如何自动更新数据库到SQLAlchemy声明？

Question

sqlautocode - 在处理多对多关系时有问题

sqlsoup - 不支持关系

elixir - 它不会自动生成

还有其他我可以尝试的东西吗？

Answer 1

你可以使用 sqlacodegen 这个工具来从数据库中生成所有的模型。不过，你需要自己手动处理外键的部分。

Answer 2

理论上，在sqlalchemy中使用反射功能应该能满足你的需求。在这个例子中，我使用的是一个mssql数据库，里面有两个表，它们之间有简单的多对一关系：

一个叫“Tests”的表，包含以下字段：

id
testname
author_id（这是指向“Users”表的外键，关联到Users表的id字段）

另一个叫“Users”的表，包含以下字段：

id
fullname

所以下面的代码应该能反映出这个数据库的结构：

from sqlalchemy import *
from sqlalchemy.orm import create_session
from sqlalchemy.schema import Table, MetaData
from sqlalchemy.ext.declarative import declarative_base

#Create and engine and get the metadata
Base = declarative_base()
engine = create_engine('put your database connect string here')
metadata = MetaData(bind=engine)

#Reflect each database table we need to use, using metadata
class Tests(Base):
    __table__ = Table('Tests', metadata, autoload=True)

class Users(Base):
    __table__ = Table('Users', metadata, autoload=True)

#Create a session to use the tables    
session = create_session(bind=engine)

#Here I will just query some data using my foreign key relation,  as you would
#normally do if you had created a declarative data mode.
#Note that not all test records have an author so I need to accomodate for Null records
testlist = session.query(Tests).all()    

for test in testlist:
    testauthor = session.query(Users).filter_by(id=test.author_id).first()  
    if not testauthor:
        print "Test Name: {}, No author recorded".format(test.testname)
    else:
        print "Test Name: {}, Test Author: {}".format(test.testname, testauthor.fullname)

看起来这个方法能处理表之间的关系。不过，你还没有详细说明你具体想要做什么。

Answer 3

我试过这个方法，使用的是Northwind数据库，感觉还不错。不过，我需要添加一些关系字段，这样才能跟踪数据库之间的关系。

假设我在启动应用程序的时候对表之间的关系一无所知，我需要一种方法来自动生成这些关系。

import unittest

from sqlalchemy import *
from sqlalchemy.orm import create_session
from sqlalchemy.ext.declarative import declarative_base
from datetime import datetime
from sqlalchemy.orm import contains_eager, joinedload
from sqlalchemy.orm import relationship

#Create and engine and get the metadata
Base = declarative_base()
engine = create_engine('mssql://user:pass@Northwind', echo=True)
metadata = MetaData(bind=engine)


#Reflect each database table we need to use, using metadata
class Customer(Base):
    __table__ = Table('Customers', metadata, autoload=True)
    orders = relationship("Order", backref="customer")

class Shipper(Base):
    __table__ = Table('Shippers', metadata, autoload=True)
    orders = relationship("Order", backref="shipper")

class Employee(Base):
    __table__ = Table('Employees', metadata, autoload=True)
#    orders = relationship("Order", backref="employee")
    territories = relationship('Territory', secondary=Table('Employeeterritories', metadata, autoload=True))

class Territory(Base):
    __table__ = Table('Territories', metadata, autoload=True)
    region = relationship('Region', backref='territories')

class Region(Base):
    __table__ = Table('Region', metadata, autoload=True)


class Order(Base):
    __table__ = Table('Orders', metadata, autoload=True)
    products = relationship('Product', secondary=Table('Order Details', metadata, autoload=True))
    employee = relationship('Employee', backref='orders')

class Product(Base):
    __table__ = Table('Products', metadata, autoload=True)
    supplier = relationship('Supplier', backref='products')
    category = relationship('Category', backref='products') 

class Supplier(Base):
    __table__ = Table('Suppliers', metadata, autoload=True)

class Category(Base):
    __table__ = Table('Categories', metadata, autoload=True)


class Test(unittest.TestCase):

    def setUp(self):
        #Create a session to use the tables    
        self.session = create_session(bind=engine)        

    def tearDown(self):
        self.session.close()

    def test_withJoins(self):
        q = self.session.query(Customer)
        q = q.join(Order)
        q = q.join(Shipper)
        q = q.filter(Customer.CustomerID =='ALFKI')
        q = q.filter(Order.OrderID=='10643')
        q = q.filter(Shipper.ShipperID=='1')
        q = q.options(contains_eager(Customer.orders, Order.shipper))
        res = q.all()
        cus = res[0]
        ord = cus.orders[0]
        shi = ord.shipper
        self.assertEqual(shi.Phone, '(503) 555-9831')

如何自动更新数据库到SQLAlchemy声明？

3 个回答

撰写回答