SQLAlchemy Essential: Chapter 3
This commit is contained in:
Pavel Vavilin
@@ -1523,3 +1523,746 @@
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#+RESULTS:
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| 1 | cookiemon | 111-111-1111 | chocolate chip | 2 | Decimal | (1.00) |
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| 1 | cookiemon | 111-111-1111 | ligth chocolate chip | 12 | Decimal | (3.00) |
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* Chapter 3: Exceptions and Transactions
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** SQLAlchemy v1
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:PROPERTIES:
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:header-args: :cache no
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:header-args:python: :tangle ch3-v1.py
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:header-args: :session *ch3*
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:END:
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#+BEGIN_SRC python :shebang "#!/usr/bin/env python3" :results none
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import sys
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sys.stderr = sys.stdout
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from datetime import datetime
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from sqlalchemy import (
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Boolean,
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CheckConstraint,
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Column,
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DateTime,
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ForeignKey,
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Integer,
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MetaData,
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Numeric,
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String,
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Table,
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create_engine,
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PrimaryKeyConstraint,
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UniqueConstraint,
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)
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from sqlparse import format as sqlformat
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def sqlf(
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sql: str | object,
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reindent=True,
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keyword_case="upper",
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indent_width=2,
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strip_comments=False,
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identifier_case="lower",
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):
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if not isinstance(sql, str):
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sql = str(sql)
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return sqlformat(
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sql,
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encoding="utf8",
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reindent=reindent,
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keyword_case=keyword_case,
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indent_width=indent_width,
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strip_comments=strip_comments,
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identifier_case=identifier_case,
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)
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metadata = MetaData()
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cookies = Table(
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"cookies",
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metadata,
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Column("cookie_id", Integer(), primary_key=True),
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Column("cookie_name", String(50), index=True),
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Column("cookie_recipe_url", String(255), unique=True),
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Column("cookie_sku", String(55), unique=True),
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Column("quantity", Integer()),
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Column("unit_cost", Numeric(12, 2)),
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CheckConstraint("unit_cost >= 0.00", name="unit_cost_positive"),
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CheckConstraint("quantity >= 0", name="quantity_positive"),
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)
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users = Table(
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"users",
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metadata,
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Column("user_id", Integer()),
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Column("username", String(15), nullable=False),
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Column("email_address", String(255), nullable=False),
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Column("phone", String(20), nullable=False),
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Column("password", String(25), nullable=False),
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Column("created_on", DateTime(), default=datetime.now),
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Column("updated_on", DateTime(), default=datetime.now, onupdate=datetime.now),
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PrimaryKeyConstraint("user_id", name="user_pk"),
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UniqueConstraint("username", name="uix_username"),
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)
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orders = Table(
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"orders",
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metadata,
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Column("order_id", Integer(), primary_key=True),
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Column("user_id", ForeignKey("users.user_id")),
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Column("shipped", Boolean(), default=False),
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)
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line_items = Table(
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"line_items",
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metadata,
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Column("line_items_id", Integer(), primary_key=True),
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Column("order_id", ForeignKey("orders.order_id")),
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Column("cookie_id", ForeignKey("cookies.cookie_id")),
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Column("quantity", Integer()),
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Column("extended_cost", Numeric(12, 2)),
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)
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engine = create_engine("sqlite:///:memory:", echo=True)
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connection = engine.connect()
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metadata.create_all(engine)
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#+END_SRC
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*** AttributeError
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#+BEGIN_SRC python :results output
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import logging
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from sqlalchemy import select, insert
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ins = insert(users).values(
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username="cookiemon",
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email_address="mon@cookie.com",
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phone="111-111-1111",
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password="password",
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)
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result = connection.execute(ins)
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s = select(users.c.username)
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results = connection.execute(s)
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try:
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[(result.username, result.password) for result in results]
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except AttributeError as exc:
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logging.exception(results)
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#+END_SRC
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#+RESULTS:
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#+begin_example
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2026-09-18 12:06:22,953 INFO sqlalchemy.engine.Engine BEGIN (implicit)
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INFO:sqlalchemy.engine.Engine:BEGIN (implicit)
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2026-09-18 12:06:22,954 INFO sqlalchemy.engine.Engine INSERT INTO users (username, email_address, phone, password, created_on, updated_on) VALUES (?, ?, ?, ?, ?, ?)
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INFO:sqlalchemy.engine.Engine:INSERT INTO users (username, email_address, phone, password, created_on, updated_on) VALUES (?, ?, ?, ?, ?, ?)
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2026-09-18 12:06:22,954 INFO sqlalchemy.engine.Engine [generated in 0.00036s] ('cookiemon', 'mon@cookie.com', '111-111-1111', 'password', '2026-09-18 12:06:22.953895', '2026-09-18 12:06:22.953904')
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INFO:sqlalchemy.engine.Engine:[generated in 0.00036s] ('cookiemon', 'mon@cookie.com', '111-111-1111', 'password', '2026-09-18 12:06:22.953895', '2026-09-18 12:06:22.953904')
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2026-09-18 12:06:22,954 INFO sqlalchemy.engine.Engine SELECT users.username
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FROM users
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INFO:sqlalchemy.engine.Engine:SELECT users.username
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FROM users
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2026-09-18 12:06:22,954 INFO sqlalchemy.engine.Engine [generated in 0.00014s] ()
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INFO:sqlalchemy.engine.Engine:[generated in 0.00014s] ()
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ERROR:root:<sqlalchemy.engine.cursor.CursorResult object at 0x7fa8f6747950>
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Traceback (most recent call last):
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/result.py", line 211, in _key_not_found
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self._key_fallback(key, None)
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~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/cursor.py", line 851, in _key_fallback
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raise exc.NoSuchColumnError(
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...<2 lines>...
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) from err
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sqlalchemy.exc.NoSuchColumnError: Could not locate column in row for column 'password'
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The above exception was the direct cause of the following exception:
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Traceback (most recent call last):
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File "/tmp/babel-sg4Ps9/python-VQah8h", line 17, in <module>
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[(result.username, result.password) for result in results]
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^^^^^^^^^^^^^^^
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File "lib/sqlalchemy/cyextension/resultproxy.pyx", line 66, in sqlalchemy.cyextension.resultproxy.BaseRow.__getattr__
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File "lib/sqlalchemy/cyextension/resultproxy.pyx", line 63, in sqlalchemy.cyextension.resultproxy.BaseRow._get_by_key_impl
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/result.py", line 213, in _key_not_found
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raise AttributeError(ke.args[0]) from ke
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AttributeError: Could not locate column in row for column 'password'
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#+end_example
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*** IntegrityError
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#+BEGIN_SRC python :results output
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from sqlalchemy.exc import IntegrityError
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s = select(users.c.username)
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print(connection.execute(s).fetchall())
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ins = insert(users).values(
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username="cookiemon",
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email_address="damon@cookie.com",
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phone="111-111-1111",
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password="password",
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)
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try:
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result = connection.execute(ins)
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except IntegrityError as exc:
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logging.exception(str(ins))
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#+END_SRC
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#+RESULTS[cdbcb9c1f18b5c62c2127f1ac9ffd14b2a38039e]:
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#+begin_example
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2026-09-18 12:06:22,969 INFO sqlalchemy.engine.Engine SELECT users.username
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FROM users
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INFO:sqlalchemy.engine.Engine:SELECT users.username
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FROM users
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2026-09-18 12:06:22,969 INFO sqlalchemy.engine.Engine [cached since 0.01439s ago] ()
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INFO:sqlalchemy.engine.Engine:[cached since 0.01439s ago] ()
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[('cookiemon',)]
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2026-09-18 12:06:22,969 INFO sqlalchemy.engine.Engine INSERT INTO users (username, email_address, phone, password, created_on, updated_on) VALUES (?, ?, ?, ?, ?, ?)
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INFO:sqlalchemy.engine.Engine:INSERT INTO users (username, email_address, phone, password, created_on, updated_on) VALUES (?, ?, ?, ?, ?, ?)
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2026-09-18 12:06:22,969 INFO sqlalchemy.engine.Engine [cached since 0.0159s ago] ('cookiemon', 'damon@cookie.com', '111-111-1111', 'password', '2026-09-18 12:06:22.969623', '2026-09-18 12:06:22.969627')
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INFO:sqlalchemy.engine.Engine:[cached since 0.0159s ago] ('cookiemon', 'damon@cookie.com', '111-111-1111', 'password', '2026-09-18 12:06:22.969623', '2026-09-18 12:06:22.969627')
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ERROR:root:INSERT INTO users (username, email_address, phone, password, created_on, updated_on) VALUES (:username, :email_address, :phone, :password, :created_on, :updated_on)
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Traceback (most recent call last):
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1969, in _exec_single_context
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self.dialect.do_execute(
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~~~~~~~~~~~~~~~~~~~~~~~^
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cursor, str_statement, effective_parameters, context
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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)
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^
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/default.py", line 952, in do_execute
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cursor.execute(statement, parameters)
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~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
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sqlite3.IntegrityError: UNIQUE constraint failed: users.username
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The above exception was the direct cause of the following exception:
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Traceback (most recent call last):
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File "/tmp/babel-sg4Ps9/python-Dqwfvm", line 13, in <module>
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result = connection.execute(ins)
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1421, in execute
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return meth(
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self,
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distilled_parameters,
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execution_options or NO_OPTIONS,
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)
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/sql/elements.py", line 526, in _execute_on_connection
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return connection._execute_clauseelement(
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
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self, distilled_params, execution_options
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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)
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^
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1643, in _execute_clauseelement
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ret = self._execute_context(
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dialect,
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...<8 lines>...
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cache_hit=cache_hit,
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)
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1848, in _execute_context
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return self._exec_single_context(
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~~~~~~~~~~~~~~~~~~~~~~~~~^
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dialect, context, statement, parameters
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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)
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^
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1988, in _exec_single_context
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self._handle_dbapi_exception(
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
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e, str_statement, effective_parameters, cursor, context
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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)
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^
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 2365, in _handle_dbapi_exception
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raise sqlalchemy_exception.with_traceback(exc_info[2]) from e
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1969, in _exec_single_context
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self.dialect.do_execute(
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~~~~~~~~~~~~~~~~~~~~~~~^
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cursor, str_statement, effective_parameters, context
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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)
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^
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File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/default.py", line 952, in do_execute
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cursor.execute(statement, parameters)
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~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
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sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE constraint failed: users.username
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[SQL: INSERT INTO users (username, email_address, phone, password, created_on, updated_on) VALUES (?, ?, ?, ?, ?, ?)]
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[parameters: ('cookiemon', 'damon@cookie.com', '111-111-1111', 'password', '2026-09-18 12:06:22.969623', '2026-09-18 12:06:22.969627')]
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(Background on this error at: https://sqlalche.me/e/20/gkpj)
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#+end_example
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*** Transactions
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#+BEGIN_SRC python :results none
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ins = cookies.insert()
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inventory_list = [
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{
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"cookie_name": "chocolate chip",
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"cookie_recipe_url": "http://some.aweso.me/cookie/recipe.html",
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"cookie_sku": "CC01",
|
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"quantity": "12",
|
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"unit_cost": "0.5",
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},
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{
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"cookie_name": "dark chocolate chip",
|
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"cookie_recipe_url": "http://some.aweso.me/cookie/recipe_dark.html",
|
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"cookie_sku": "CC02",
|
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"quantity": "1",
|
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"unit_cost": "0.75",
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},
|
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]
|
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result = connection.execute(ins, inventory_list)
|
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#+END_SRC
|
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|
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#+BEGIN_SRC python :results none
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ins = insert(orders).values(user_id=1, order_id="1")
|
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result = connection.execute(ins)
|
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ins = insert(line_items)
|
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order_items = [
|
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{
|
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"order_id": 1,
|
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"cookie_id": 1,
|
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"quantity": 9,
|
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"extended_cost": 4.50,
|
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}
|
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]
|
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result = connection.execute(ins, order_items)
|
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|
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ins = insert(orders).values(user_id=1, order_id="2")
|
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result = connection.execute(ins)
|
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ins = insert(line_items)
|
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order_items = [
|
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{
|
||||
"order_id": 2,
|
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"cookie_id": 1,
|
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"quantity": 4,
|
||||
"extended_cost": 1.50,
|
||||
},
|
||||
{
|
||||
"order_id": 2,
|
||||
"cookie_id": 2,
|
||||
"quantity": 1,
|
||||
"extended_cost": 4.50,
|
||||
},
|
||||
]
|
||||
result = connection.execute(ins, order_items)
|
||||
#+END_SRC
|
||||
|
||||
#+BEGIN_SRC python :results none
|
||||
from sqlalchemy import update
|
||||
|
||||
|
||||
def ship_it(order_id: int) -> None:
|
||||
s = select(line_items.c.cookie_id, line_items.c.quantity)
|
||||
s = s.where(line_items.c.order_id == order_id)
|
||||
cookies_to_ship = connection.execute(s)
|
||||
for cookie in cookies_to_ship:
|
||||
u = (
|
||||
update(cookies)
|
||||
.where(cookies.c.cookie_id == cookie.cookie_id)
|
||||
.values(quantity=cookies.c.quantity - cookie.quantity)
|
||||
)
|
||||
result = connection.execute(u)
|
||||
u = update(orders).where(orders.c.order_id == order_id).values(shipped=True)
|
||||
connection.execute(u)
|
||||
print(f"Shipped order ID: {order_id}")
|
||||
#+END_SRC
|
||||
|
||||
#+BEGIN_SRC python :results output
|
||||
ship_it(1)
|
||||
s = select(cookies.c.cookie_name, cookies.c.quantity)
|
||||
print(connection.execute(s).fetchall())
|
||||
#+END_SRC
|
||||
|
||||
#+RESULTS:
|
||||
#+begin_example
|
||||
2026-09-18 12:06:23,066 INFO sqlalchemy.engine.Engine SELECT line_items.cookie_id, line_items.quantity
|
||||
FROM line_items
|
||||
WHERE line_items.order_id = ?
|
||||
INFO:sqlalchemy.engine.Engine:SELECT line_items.cookie_id, line_items.quantity
|
||||
FROM line_items
|
||||
WHERE line_items.order_id = ?
|
||||
2026-09-18 12:06:23,066 INFO sqlalchemy.engine.Engine [generated in 0.00024s] (1,)
|
||||
INFO:sqlalchemy.engine.Engine:[generated in 0.00024s] (1,)
|
||||
2026-09-18 12:06:23,067 INFO sqlalchemy.engine.Engine UPDATE cookies SET quantity=(cookies.quantity - ?) WHERE cookies.cookie_id = ?
|
||||
INFO:sqlalchemy.engine.Engine:UPDATE cookies SET quantity=(cookies.quantity - ?) WHERE cookies.cookie_id = ?
|
||||
2026-09-18 12:06:23,067 INFO sqlalchemy.engine.Engine [generated in 0.00009s] (9, 1)
|
||||
INFO:sqlalchemy.engine.Engine:[generated in 0.00009s] (9, 1)
|
||||
2026-09-18 12:06:23,067 INFO sqlalchemy.engine.Engine UPDATE orders SET shipped=? WHERE orders.order_id = ?
|
||||
INFO:sqlalchemy.engine.Engine:UPDATE orders SET shipped=? WHERE orders.order_id = ?
|
||||
2026-09-18 12:06:23,067 INFO sqlalchemy.engine.Engine [generated in 0.00008s] (1, 1)
|
||||
INFO:sqlalchemy.engine.Engine:[generated in 0.00008s] (1, 1)
|
||||
Shipped order ID: 1
|
||||
2026-09-18 12:06:23,067 INFO sqlalchemy.engine.Engine SELECT cookies.cookie_name, cookies.quantity
|
||||
FROM cookies
|
||||
INFO:sqlalchemy.engine.Engine:SELECT cookies.cookie_name, cookies.quantity
|
||||
FROM cookies
|
||||
2026-09-18 12:06:23,067 INFO sqlalchemy.engine.Engine [generated in 0.00006s] ()
|
||||
INFO:sqlalchemy.engine.Engine:[generated in 0.00006s] ()
|
||||
[('chocolate chip', 3), ('dark chocolate chip', 1)]
|
||||
#+end_example
|
||||
|
||||
#+BEGIN_SRC python :results output
|
||||
try:
|
||||
ship_it(2)
|
||||
except IntegrityError:
|
||||
logging.exception("")
|
||||
#+END_SRC
|
||||
|
||||
#+RESULTS:
|
||||
#+begin_example
|
||||
2026-09-18 12:07:29,522 INFO sqlalchemy.engine.Engine SELECT line_items.cookie_id, line_items.quantity
|
||||
FROM line_items
|
||||
WHERE line_items.order_id = ?
|
||||
INFO:sqlalchemy.engine.Engine:SELECT line_items.cookie_id, line_items.quantity
|
||||
FROM line_items
|
||||
WHERE line_items.order_id = ?
|
||||
2026-09-18 12:07:29,522 INFO sqlalchemy.engine.Engine [cached since 66.46s ago] (2,)
|
||||
INFO:sqlalchemy.engine.Engine:[cached since 66.46s ago] (2,)
|
||||
2026-09-18 12:07:29,523 INFO sqlalchemy.engine.Engine UPDATE cookies SET quantity=(cookies.quantity - ?) WHERE cookies.cookie_id = ?
|
||||
INFO:sqlalchemy.engine.Engine:UPDATE cookies SET quantity=(cookies.quantity - ?) WHERE cookies.cookie_id = ?
|
||||
2026-09-18 12:07:29,523 INFO sqlalchemy.engine.Engine [cached since 66.46s ago] (4, 1)
|
||||
INFO:sqlalchemy.engine.Engine:[cached since 66.46s ago] (4, 1)
|
||||
ERROR:root:
|
||||
Traceback (most recent call last):
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1969, in _exec_single_context
|
||||
self.dialect.do_execute(
|
||||
~~~~~~~~~~~~~~~~~~~~~~~^
|
||||
cursor, str_statement, effective_parameters, context
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
)
|
||||
^
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/default.py", line 952, in do_execute
|
||||
cursor.execute(statement, parameters)
|
||||
~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
|
||||
sqlite3.IntegrityError: CHECK constraint failed: quantity_positive
|
||||
|
||||
The above exception was the direct cause of the following exception:
|
||||
|
||||
Traceback (most recent call last):
|
||||
File "/tmp/babel-sg4Ps9/python-swDwMp", line 2, in <module>
|
||||
ship_it(2)
|
||||
~~~~~~~^^^
|
||||
File "<string>", line 14, in ship_it
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1421, in execute
|
||||
return meth(
|
||||
self,
|
||||
distilled_parameters,
|
||||
execution_options or NO_OPTIONS,
|
||||
)
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/sql/elements.py", line 526, in _execute_on_connection
|
||||
return connection._execute_clauseelement(
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
|
||||
self, distilled_params, execution_options
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
)
|
||||
^
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1643, in _execute_clauseelement
|
||||
ret = self._execute_context(
|
||||
dialect,
|
||||
...<8 lines>...
|
||||
cache_hit=cache_hit,
|
||||
)
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1848, in _execute_context
|
||||
return self._exec_single_context(
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~^
|
||||
dialect, context, statement, parameters
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
)
|
||||
^
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1988, in _exec_single_context
|
||||
self._handle_dbapi_exception(
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
|
||||
e, str_statement, effective_parameters, cursor, context
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
)
|
||||
^
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 2365, in _handle_dbapi_exception
|
||||
raise sqlalchemy_exception.with_traceback(exc_info[2]) from e
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/base.py", line 1969, in _exec_single_context
|
||||
self.dialect.do_execute(
|
||||
~~~~~~~~~~~~~~~~~~~~~~~^
|
||||
cursor, str_statement, effective_parameters, context
|
||||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
)
|
||||
^
|
||||
File "/home/octopus/study/Python/sqlalchemy-study/.venv/lib/python3.14/site-packages/sqlalchemy/engine/default.py", line 952, in do_execute
|
||||
cursor.execute(statement, parameters)
|
||||
~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
|
||||
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) CHECK constraint failed: quantity_positive
|
||||
[SQL: UPDATE cookies SET quantity=(cookies.quantity - ?) WHERE cookies.cookie_id = ?]
|
||||
[parameters: (4, 1)]
|
||||
(Background on this error at: https://sqlalche.me/e/20/gkpj)
|
||||
#+end_example
|
||||
|
||||
#+BEGIN_SRC python :results none :cache yes
|
||||
def ship_it(order_id: int) -> None:
|
||||
s = select(line_items.c.cookie_id, line_items.c.quantity)
|
||||
s = s.where(line_items.c.order_id == order_id)
|
||||
transaction = connection.begin()
|
||||
cookies_to_ship = connection.execute(s).fetchall()
|
||||
|
||||
try:
|
||||
for cookie in cookies_to_ship:
|
||||
u = update(cookies).where(cookies.c.cookie_id == cookie.cookie_id).values(quantity = cookies.c.quantity -cookie.quantity)
|
||||
result = connection.execute(u)
|
||||
u = update(orders).where(orders.c.order_id == order_id).values(shipped=True)
|
||||
result = connection.execute(u)
|
||||
print(f"Shipped order ID: {order_id}")
|
||||
transaction.commit()
|
||||
except IntegrityError as error:
|
||||
transaction.rollback()
|
||||
logging.exception()
|
||||
#+END_SRC
|
||||
** SQLAlchemy v2
|
||||
:PROPERTIES:
|
||||
:header-args: :cache yes
|
||||
:header-args:python: :tangle ch3-v2.py
|
||||
:header-args: :session *ch3-v2*
|
||||
:END:
|
||||
#+BEGIN_SRC python :results output :shebang "#!/usr/bin/env python3"
|
||||
#!/usr/bin/env python3
|
||||
import sys
|
||||
|
||||
sys.stderr = sys.stdout
|
||||
|
||||
import logging
|
||||
from datetime import datetime
|
||||
|
||||
from sqlalchemy import (
|
||||
Boolean,
|
||||
CheckConstraint,
|
||||
Column,
|
||||
DateTime,
|
||||
ForeignKey,
|
||||
Integer,
|
||||
MetaData,
|
||||
Numeric,
|
||||
PrimaryKeyConstraint,
|
||||
String,
|
||||
Table,
|
||||
UniqueConstraint,
|
||||
create_engine,
|
||||
insert,
|
||||
select,
|
||||
update,
|
||||
)
|
||||
from sqlalchemy.exc import IntegrityError
|
||||
from sqlparse import format as sqlformat
|
||||
|
||||
|
||||
def sqlf(
|
||||
sql: str | object,
|
||||
reindent=True,
|
||||
keyword_case="upper",
|
||||
indent_width=2,
|
||||
strip_comments=False,
|
||||
identifier_case="lower",
|
||||
):
|
||||
if not isinstance(sql, str):
|
||||
sql = str(sql)
|
||||
return sqlformat(
|
||||
sql,
|
||||
encoding="utf8",
|
||||
reindent=reindent,
|
||||
keyword_case=keyword_case,
|
||||
indent_width=indent_width,
|
||||
strip_comments=strip_comments,
|
||||
identifier_case=identifier_case,
|
||||
)
|
||||
|
||||
|
||||
metadata = MetaData()
|
||||
|
||||
cookies = Table(
|
||||
"cookies",
|
||||
metadata,
|
||||
Column("cookie_id", Integer(), primary_key=True),
|
||||
Column("cookie_name", String(50), index=True),
|
||||
Column("cookie_recipe_url", String(255), unique=True),
|
||||
Column("cookie_sku", String(55), unique=True),
|
||||
Column("quantity", Integer()),
|
||||
Column("unit_cost", Numeric(12, 2)),
|
||||
CheckConstraint("unit_cost >= 0.00", name="unit_cost_positive"),
|
||||
CheckConstraint("quantity >= 0", name="quantity_positive"),
|
||||
)
|
||||
|
||||
users = Table(
|
||||
"users",
|
||||
metadata,
|
||||
Column("user_id", Integer()),
|
||||
Column("username", String(15), nullable=False),
|
||||
Column("email_address", String(255), nullable=False),
|
||||
Column("phone", String(20), nullable=False),
|
||||
Column("password", String(25), nullable=False),
|
||||
Column("created_on", DateTime(), default=datetime.now),
|
||||
Column("updated_on", DateTime(), default=datetime.now, onupdate=datetime.now),
|
||||
PrimaryKeyConstraint("user_id", name="user_pk"),
|
||||
UniqueConstraint("username", name="uix_username"),
|
||||
)
|
||||
|
||||
orders = Table(
|
||||
"orders",
|
||||
metadata,
|
||||
Column("order_id", Integer(), primary_key=True),
|
||||
Column("user_id", ForeignKey("users.user_id")),
|
||||
Column("shipped", Boolean(), default=False),
|
||||
)
|
||||
|
||||
line_items = Table(
|
||||
"line_items",
|
||||
metadata,
|
||||
Column("line_items_id", Integer(), primary_key=True),
|
||||
Column("order_id", ForeignKey("orders.order_id")),
|
||||
Column("cookie_id", ForeignKey("cookies.cookie_id")),
|
||||
Column("quantity", Integer()),
|
||||
Column("extended_cost", Numeric(12, 2)),
|
||||
)
|
||||
|
||||
engine = create_engine("sqlite:///:memory:", echo=True)
|
||||
|
||||
with engine.begin() as connection:
|
||||
metadata.create_all(connection)
|
||||
|
||||
# --- insert одного пользователя ---
|
||||
ins = insert(users).values(
|
||||
username="cookiemon",
|
||||
email_address="mon@cookie.com",
|
||||
phone="111-111-1111",
|
||||
password="password",
|
||||
)
|
||||
connection.execute(ins)
|
||||
|
||||
# --- select возвращает Row, у которого есть .username ---
|
||||
s = select(users.c.username, users.c.password)
|
||||
results = connection.execute(s)
|
||||
try:
|
||||
[(row.username, row.password) for row in results]
|
||||
except AttributeError:
|
||||
logging.exception(results)
|
||||
|
||||
# --- проверка вставки ---
|
||||
s = select(users.c.username)
|
||||
print(connection.execute(s).fetchall())
|
||||
|
||||
# --- нарушение уникальности username ---
|
||||
ins = insert(users).values(
|
||||
username="cookiemon",
|
||||
email_address="damon@cookie.com",
|
||||
phone="111-111-1111",
|
||||
password="password",
|
||||
)
|
||||
try:
|
||||
with connection.begin_nested(): # SAVEPOINT, чтобы не убить внешнюю транзакцию
|
||||
connection.execute(ins)
|
||||
except IntegrityError:
|
||||
logging.exception(str(ins))
|
||||
|
||||
# --- массовая вставка cookies ---
|
||||
inventory_list = [
|
||||
{
|
||||
"cookie_name": "chocolate chip",
|
||||
"cookie_recipe_url": "http://some.aweso.me/cookie/recipe.html",
|
||||
"cookie_sku": "CC01",
|
||||
"quantity": "12",
|
||||
"unit_cost": "0.5",
|
||||
},
|
||||
{
|
||||
"cookie_name": "dark chocolate chip",
|
||||
"cookie_recipe_url": "http://some.aweso.me/cookie/recipe_dark.html",
|
||||
"cookie_sku": "CC02",
|
||||
"quantity": "1",
|
||||
"unit_cost": "0.75",
|
||||
},
|
||||
]
|
||||
connection.execute(insert(cookies), inventory_list)
|
||||
|
||||
# --- заказы ---
|
||||
connection.execute(insert(orders).values(user_id=1, order_id="1"))
|
||||
connection.execute(
|
||||
insert(line_items),
|
||||
[
|
||||
{
|
||||
"order_id": 1,
|
||||
"cookie_id": 1,
|
||||
"quantity": 9,
|
||||
"extended_cost": 4.50,
|
||||
}
|
||||
],
|
||||
)
|
||||
|
||||
connection.execute(insert(orders).values(user_id=1, order_id="2"))
|
||||
connection.execute(
|
||||
insert(line_items),
|
||||
[
|
||||
{
|
||||
"order_id": 2,
|
||||
"cookie_id": 1,
|
||||
"quantity": 4,
|
||||
"extended_cost": 1.50,
|
||||
},
|
||||
{
|
||||
"order_id": 2,
|
||||
"cookie_id": 2,
|
||||
"quantity": 1,
|
||||
"extended_cost": 4.50,
|
||||
},
|
||||
],
|
||||
)
|
||||
|
||||
|
||||
def ship_it(order_id: int) -> None:
|
||||
"""Версия без явной транзакции — каждый execute коммитится сам."""
|
||||
s = select(line_items.c.cookie_id, line_items.c.quantity).where(
|
||||
line_items.c.order_id == order_id
|
||||
)
|
||||
cookies_to_ship = connection.execute(s).fetchall()
|
||||
for cookie in cookies_to_ship:
|
||||
u = (
|
||||
update(cookies)
|
||||
.where(cookies.c.cookie_id == cookie.cookie_id)
|
||||
.values(quantity=cookies.c.quantity - cookie.quantity)
|
||||
)
|
||||
connection.execute(u)
|
||||
u = update(orders).where(orders.c.order_id == order_id).values(shipped=True)
|
||||
connection.execute(u)
|
||||
print(f"Shipped order ID: {order_id}")
|
||||
|
||||
|
||||
def ship_it_atomic(order_id: int) -> None:
|
||||
"""Версия с явной транзакцией и rollback при ошибке."""
|
||||
s = select(line_items.c.cookie_id, line_items.c.quantity).where(
|
||||
line_items.c.order_id == order_id
|
||||
)
|
||||
|
||||
with engine.begin() as conn:
|
||||
cookies_to_ship = conn.execute(s).fetchall()
|
||||
try:
|
||||
for cookie in cookies_to_ship:
|
||||
u = (
|
||||
update(cookies)
|
||||
.where(cookies.c.cookie_id == cookie.cookie_id)
|
||||
.values(quantity=cookies.c.quantity - cookie.quantity)
|
||||
)
|
||||
conn.execute(u)
|
||||
u = update(orders).where(orders.c.order_id == order_id).values(shipped=True)
|
||||
conn.execute(u)
|
||||
print(f"Shipped order ID: {order_id}")
|
||||
except IntegrityError:
|
||||
# with engine.begin() сам сделает rollback
|
||||
logging.exception("Failed to ship order %s", order_id)
|
||||
raise
|
||||
|
||||
|
||||
# --- используем транзакционную версию ---
|
||||
ship_it_atomic(1)
|
||||
s = select(cookies.c.cookie_name, cookies.c.quantity)
|
||||
with engine.connect() as conn:
|
||||
print(conn.execute(s).fetchall())
|
||||
|
||||
try:
|
||||
ship_it_atomic(2)
|
||||
except IntegrityError:
|
||||
logging.exception("")
|
||||
#+END_SRC
|
||||
|
||||
Reference in New Issue
Block a user