title: django foreign key Cannot assign must be a instance
body: <p>I am developing a web app using Django. I have created the table in MySQL database and then generated the models.py using inspectdb. I am able to fetch details and connect to the database without any issues. But while saving the values to the particular table, below error is shown </p>
  
  <pre><code>sav_list = List(id=4, item_name ='name1', item_desc='desc1', location='location', reason='rfp',  pid=3)
  </code></pre>
  
  <p>Cannot assign "3": "List.id" must be a "Order" instance.</p>
  
  <p>my models</p>
  
  <pre><code>class List(models.Model):
      id = models.IntegerField(db_column='ID', primary_key=True)  # Field name made lowercase.
      item_name = models.CharField(db_column='Item_Name', max_length=255)  # Field name made lowercase.
      item_desc = models.CharField(db_column='Item_Desc', max_length=300)  # Field name made lowercase.
      location = models.CharField(db_column='Location', max_length=100, blank=True, null=True)  # Field name made lowercase.
      reason = models.CharField(db_column='Reason', max_length=100, blank=True, null=True)  # Field name made lowercase.
      pid = models.ForeignKey('Order', models.DO_NOTHING, db_column='PID')  # Field name made lowercase.
  
  class Order(models.Model):
      poid = models.IntegerField(db_column='POID', primary_key=True)  # Field name made lowercase.
      po = models.CharField(db_column='PO', unique=True, max_length=20)  # Field name made lowercase.
      quote = models.CharField(db_column='Quote', unique=True, max_length=20)  # Field name made lowercase.
      condition = models.CharField(db_column='Condition', max_length=15)  # Field name made lowercase.
  </code></pre>
  
  <p>I have tried relate_name for foreign key but still same behaviour. Same values can be stored on database without any issues. Only Django throws an error. </p>
  
  <p>Please someone help me!!!</p>