Building Scalable Web Applications/Building a Blog

from google.appengine.ext import db

class BlogIndex(db.Model):
 max_index = db.IntegerProperty(required=True,default=0)

class BlogEntry(db.Model):
 index = db.IntegerProperty(required=True)
 title = db.StringProperty(required=True)
 body  = db.TextProperty(required=True)


def post_entry(blogname, title, body):
 def txn():
   blog_index = BlogIndex.get_by_key_name(blogname)
   if blog_index is None:
     blog_index = BlogIndex(key_name=blogname)
   new_index = blog_index.max_index
   blog_index.max_index += 1
   blog_index.put()
   new_entry = BlogEntry(key_name=blogname + str(new_index),parent=blog_index, index=new_index,title=title, body=body)
   new_entry.put()
 db.run_in_transaction(txn)

def get_entry(blogname, index):
 entry = BlogEntry.get_by_key_name(blogname + str(index),parent=Key.from_path('BlogIndex',blogname))
 return entry


def get_entries(start_index):
 extra = None
 if start_index is None:
   entries = BlogEntry.gql(
       'ORDER BY index DESC').fetch(POSTS_PER_PAGE + 1)
 else:
   start_index = int(start_index)
   entries = BlogEntry.gql(
       'WHERE index <= :1 ORDER BY index DESC',         start_index).fetch(POSTS_PER_PAGE + 1)   if len(entries) > POSTS_PER_PAGE:
   extra = entries[-1]
   entries = entries[:POSTS_PER_PAGE]
 return entries, extra