[英]How to make SQLAlchemy insert work with Postgres multiprocessing-proof upsert trigger?
我有需要 upsert(插入,如果存在更新)功能的多處理應用程序。
我決定使用觸發器解決方案進行更新插入。 (您為名為 is_upsert 的每個啟用 upsert 的表添加額外的列,並在觸發器中檢查此字段,如果為 false,則執行正常插入,但如果為 true,則執行 upsert 邏輯 - 嘗試更新,如果失敗,因為記錄沒有'不存在你嘗試插入)。
這是觸發邏輯:
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;
測試對象,(add_upsert 只是讓上面的觸發器被安裝):
class SimpleItem(PipelinesBase):
__tablename__ = 'simple_item'
id = Column(BigInteger, primary_key=True)
item_type = Column(String, nullable=False, unique=True)
quantity = Column(Integer, nullable=False)
price = Column(Float, nullable=False)
in_stock = Column(Boolean, nullable=False)
arrived = Column(Date)
sys_time = Column(
TSTZRANGE,
nullable=False,
server_default=text("TSTZRANGE(now(), null)"),
)
_upsert = Column(Boolean, nullable=False, server_default=text('false'))
_type_identifier = 1400
add_upsert(SimpleItem, ['item_type'])
測試腳本
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()
使用 SQL 語句時它可以正常工作但是當我將它與 SQLAlchemy ORM 添加對象一起使用時
Traceback (most recent call last):
File "pipelines/persistence/experiment_with_upsert_field.py", line 59, in <module>
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 <listcomp>
for col, value in [
TypeError: 'NoneType' object is not subscriptable
提高 sqlalchemy.engine.default 的深度。 我很確定這是因為我的觸發器在執行 UPSERT 時返回 NULL 並且 SQLAlchemy 嘗試使用 RETURNING 語句傳播帶有插入 ID 的對象。 這顯然失敗了,因為不可能從它的從屬 INSERT/UPDATE 在觸發器中獲得正確的 ID,同時阻止正常的正常插入。
請注意,我已經將 upsert 測試為對我不起作用的特殊功能,因為我犧牲了 SQLAlchemy 對更新復雜項目(與其他項目有關系的項目)的幫助。
所以這是我的問題:如何告訴 SQLAlchemy 避免加載插入的對象 ID?
經過研究和測試,我發現它不能在 SQLAlchemy ORM 中完成。 然而,它可以在 SQLAlchemy Core 中通過將inline
關鍵字參數設置為 True 來完成:
engine.execute(
SimpleItem.__table__.insert(inline=True),
values
)
values['price'] = 1
engine.execute(
SimpleItem.__table__.insert(inline=True),
values
)
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