如何加入查询3个表和Django

Question

models.py

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

    # emp_no first_name last_name 
     ------ ---------- ---------- 
     10005 Christian Erde 

class DeptEmp(models.Model): 
    emp_no = models.ForeignKey(Employee, on_delete=models.CASCADE) 
    dept_no = models.ForeignKey(Department, on_delete=models.CASCADE) 

    # dept_no_id emp_no_id 
     ---------- ---------- 
     d003  10005  

class Department(models.Model): 
    dept_no = models.CharField(primary_key=True, max_length=4) 
    dept_name = models.CharField(unique=True, max_length=40) 

    # dept_no  dept_name  
     ---------- --------------- 
     d003  Human Resources 

views.py

class EmpList(ListView): 
    queryset = Employee.objects.all().select_related('deptemp').select_related('department') 

employee_list.html

{% for emp in object_list %} 
    {{ emp.first_name }} 
    {{ emp.last_name }} 
    {{ emp.department.dept_name }} 
{% endfor %} 

我得到这个错误信息的浏览器：在select_related中给出的无效字段名 ：'deptemp'，'department'。选择是：（无）

Answer 1

“select_related”

返回一个QuerySet，将“跟随”外键关系。

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) 

然后Book.objects.select_related（ 'author__hometown'）

为了您exmaples打电话：

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 %}