title: django.core.exceptions.FieldError: Unknown field(s) in ModelForm
body: <p>After adding a ModelForm and specifying the fields, I get this error when I try to makemigrations.  New to django and programming in general, so probably something dumb.</p>
  <p>django.core.exceptions.FieldError: Unknown field(s) (handling_time, holding_time, encounter_date, crate_time) specified for Encounter</p>
  <p>Models.py:</p>
  <pre><code>from django.db import models
  from django.conf import settings
  import datetime 
  
  class Animal(models.Model):
      Name = models.CharField(max_length=64, unique=True)
      Inactive_Date = models.DateField(null=True, default=None, blank=True)
      ANIMAL_TYPE_CHOICES = [
          ('Alligator', 'Alligator'),
          ('Alpaca', 'Alpaca'),
          ('Anteater', 'Anteater'),
          ('Armadillo', 'Armadillo'),
          ('Cat', 'Cat'),
          ('Chicken', 'Chicken'),
          ('Chinchilla', 'Chinchilla'),
          ('Donkey', 'Donkey'),
          ('Frog', 'Frog'),
          ('Goat', 'Goat'),
          ('Horse', 'Horse'),
          ('Insect', 'Insect'),
          ('Lizard', 'Lizard'),
          ('Millipede', 'Millipede'),
          ('Owl', 'Owl'),
          ('Penguin', 'Penguin'),
          ('Pig', 'Pig'),
          ('Snake', 'Snake'),
          ('Spider', 'Spider'),
          ('Tenrec', 'Tenrec'),
          ('Turtle', 'Turtle'),
      ]
      Animal_Type = models.CharField(
          max_length=32,
          choices=ANIMAL_TYPE_CHOICES,
          default='Cassowary')
      Comments = models.CharField(max_length=255)
      def __str__(self) -&gt; str:
          return ('Animal: ' + self.Name)
      def delete(self):
          self.Inactive_Date = datetime.datetime.today()
          self.save()
  
  class Encounter(models.Model):
      encounter_date = models.DateField
      animal = models.ForeignKey(Animal,null = True, on_delete=models.SET_NULL)
      user = models.ForeignKey(settings.AUTH_USER_MODEL,null = True, on_delete=models.SET_NULL)
      handling_time = models.BigIntegerField
      crate_time = models.BigIntegerField
      holding_time = models.BigIntegerField
      comments = models.CharField(max_length=255)
      def __str__(self) -&gt; str:
          return ('Encounter: ' + self.User.username + '/' + self.Animal.Name)
  </code></pre>
  <p>Forms.py:</p>
  <pre><code>from django.forms import ModelForm
  from encounters.models import Animal, Encounter
  import datetime
  
  class Open_Encounter_Form(ModelForm):
      class Meta:
          model = Encounter
          fields = ['encounter_date', 'user','animal','handling_time','crate_time','holding_time','comments']
  </code></pre>
  <p>Views.py:</p>
  <pre><code>from encounters.models import Animal, Encounter
  from django.shortcuts import render
  from django.contrib.auth import get_user_model
  from django.views import generic
  from django import forms
  from django.http import HttpResponseRedirect
  from .forms import Open_Encounter_Form
  
  # Create your views here.
  
  def index(request):
  
      num_animals = Animal.objects.all().count()
      User = get_user_model()
      num_users = User.objects.all().count()
      num_encounters = Encounter.objects.all().count()
  
      context = {
          'num_animals': num_animals,
          'num_users': num_users,
          'num_encounters': num_encounters,
      }
  
      return render(request, 'index.html', context = context)
  
  def open_encounter(request):
      if request.method == 'POST':
          form = Open_Encounter_Form(request.POST)
          if form.is_valid():
              #save the data
              aRecord=form.save()
              return HttpResponseRedirect('/Encounter saved')
      else:
          form=Open_Encounter_Form()
      return render(request, 'open_encounter.html', {'form', form})
  </code></pre>