我有多处理应用程序，需要upsert(插入，如果存在更新)功能。在

我决定使用触发器解决方案来接近upsert。(为每个名为is_upsert的启用upsert的表添加额外的列，在触发器检查此字段时，如果为false，则执行正常插入，但如果为true，则执行upsert逻辑-尝试更新，如果由于记录不存在而失败，则尝试插入)。在

触发逻辑如下：CREATE OR REPLACE FUNCTION upsert_trigger_function_{table}()

RETURNS TRIGGER AS $upsert_trigger_function$

DECLARE

row record;

BEGIN

RAISE NOTICE 'upsert trigger fired, upsert is %%', NEW.{upsert_column};

IF NEW.{upsert_column} THEN

NEW.{upsert_column} := false;

LOOP

UPDATE {table} SET

{update_set}

WHERE

{update_where}

;

IF found THEN

RETURN NULL;

END IF;

BEGIN

INSERT INTO {table} SELECT NEW.*;

RETURN NULL;

EXCEPTION WHEN unique_violation THEN

-- loop

END;

END LOOP;

RETURN NULL;

ELSE

RETURN NEW;

END IF;

END;

$upsert_trigger_function$ LANGUAGE plpgsql;

测试对象(add\u upsert只需安装上述触发器)：

^{pr2}$

测试脚本from sqlalchemy.engine import create_engine

from pipelines.settings_proxy import TEST_DB

from sqlalchemy.orm.session import sessionmaker

from test_pipelines.test_persistence.mock_items import SimpleItem

from test_pipelines.test_persistence.helpers import random_simple_item

def main():

engine = create_engine(TEST_DB)

values = random_simple_item(_upsert=True)

session = sessionmaker(engine)()

si = SimpleItem(**values)

session.add(si)

session.commit()

si = SimpleItem(**values)

si.price = 1

session.merge(si)

session.commit()

它在使用SQL statesments时可以正常工作，但是当我将它与SQLAlchemy ORM add object一起使用时，它就有了Traceback (most recent call last):

File "pipelines/persistence/experiment_with_upsert_field.py", line 59, in

main()

File "pipelines/persistence/experiment_with_upsert_field.py", line 27, in main

session.commit()

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 801, in commit

self.transaction.commit()

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 392, in commit

self._prepare_impl()

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 372, in _prepare_impl

self.session.flush()

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 2019, in flush

self._flush(objects)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 2137, in _flush

transaction.rollback(_capture_exception=True)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__

compat.reraise(exc_type, exc_value, exc_tb)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/util/compat.py", line 184, in reraise

raise value

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 2101, in _flush

flush_context.execute()

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/unitofwork.py", line 373, in execute

rec.execute(self)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/unitofwork.py", line 532, in execute

uow

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/persistence.py", line 174, in save_obj

mapper, table, insert)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/orm/persistence.py", line 800, in _emit_insert_statements

execute(statement, params)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 914, in execute

return meth(self, multiparams, params)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/sql/elements.py", line 323, in _execute_on_connection

return connection._execute_clauseelement(self, multiparams, params)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1010, in _execute_clauseelement

compiled_sql, distilled_params

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1159, in _execute_context

result = context._setup_crud_result_proxy()

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/engine/default.py", line 828, in _setup_crud_result_proxy

self._setup_ins_pk_from_implicit_returning(row)

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/engine/default.py", line 893, in _setup_ins_pk_from_implicit_returning

for col in table.primary_key

File "/home/sebastian/local/virtualenvs/perception/lib/python3.4/site-packages/sqlalchemy/engine/default.py", line 891, in

for col, value in [

TypeError: 'NoneType' object is not subscriptable

在深处升起sqlalchemy.engine.default. 我确信这是因为我的触发器在执行UPSERT时返回NULL，而SQLAlchemy尝试使用RETURNING语句传播带有插入ID的对象。它显然失败了，因为它不可能从它的从属INSERT/UPDATE在触发器中获取正确的ID，同时阻止正常的正常插入。在

请注意，我已经将upsert作为一个特殊函数进行了测试，但这对我来说并不适用，因为我牺牲了SQLAlchemy在更新复杂项(那些与其他项有关系的项)方面的帮助。在

所以我的问题是：如何告诉SQLAlchemy避免加载插入的对象ID？