sqlalchemy使用總結(一)-執行原始sql語句

時間  2019-11-22
標籤 sqlalchemy 使用 總結 執行 原始 sql 語句 欄目 SQL 简体版
原文   原文鏈接

參考文檔

官方文檔首頁html

鏈接數據庫

這邊使用sqlite的內存數據庫，方便測試python

import sqlalchemy

db_engine = sqlalchemy.create_engine('sqlite:///:memory:', echo=True)
db_conn = db_engine.connect()

使用create_engine能夠創建一個鏈接池，調用connect能夠從鏈接池中獲取一個鏈接,調用db_conn.close()會把鏈接釋放給鏈接池,並作相應的清理工做。sql

官方說明數據庫

The connection is an instance of Connection, which is a proxy object for an actual DBAPI connection. The DBAPI connection is retrieved from the connection pool at the point at which Connection is created.ide

The returned result is an instance of ResultProxy, which references a DBAPI cursor and provides a largely compatible interface with that of the DBAPI cursor. The DBAPI cursor will be closed by the ResultProxy when all of its result rows (if any) are exhausted. A ResultProxy that returns no rows, such as that of an UPDATE statement (without any returned rows), releases cursor resources immediately upon construction.測試

When the close() method is called, the referenced DBAPI connection is released to the connection pool. From the perspective of the database itself, nothing is actually 「closed」, assuming pooling is in use. The pooling mechanism issues a rollback() call on the DBAPI connection so that any transactional state or locks are removed, and the connection is ready for its next usage.fetch

使用原始SQL

先進行建表操做日誌

db_conn.execute(r'''
CREATE TABLE IF NOT EXISTS stocks (
        date text, 
        trans text, 
        symbol text, 
        qty real, 
        pricereal
    )
''')

插入單條數據

直接拼裝一個完整的sql字符串，或使用下面防注入的參數綁定方式, 注意:會自動commitcode

db_conn.execute(r'''
INSERT INTO stocks VALUES (?, ?, ?, ?, ?)
''', ('2001-01-11', 'BUY', 'RHAT', 100, 35.14) )
db_conn.execute(r'''
INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
''', ('2001-01-11', 'BUY', 'RHAT', 100, 35.14) )

操做日誌顯示會自動commitsqlite

2017-08-27 15:05:26,834 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:05:26,834 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:05:26,834 INFO sqlalchemy.engine.base.Engine 
INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)

2017-08-27 15:05:26,834 INFO sqlalchemy.engine.base.Engine ('2001-01-11', 'BUY', 'RHAT', 100, 35.14)
2017-08-27 15:05:26,834 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine 
INSERT INTO stocks VALUES (?, ?, ?, ?, ?)

2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine ('2001-01-11', 'BUY', 'RHAT', 100, 35.14)
2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine 
INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)

插入多條數據

與插入單條數據相似, 注意:會自動commit

purchases = [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
             ('2006-04-05', 'BUY', 'MSFT', 1000, 72.00),
             ('2006-04-06', 'SELL', 'IBM', 500, 53.00),
            ]
db_conn.execute(r'''
INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
''', purchases)
db_conn.execute(r'''
INSERT INTO stocks VALUES (?, ?, ?, ?, ?)
''', purchases)

操做日誌顯示會自動commit

2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine 
INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)

2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine [('2006-03-28', 'BUY', 'IBM', 1000, 45.0), ('2006-04-05', 'BUY', 'MSFT', 1000, 72.0), ('2006-04-06', 'SELL', 'IBM', 500, 53.0)]
2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine 
INSERT INTO stocks VALUES (?, ?, ?, ?, ?)

2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine [('2006-03-28', 'BUY', 'IBM', 1000, 45.0), ('2006-04-05', 'BUY', 'MSFT', 1000, 72.0), ('2006-04-06', 'SELL', 'IBM', 500, 53.0)]
2017-08-27 15:05:26,835 INFO sqlalchemy.engine.base.Engine COMMIT

使用事務處理

參考文檔

因爲上面的插入操做會自動進行commit，sqlalchemy提供了Transactions來管理commit和rollback。

完整的測試代碼以下

import sqlalchemy

db_engine = sqlalchemy.create_engine('sqlite:///:memory:', echo=True, pool_size=2)
db_conn = db_engine.connect()

db_conn.execute(r'''
CREATE TABLE IF NOT EXISTS stocks (date text, trans text, symbol text, qty real, price real)
''')

with db_conn.begin() as db_trans:
    #
    db_conn.execute(r'''
    INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
    ''', ('aa', 'BUY', 'RHAT', 100, 35.14) )

    db_conn.execute(r'''
    INSERT INTO stocks VALUES (?, ?, ?, ?, ?)
    ''', ('bb', 'BUY', 'RHAT', 100, 35.14) )

    #提早進行commit
    db_trans.commit()

    purchases = [('cc', 'BUY', 'IBM', 1000, 45.00),
                 ('dd', 'BUY', 'MSFT', 1000, 72.00),
                 ('ee', 'SELL', 'IBM', 500, 53.00),
                ]
    db_conn.execute(r'''
    INSERT INTO stocks VALUES (?,?,?,?,?)
    ''', purchases)


query_result = db_conn.execute(r'''
SELECT * FROM  stocks
''').fetchall()
print('query_result:', query_result)

完整的日誌以下

2017-08-27 15:18:22,057 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1
2017-08-27 15:18:22,057 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:18:22,057 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1
2017-08-27 15:18:22,057 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine 
CREATE TABLE IF NOT EXISTS stocks (date text, trans text, symbol text, qty real, price real)

2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine 
    INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
    
2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine ('aa', 'BUY', 'RHAT', 100, 35.14)
2017-08-27 15:18:22,058 INFO sqlalchemy.engine.base.Engine 
    INSERT INTO stocks VALUES (?, ?, ?, ?, ?)
    
2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine ('bb', 'BUY', 'RHAT', 100, 35.14)
2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine 
    INSERT INTO stocks VALUES (?,?,?,?,?)
    
2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine [('cc', 'BUY', 'IBM', 1000, 45.0), ('dd', 'BUY', 'MSFT', 1000, 72.0), ('ee', 'SELL', 'IBM', 500, 53.0)]
2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine 
SELECT * FROM  stocks

2017-08-27 15:18:22,059 INFO sqlalchemy.engine.base.Engine ()
query_result: [('aa', 'BUY', 'RHAT', 100.0, 35.14), ('bb', 'BUY', 'RHAT', 100.0, 35.14), ('cc', 'BUY', 'IBM', 1000.0, 45.0), ('dd', 'BUY', 'MSFT', 1000.0, 72.0), ('ee', 'SELL', 'IBM', 500.0, 53.0)]

能夠看到有三次commit操做,有三次commit操做， 一次是建表， 兩次是插入，其中第二次是顯示調用commit,第三次是with結束後自動調用。所以若是想避免頻繁的commit，能夠使用with來進行上下文管理。

測試異常

import sqlalchemy

db_engine = sqlalchemy.create_engine('sqlite:///:memory:', echo=True, pool_size=2)
db_conn = db_engine.connect()

try:
    with db_conn.begin() as db_trans:
        db_conn.execute(r'''
        CREATE TABLE IF NOT EXISTS stocks (date text, trans text, symbol text, qty real, price real)
        ''')

        db_conn.execute(r'''
        INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
        ''', ('aa', 'BUY', 'RHAT', 100, 35.14) )
        db_trans.commit()

        db_conn.execute(r'''
        INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
        ''', ('bb', 'BUY', 'RHAT', 100, 35.14) )

        db_conn.execute(r'''
        INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
        ''', ('cc', 'BUY', 'RHAT', 100) ) #這裏故意少傳一個參數來製造異常
except:
    print('exception!!!')


query_result = db_conn.execute(r'''
SELECT * FROM  stocks
''').fetchall()
print('query_result:', query_result)

日誌

2017-08-27 15:40:53,151 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1
2017-08-27 15:40:53,151 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:40:53,152 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1
2017-08-27 15:40:53,152 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:40:53,152 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2017-08-27 15:40:53,152 INFO sqlalchemy.engine.base.Engine 
        CREATE TABLE IF NOT EXISTS stocks (date text, trans text, symbol text, qty real, price real)
        
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine ()
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine 
        INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
        
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine ('aa', 'BUY', 'RHAT', 100, 35.14)
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine 
        INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
        
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine ('bb', 'BUY', 'RHAT', 100, 35.14)
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine COMMIT
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine 
        INSERT INTO stocks VALUES (:1, :2, :3, :4, :5)
        
2017-08-27 15:40:53,153 INFO sqlalchemy.engine.base.Engine ('cc', 'BUY', 'RHAT', 100)
2017-08-27 15:40:53,154 INFO sqlalchemy.engine.base.Engine ROLLBACK
exception!!!
2017-08-27 15:40:53,154 INFO sqlalchemy.engine.base.Engine 
SELECT * FROM  stocks

2017-08-27 15:40:53,154 INFO sqlalchemy.engine.base.Engine ()
query_result: [('aa', 'BUY', 'RHAT', 100.0, 35.14), ('bb', 'BUY', 'RHAT', 100.0, 35.14)]
  • 出現異常時會自動rollback
  • 若是在with中提早調用commit，會致使之後的每一個改動操做都會自動commit
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