title: Better way to represent Many to many relationship in django admin
body: <p>I have a unique problem the way it should be handled in django admin.</p>
  
  <p>I have following models structure...</p>
  
  <pre><code>class Product(models.Model):
      name    = models.CharField(max_length = 100)
      base_price = models.DecimalField(max_digits = 5, decimal_places = 2)
  
  
      def __unicode__(self):
          return self.name
  
  
  class Country(models.Model):
      name = models.CharField(max_length = 2)
      base_price = models.DecimalField(max_digits = 5, decimal_places = 2)    
  
      def __unicode__(self):
          return self.name
  
  
  class CountryProduct(models.Model):
      country = models.ForeignKey(Country)
      product = models.ForeignKey(Product)
      overriden_price = models.DecimalField(max_digits = 5, decimal_places = 2)
  
      class Meta:
          unique_together = (("country", "product"),)
  </code></pre>
  
  <p>As shown here there is many to many relationship between products and countries.... I want to provide admin interface for overriding base price for given country and product. </p>
  
  <p>One option to have ui as follows, here dash (-) represents default price and value in number represents override price for given country and product.</p>
  
  <pre><code>countries -&gt; | US  | UK 
  products     |     |
  ---------------------------
  Product1     |  -  |  10
  Product2     |  5  |   7
  </code></pre>
  
  <p>But I don't know how to do that.... </p>
  
  <p>I am open to look at alternative approaches (including changes in model structure) as well as long as it meets the requirement... Your input of any sort will definitely be useful to me...</p>
  
  <p>Thanks in Advance :)</p>