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from django.db import models
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class Author(models.Model):
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name = models.CharField(max_length=100)
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age = models.IntegerField()
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friends = models.ManyToManyField('self', blank=True)
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class Publisher(models.Model):
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name = models.CharField(max_length=255)
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num_awards = models.IntegerField()
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class Book(models.Model):
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isbn = models.CharField(max_length=9)
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name = models.CharField(max_length=255)