【发布时间】：2020-02-11 12:40:48
【问题描述】：
环境：
- python 3.7
- SqlAlchemy 1.3.10（我也在 1.2.16 上测试过，结果相同）
- PostgreSQL 11
TL,DR: 我有一个表和一个 1-1“相关”物化视图（没有 fk，关系在 sql 端是隐式的）。在 SQLAlchemy 中，这种关系被声明为viewonly=True。但是，如果我分配给它，会话无论如何都会尝试插入分配的 mat view 对象（显然，它失败了，因为它是一个物化视图）。
是我误解了viewonly的目的还是关系设置不正确？
完整的可重现测试用例：
- 使用 SQLalchemy 1.3.10 设置 python 3.7 venv
- 创建一个新的（空的）postgresql 数据库
- 将此代码示例保存在一个文件中，并将 DB_URI 值更改为您刚刚创建的值
- 在环境中执行文件 (
python <path-to-script>)
from __future__ import annotations
import unittest
from unittest import TestCase
import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base, DeclarativeMeta
from sqlalchemy.orm import relationship, backref, sessionmaker, object_session
create_sql = """
CREATE TABLE universe (
id SERIAL PRIMARY KEY,
name VARCHAR NOT NULL,
is_perfect BOOLEAN NULL DEFAULT 'f'
);
CREATE MATERIALIZED VIEW answer AS (
SELECT
id,
trunc(random() * 100)::INT AS computed
FROM universe
)
"""
Base: DeclarativeMeta = declarative_base()
metadata = Base.metadata
class Universe(Base):
__tablename__ = 'universe'
id = sa.Column(sa.Integer, primary_key=True)
name = sa.Column(sa.String, nullable=False)
is_perfect = sa.Column(sa.Boolean, nullable=False, server_default='f')
answer: Answer = relationship('Answer',
backref=backref('universe', uselist=False),
innerjoin=False,
lazy='select',
uselist=False,
viewonly=True)
def set_perfect(self):
self.is_perfect = (self.answer.computed == 42)
session = object_session(self)
if session:
session.commit()
class Answer(Base):
__tablename__ = 'answer'
id = sa.Column(sa.Integer, sa.ForeignKey('universe.id'), primary_key=True)
computed = sa.Column(sa.Integer, nullable=False)
DB_URI = 'postgresql://user:pass@localhost:5432/db_name' # Fill in your own
engine = sa.create_engine(DB_URI)
Session = sessionmaker(bind=engine, expire_on_commit=True)
session = Session()
class UniverseTests(TestCase):
def setUp(self) -> None:
session.execute("DROP MATERIALIZED VIEW IF EXISTS answer")
session.execute("DROP TABLE IF EXISTS universe")
session.execute(create_sql)
session.execute("INSERT INTO universe (id, name) VALUES (1, 'HG2G');")
session.commit()
def tearDown(self) -> None:
session.execute("DROP MATERIALIZED VIEW answer")
session.execute("DROP TABLE universe")
session.commit()
session.close()
def test__is_perfect(self):
universe: Universe = session.query(Universe).get(1)
universe.answer = Answer(id=1, computed=42)
universe.set_perfect()
assert universe.is_perfect is True
if __name__ == '__main__':
unittest.main()
如你所见，在测试过程中，我给universe.answer分配了一个假的Answer(id=1, computed=42)来测试方法.set_perfect()。
在set_perfect() 函数期间测试出错，因为对session.commit() 的调用尝试提交Answer(id=1, computed=42) 对象以及Universe 对象上的更新字段。
错误信息示例
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) cannot change materialized view "answer"
[SQL: INSERT INTO answer (id, computed) VALUES (%(id)s, %(computed)s)]
[parameters: {'id': 1, 'computed': 42}]
(Background on this error at: http://sqlalche.me/e/f405)
【问题讨论】：
标签： python postgresql sqlalchemy materialized-views