title: Django getter on model field
body: <p>I'm using <strong>Django 2.x</strong></p>
  
  <p>I have a model like</p>
  
  <pre><code>class MyModel(models.Model):
      name = models.CharField()
      balance = models.IntegerField()
  </code></pre>
  
  <p>I want to change the value of balance on the GET request without changing the value in the database.</p>
  
  <p>Like if it could be <strong>@Property</strong> field, the model will look like</p>
  
  <pre><code>class MyModel(models.Model):
      name = models.CharField()
      balance = models.IntegerField()
  
      @property
      def balance(self):
          if balance:
             return balance
          return 0.15 * 50
  </code></pre>
  
  <p>But redeclaration is not allowed. How can I solve this issue?</p>
  
  <p>Note: Field should be compatible with <strong>ModelAdmin</strong> and <strong>DRF Serializer</strong></p>