title: Django database fields for better queries
body: <p>Hello I would like to ask a question for setting up some fields in my db. I have three models</p>
  
  <p>models</p>
  
  <pre><code>class Customer(models.Model):
      #fields
  
  
  class Entry(models.Model):
      #fields
      customer = models.ForeignKey(Customer, related_name='entries')
  
  
  class EntryHistory(models.Model):
      #fields
      entry = models.OneToOne(Entry, related_name='history')
  </code></pre>
  
  <p>I want to get all Entry histories for a specific customer. Isn't that</p>
  
  <pre><code>for entry in customer.entries:
      try:
          history.append(entry.history)
      except entry.history.related.models.DoesNotExist:
          pass(or continue?)
  </code></pre>
  
  <p>My thought search all customers entries and if they have a history added to the list. Would it be better if i just added a customer field in the EntryHistory?Would the query be quicker? This would be a frequent transaction in my project. But i know adding a customer in the EntryHistory model is redundant since I know who the customer is from the entry field. Should I be worried if e.g i have a lot of customers and a lot of entries for each?</p>