How to automatically reflect database to sqlalchemy declarative?

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.