django - get() 返回了多个主题

Question

当我试图将一个属性与另一个具有M 到M 关系的属性相关联时，我收到此错误:

get() returned more than one topic -- it returned 2!

你们能告诉我这是什么意思吗？也许可以提前告诉我如何避免这个错误？

模型

class LearningObjective(models.Model):
    learning_objective=models.TextField()

class Topic(models.Model):
    learning_objective_topic=models.ManyToManyField(LearningObjective)
    topic=models.TextField()

LearningObjective.objects.all() 的输出

[<LearningObjective: lO1>, <LearningObjective: lO2>, <LearningObjective: lO3>]

Topic.objects.all() 的输出

[<Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>, <Topic: Topic object>]

观看次数

 def create_themen(request):
     new_topic=Topic(topic=request.POST['topic'])
     new_topic.save()
     return render(request, 'topic.html', {'topic': topic.objects.all()})

 def create_learning_objective(request):
     new_learning_objective=LearningObjective(learning_objective=request.POST['learning_objective'])
     new_learning_objective.save()
     new_learning_objective_topic=Topic.objects.get(topic=request.POST['topic'])
     new_learning_objective_topic.new_learning_objective_topic.add(new_learning_objective)
     return render( request, 'learning_objective.html', {
                    'topic': Topic.objects.all(),
                    'todo': TodoList.objects.all(),
                    'learning_objective': LearningObjective.objects.all()
                  })

Answer 1

get() returned more than one topic -- it returned 2!

上述错误表明您在使用 get() 查询时传递的特定参数相关的数据库中有多个记录。比如

Model.objects.get(field_name=some_param)

为避免将来出现此类错误，您始终需要根据您的模式设计进行查询。 在您的情况下，您设计了一个带有 many-to-many relationship 的表所以显然该字段会有多个记录，这就是您收到上述错误的原因。

因此，您应该使用 filter() 而不是使用 get()这将返回多个记录。比如

Model.objects.filter(field_name=some_param)

请阅读如何在 Django 中进行查询 here .