title: Query Django model based on relationship between ForeignKey sub elements
body: <pre><code>class Price(models.Model):
      date = models.DateField()
      price = models.DecimalField(max_digits=6, decimal_places=2)
      product = models.ForeignKey("Product")
  
  class Product(models.Model):
      name = models.CharField(max_length=256)
      price_history = models.ManyToManyField(Price, related_name="product_price", blank=True)
  </code></pre>
  
  <p>I want to query Product such that I return only those products for whom the price on date x is higher than any earlier date.</p>
  
  <p>Thanks boffins.</p>