Django模型 - field_id是None，即使字段不是None，結果得到錯誤

Question

我收到一個錯誤，我不明白Django 1.3有關對象成員爲null的錯誤。該成員不是一個領域，它是一個領域的ID。

這是代碼。

模型：

class DirectorsIndividual(models.Model): 
    company = models.ForeignKey(CompanyUK) 
    director = models.ForeignKey(Director) 
    individual = models.ForeignKey(Individual) 

錯誤：

IntegrityError: mainapp_directorsindividual.director_id may not be NULL 

創建該對象的代碼：

link = DirectorsIndividual(company = co, 
          individual = individual, 
          director = officer) 

對象（略不相干的領域）的狀態：

link.director => <Director: Director object> 
link.director_id => None 
link.director.id => 3 
link.individual => <Individual: Individual object> 
link.individual.id => 2 

這裏發生了什麼？爲什麼董事個人對象沒有拿起分配給它的董事對象的ID？

[編輯：多個對象信息]

Answer 1

仔細檢查您在其中分配和保存對象的順序。這裏有一個超精簡例如：

from django.db import models 

class X(models.Model): 
    name = models.CharField(max_length=80) 

class Y(models.Model): 
    x = models.ForeignKey(X) 

這將導致完整性違規：

x = X() 
y = Y() 

x.name = 'test' 
y.x = x # At this moment, the pk has not yet been assigned. 

x.save() # Assigns the pk, but doesn't copy it over to the foreign key in y. 
y.save() # Bang.