Converting raw SQL to Django QuerySet API

Question

Model

class Person(models.Model):
    GENDER = (
    ('M','Male'),
    ('F','Female'),
    )
    first_name = models.CharField("First Name", max_length=100)
    last_name = models.CharField("Last Name",max_length=100)
    middle_name = models.CharField("Middle Name", max_length=100, blank=True)
    suffix_name = models.ManyToManyField(SuffixName, verbose_name="Suffix Name",null=True, blank=True) 
    gender = models.CharField(max_length=1, choices=GENDER)
    department = models.ManyToManyField(Department, verbose_name="Department",null=True, blank=True) 

    def __unicode__(self):
        return (u'%s') % (self.last_name.upper() + ', ' + self.first_name + ' ' + self.middle_name)

class Department(models.Model):
    department_desc = models.CharField('Department', max_length=100,unique=True)
    department_acronym = models.CharField('Department Acronym', max_length=20,blank=True,help_text="Add acronym if any, not required")
    location = models.CharField('Location',max_length=100,blank=True)
    localnumber = models.CharField('Local Number',max_length=30,blank=True)
    active = models.BooleanField('Active',default=True)

    def __unicode__(self):
        return self.department_desc

How can I convert this raw SQL to a Django query?

SELECT pp.first_name, pd.department_desc, pd.localnumber
FROM person_person as pp 
INNER JOIN person_person_department as ppd on pp.id = ppd.person_id
INNER JOIN person_department as pd on pd.id = ppd.department_id 

Answer 1

Use QuerySet.values or QuerySet.values_list:

Person.objects.values('first_name', 'department__department_desc', 'department__localnumber')
# -> Returns a ValuesQuerySet that yields dictionaries when iterated.

Person.objects.values_list('first_name', 'department__department_desc', 'department__localnumber')
# -> Returns a ValuesQuerySet that yields tuples when iterated.

Answer 2

Fetching on Person will automatically fetch the related objects, so your query is:

people = Person.objects.all()

Then, you can do the following:

for person in people:
  print('Person: {0}'.format(person.first_name))
  for dept in person.department_set.all():
      print('Desc: {0}, Local Number: {1}'.format(dept.department_desc,
                                                  dept.localnumber))

If you want to restrict the returned values, use values_list.