如何在Flask-SQLAlchemy应用程序中执行原始SQL

Question

如何在SQLAlchemy中执行原始SQL？我有一个python web应用程序，它运行在烧瓶上，并通过SQLAlchemy与数据库连接。我需要一种方法来运行原始SQL。该查询涉及多个表连接以及内联视图。我试过了：connection = db.session.connection()connection.execute( <sql here> )但我不断收到网关错误。

Answer 1

你有没有尝试过：

result = db.engine.execute("<sql here>")

要么：

from sqlalchemy import text

sql = text('select name from penguins')

result = db.engine.execute(sql)

names = [row[0] for row in result]

print names

Answer 2

SQL Alchemy会话对象有自己的execute方法：

result = db.session.execute('SELECT * FROM my_table WHERE my_column = :val', {'val': 5})

您的所有查询都应该通过会话对象，无论它们是否是原始SQL。这可确保查询由事务正确管理，从而允许将同一请求中的多个查询作为单个单元提交或回滚。使用引擎或连接走出事务会使您面临更大的微妙风险，可能很难检测到可能导致数据损坏的错误。每个请求应仅与一个事务相关联，并且使用db.session将确保您的应用程序的情况。

假设它是一个SELECT查询，这将返回一个可迭代的RowProxy对象。

您可以使用各种技术访问各个列：

for r in result:

    print(r[0]) # Access by positional index

    print(r['my_column']) # Access by column name as a string

    r_dict = dict(r.items()) # convert to dict keyed by column names

就个人而言，我更喜欢将结果转换为namedtuples：

from collections import namedtuple

Record = namedtuple('Record', result.keys())

records = [Record(*r) for r in result.fetchall()]

for r in records:

    print(r)

如果您没有使用Flask-SQLAlchemy扩展，您仍然可以轻松使用会话：

import sqlalchemy

from sqlalchemy.orm import sessionmaker, scoped_session

engine = sqlalchemy.create_engine('my connection string')

Session = scoped_session(sessionmaker(bind=engine))

s = Session()

result = s.execute('SELECT * FROM my_table WHERE my_column = :val', {'val': 5})

Answer 3

docs：SQL表达式语言教程 - 使用文本

例：

from sqlalchemy.sql import text

connection = engine.connect()

# recommended

cmd = 'select * from Employees where EmployeeGroup == :group'

employeeGroup = 'Staff'

employees = connection.execute(text(cmd), group = employeeGroup)

# or - wee more difficult to interpret the command

employeeGroup = 'Staff'

employees = connection.execute(

                  text('select * from Employees where EmployeeGroup == :group'), 

                  group = employeeGroup)

# or - notice the requirement to quote "Staff"

employees = connection.execute(

                  text('select * from Employees where EmployeeGroup == "Staff"'))

for employee in employees: logger.debug(employee)

# output

(0, u'Tim', u'Gurra', u'Staff', u'991-509-9284')

(1, u'Jim', u'Carey', u'Staff', u'832-252-1910')

(2, u'Lee', u'Asher', u'Staff', u'897-747-1564')

(3, u'Ben', u'Hayes', u'Staff', u'584-255-2631')