old_contents: from django.db import models
  from datetime import datetime
  from django.utils import timezone
  from django.conf import settings
  from django.core.urlresolvers import reverse
  # Create your models here.
  
  class Author(models.Model):
  	first_name = models.CharField(max_length=60)
  	last_name = models.CharField(max_length=60)
  	email = models.EmailField(blank=True)
  	def __str__(self):
  		return self.first_name + ' ' + self.last_name
  
  class Publisher(models.Model):
  	"""docstring for Publisher"""
  	name = models.CharField(max_length=200)
  	address = models.TextField(blank=True)
  	website = models.URLField(blank=True)
  	def __str__(self):
  		return self.name		
  
  class Book(models.Model):
  	name = models.CharField(max_length=200)
  	edition = models.SmallIntegerField(default=1)
  	authors = models.ManyToManyField(Author, blank=True)
  	publisher = models.ManyToManyField(Publisher, blank=True)
  	published = models.PositiveSmallIntegerField(blank=True)
  	pages = models.IntegerField(default=0)
  	isbn_10	= models.IntegerField(default=0,help_text="Do not include dashes")
  	isbn_13	= models.IntegerField(default=0,help_text="Do not include dashes")
  	description = models.TextField()
  	cover_image	= models.ImageField('cover Image',
                                  upload_to='cover_pics/%Y-%m-%d/',
                                  null=True,
                                  blank=True)
  	date_added = models.DateTimeField(default=datetime.now)
  	available = models.BooleanField(default=True)
  	# this method causes a button labelled "View on site" to 
  	# appear in the top right-hand side in book admin page.
  	def get_absolute_url(self):
  		return reverse('books:book_detail', args=[self.id])
  
  	def __str__(self):
  		if self.edition==1:
  			nth="st"
  		elif self.edition==2:
  			nth="nd"
  		elif self.edition==3:
  			nth="rd"
  		else : nth="th"
  		return self.name + ", "+ str(self.edition)+nth + " Edition"
  
  	def was_added_recently(self):
  		return self.date_added >= timezone.now() - datetime.timedelta(days=30)
  
  class Loaned(models.Model):
  	loaned_by = models.ForeignKey(settings.AUTH_USER_MODEL)
  	book = models.ForeignKey(Book)
  
  	class Meta:
  		verbose_name = "Loaned Book"
new_contents: from django.db import models
  from datetime import datetime
  from django.utils import timezone
  from django.conf import settings
  from django.core.urlresolvers import reverse
  # Create your models here.
  
  class Author(models.Model):
  	first_name = models.CharField(max_length=60)
  	last_name = models.CharField(max_length=60)
  	email = models.EmailField(blank=True)
  	def __str__(self):
  		return self.first_name + ' ' + self.last_name
  
  class Publisher(models.Model):
  	"""docstring for Publisher"""
  	name = models.CharField(max_length=200)
  	address = models.TextField(blank=True)
  	website = models.URLField(blank=True)
  	def __str__(self):
  		return self.name		
  
  class Book(models.Model):
  	name = models.CharField(max_length=200)
  	edition = models.SmallIntegerField(default=1)
  	authors = models.ManyToManyField(Author, blank=True)
  	publisher = models.ManyToManyField(Publisher, blank=True)
  	published = models.PositiveSmallIntegerField(blank=True)
  	pages = models.IntegerField(default=0)
  	isbn_10	= models.IntegerField(default=0,help_text="Do not include dashes")
  	isbn_13	= models.IntegerField(default=0,help_text="Do not include dashes")
  	description = models.TextField()
  	cover_image	= models.ImageField('cover Image',
                                  upload_to='cover_pics/%Y-%m-%d/',
                                  null=True,
                                  blank=True)
  	date_added = models.DateTimeField(default=datetime.now)
  	available = models.BooleanField(default=True)
  	# this method causes a button labelled "View on site" to 
  	# appear in the top right-hand side in book admin page.
  	def get_absolute_url(self):
  		return reverse('books:book_detail', args=[self.id])
  
  	def __str__(self):
  		if self.edition==1:
  			nth="st"
  		elif self.edition==2:
  			nth="nd"
  		elif self.edition==3:
  			nth="rd"
  		else : nth="th"
  		return self.name + ", "+ str(self.edition)+nth + " Edition"
  
  	def was_added_recently(self):
  		return self.date_added >= timezone.now() - datetime.timedelta(days=30)
  
  
  class Loaned(models.Model):
  	loaned_by = models.ForeignKey(settings.AUTH_USER_MODEL)
  	book = models.ForeignKey(Book)
  	timestamp = models.DateTimeField()
  	
  	class Meta:
  		verbose_name = "Loaned Book"
subject: Add time stamp field to model