How to automatically reflect database to sqlalchemy declarative?

问题

sqlautocode - has issues with many-to-many relations

sqlsoup - doesn't support relations

elixir - it's note auto-generate

Is there something else I could try?

回答1:

In theory reflection in sqlalchemy should work for you. In this case I'm using an mssql database with two tables which have a simple Many-to-one relation:

"Tests" with fields:

id
testname
author_id (foreign key to the Users table, Users.id field)

"Users" with fields:

id
fullname

So the following should reflect the database:

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)

So this appears to work with table relations. Although you still haven't given much detail to exactly what you are trying to do.

回答2:

Well I went through that, tried on Northwind database and it looks promising. Although, I had to add relationship field to be able to follow database relations.

Let's consider that I don't know relations between tables at the moment of starting the application so I need is a way to generate automatically.

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')

回答3:

You could use sqlacodegen to generate all the models from the database. However you need to take care of the foreign key manually.

来源：https://stackoverflow.com/questions/6290162/how-to-automatically-reflect-database-to-sqlalchemy-declarative

标签

python

sqlalchemy

declarative

auto-generate