select_from（table_name）中的table_name是什么类型？

Question

I'm trying to get the number of rows from a SQL Server which consists of many tables by looping through it to see how much data they contain. However, I'm not sure what will go into select_from() function. As I currently supply Unicode for table names and it raised

NoInspectionAvailable: No inspection system is available for object of type <type 'unicode'>

The code that I used was

from sqlalchemy import create_engine
import urllib
from sqlalchemy import inspect
import sqlalchemy
from sqlalchemy import select, func, Integer, Table, Column, MetaData
from sqlalchemy.orm import sessionmaker

connection_string = "DRIVER={SQL Server}; *hidden*"
connection_string = urllib.quote_plus(connection_string) 
connection_string = "mssql+pyodbc:///?odbc_connect=%s" % connection_string

engine = sqlalchemy.create_engine(connection_string)
Session = sessionmaker()
Session.configure(bind=engine) 
session = Session()
connection = engine.connect()
inspector = inspect(engine)

for table_name in inspector.get_table_names():
           print session.query(func.count('*')).select_from(table_name).scalar()

Answer 1

Typically, it's a class name that refers to a class that describes the database table.

In the sqlalchemy docs, http://docs.sqlalchemy.org/en/latest/orm/tutorial.html , they have you create a base class using declarative base and then create child classes for each table you want to query. You would then pass that class name into the select_from function unquoted.

The Flask framework provides a built-in base class that is ready for use called db.Model and Django has one called models.Model.

Alternatively, you can also pass queries. I use the Flask framework typically for python so I usually initiate queries like this:

my_qry = db.session.query(Cust).filter(Cust, Cust.cust == 'lolz')
results = my_qry.all()

On a side note, if you decide to look at .NET they also have nice ORMs. Personally, I favor Entity Framework, but Linq to SQL is out there, too.