django db query, getting error

here is my model :

 class company_profile(models.Model):
       user=models.ForeignKey(User, unique=True)
       company=models.CharField(max_length=200)

      def __unicode__(self):
            return self.company

and when i got django shell i did the following, it worked correctly :

  from my_app.models import company_profile
  everything = company_profile.objects.all()
  # this gives me the correct out put of the existing company names , 

but when i do the following :

  username = company_profile.objects.all().filer(user='rakesh')

  this is the error , that i am getting : 

  ValueError: invalid literal for int() with base 10: 'rakesh'

how can i solve this , or is my query wrong.