class Company(models.Model)
    name = models.CharField(max_length=200)
    client_id = models.ForeignKey(User)

class Bill(models.Model)
    deal_num = models.CharField(max_length=200)
    company = models.ForeignKey(Company)

I do the
>>> Company.objects.filter(client=request.user)
Company 1
---bill 101
---bill 102
---bill 103
Company 2
---bill 5401
---bill 402
---bill 803

Now i wont add search by bill number
And i do the
>>> Company.objects.filter(client=request.user, bill__bill_num__startswith=540)
Result:
Company 2
---bill 5401
---bill 402
---bill 803

But I like it
Company 2
---bill 5401