How to join 3 tables in query with Django

Question

models.py

class Employee(models.Model):
    emp_no = models.IntegerField(primary_key=True)
    first_name = ...
    last_name = ...

    # emp_no first_name  las         


        

Answer 1

"select_related"

Returns a QuerySet that will “follow” foreign-key relationships.

from django.db import models
class City(models.Model):
    # ...
    pass
class Person(models.Model):
    # ...
    hometown = models.ForeignKey(
        City,
        on_delete=models.SET_NULL,
        blank=True,
    null=True,
    )

class Book(models.Model):
    # ...
    author = models.ForeignKey(Person, on_delete=models.CASCADE)

then a call to Book.objects.select_related('author__hometown')

For your exmaples:

class EmpList(ListView):
    queryset = DeptEmp.objects.all().select_related('emp_no').select_related('dept_no')

employee_list.html

{% for deptemp in object_list %}
    {{ deptemp.emp_no.first_name }}
    {{ deptemp.emp_no.last_name }}
    {{ deptemp.dept_no.dept_name }}
{% endfor %}