,TenParams=query._params). Fetchall ()

After the delete or update operation, match the Identity_map of the session with the record obtained in the previous step, and the qualifying entries are deleted or updated from the session.

1 def_do_post_synchronize (self):2Session =self.query.session3Target_mapper =Self.query._mapper_zero ()4          forPrimary_keyinchself.matched_rows:5             #Todo:inline This and the call remove_newly_deleted6             #once7Identity_key =Target_mapper.identity_key_from_primary_key (8 list (primary_key))9             ifIdentity_keyinchSession.identity_map:Ten session._remove_newly_deleted ( One [Attributes.instance_state ( A Session.identity_map[identity_key] -                     )] -)

• ' Evaluate '

Before the delete or update operation, the objects in the session's Identity_map is directly eval with the conditions in query, and the qualifying record is recorded.

1 def_do_pre_synchronize (self):2query =Self.query3Target_cls =Query._mapper_zero (). Class_4 5         Try:6Evaluator_compiler =evaluator. Evaluatorcompiler (TARGET_CLS)7             ifQuery.whereclause is  notNone:8Eval_condition =evaluator_compiler.process (9 query.whereclause)Ten             Else: One                 defeval_condition (obj): A                     returnTrue -  - self._additional_evaluators (Evaluator_compiler) the  -         exceptevaluator. Unevaluatableerror: -             RaiseSa_exc. Invalidrequesterror ( -                 "Could not evaluate current criteria in Python." +                 "specify ' fetch ' or False for the" -                 "synchronize_session parameter.") +  A         #Todo:detect when the WHERE clause is a trivial primary key match atSelf.matched_objects = [ -Obj for(CLS, PK), objinch - Query.session.identity_map.items () -             ifIssubclass (CLS, TARGET_CLS) and -Eval_condition (obj)]

After the delete or update operation, the eligible records are deleted or updated.

1 def _do_post_synchronize (self): 2         self.query.session._remove_newly_deleted (3            [Attributes.instance_state (obj)  4for in               self.matched_objects])

[SQLAlchemy] Synchronize_session parameter detailed