Django-ORM: Illustrate a precise query for the situation - django

Question

I have 4 models in my project. Which are :
class Company(Group):
address_1 = models.CharField(max_length = 300, blank = True, null = True)
web_site = models.URLField(blank = True, null = True)
office_number = models.CharField(max_length = 20, blank = True, null = True)
class Person(models.Model):
user = models.ForeignKey(User)
company = models.ForeignKey(Company)
class Project(models.Model):
name = models.CharField(max_length = 100)
person = models.ManyToManyField(User, through = 'UserProject')
class UserProject(models.Model):
user = models.ForeignKey(User)
project = models.ForeignKey(Project)
is_owner = models.BooleanField(default = False)
In a view I would want to get
All the projects related to the request.user
The companies that are working on those projects
and the employees of those companies
I have tried writing some code but the queries are not precise. Help would be appreciated!

Answer 1

All projects related to request.user is easy, of course:
Project.objects.filter(person=request.user)
The companies working on those projects necessarily requires you to loop through the projects:
for p in projects:
p.company_set.all()
You have no relationship between User and Company, or any other foreign key on Company for that matter, so I have no idea where the concept of "employee" comes from or how to get that.
Since, this is pretty basic stuff, I'm assuming your issue is with the fact 1*N queries that are generated. In the current version of Django (1.3.1), there's no way to optimize this futher. In Django 1.4, there's prefetch_related that will allow you to select all the companies (and employees) with the Projects. However, it still requires a unique query for each relationship, so 3 total to get projects, companies, and employees. It works like this:
Project.objects.filter(person=request.user).prefetch_related('company')
In the mean time, I've had some success with using django-batch-select, which basically tries to emulate the behavior of prefetch_related.

Answer 2

OK some bugs in your models:
Project has a M2M on User through UserProject, which is fine, except I think you mean for it to have a M2M on Person which has a FK to User
Secondly, you haven't set up any relations to Company. there is no way to do item 2 on your list until that bug is fixed.
Why is Company extending Group? I must be missing something.
There is no Employee model
Example:
class Company(models.Model):
address_1 = models.CharField(max_length = 300, blank = True, null = True)
web_site = models.URLField(blank = True, null = True)
office_number = models.CharField(max_length = 20, blank = True, null = True)
class Employee(models.Model):
user = models.ForeignKey(User)
company = models.ForeignKey(User)
class Project(models.Model):
name = models.CharField(max_length = 100)
employees = models.ManyToManyField(Employee, through = 'EmployeeProject')
companies = models.ManyToManyField(Company)
class EmployeeProject(models.Model):
employee = models.ForeignKey(Employee)
project = models.ForeignKey(Project)
is_owner = models.BooleanField(default = False)
and in the view
# all of the projects for a user (assuming employee field is supposed to M2M to the Employee model
projects = Project.objects.filter(employees__user=request.user)
for project in projects :
# assuming that there was some connection between project and company (there isnt currently, see me list of bugs with your models)
for company in project.companies_set.all() :
# There is no employee model, but if there was
employees = company.employees_set.all()

Answer 3

I have pondered and used some of the solutions enlisted above, but nothing was exact to what I was looking for. For me the following piece of code works well
projects = Project.objects.filter(person = request.user)
user_projects = UserProject.objects.filter(project__in = projects)
for user_project in user_projects:
person = user_project.user.get_profile()
company.append(person.company)
people.append(person)
company = set(company)