的Django不能分配，“Rating.exercise”必须是“锻炼”的实例

Question

Localhost Screenshot 我有以下要求：

• 有练习和有收视率
• 的锻炼可以有多个等级

我的目标是动态地为练习添加评分，也就是说，我已经创建了所有练习，然后对特定练习进行评分，之后我应该可以添加一些功能。当我打“save_rating”鉴于我得到错误“不能分配‘[]’：‘Rating.exercise’必须是‘锻炼’实例。”

我在做什么错？

我的models.py看起来像下面

class Exercise(models.Model): 

#Field for storing exercise type 
EXERCISE_TYPE_CHOICES = (
    ('BS', 'Best stretch'), 
    ('BR', 'Butterfly reverse'), 
    ('SR', 'Squat row'), 
    ('PL', 'Plank'), 
    ('PU', 'Push up'), 
    ('SP', 'Side plank'), 
    ('SQ', 'Squat'), 
) 
exercise_type = models.CharField(max_length=5,choices=EXERCISE_TYPE_CHOICES) 
#Field for storing intensity level 
INTENSITY_LEVEL_CHOICES = (
    (1, 'Really simple'), 
    (2, 'Rather Simple'), 
    (3, 'Simple'), 
    (4, 'Okay'), 
    (5, 'Difficult'), 
    (6, 'Rather Difficult'), 
    (7, 'Really Difficult'), 
) 

intensity_level = models.IntegerField(choices=INTENSITY_LEVEL_CHOICES) 
#Field for storing video url for a particular exercise 
video_url = models.URLField() 
#Field for storing description of the exercise 
description = models.CharField(max_length=500) 


class Rating(models.Model): 

#Field for storing exercise type 
exercise = models.ForeignKey(Exercise, related_name='ratings', blank=True, null=True) 
#Field for storing rating 
RATING_CHOICES = (
    ('H', 'Happy'), 
    ('N', 'Neutral'), 
    ('S', 'Sad'), 
) 
value = models.CharField(max_length=1,choices=RATING_CHOICES) 

我定义我的串行类似以下内容：

class RatingSerializer(serializers.Serializer): 
class Meta: 
    model = Rating 
    fields = ('value') 

class ExerciseSerializer(serializers.Serializer): 
    pk = serializers.IntegerField(read_only=True) 
    exercise_type = serializers.CharField(required=True, allow_blank=False) 
    intensity_level = serializers.IntegerField(required=True) 
    video_url = serializers.URLField(required=True) 
    description = serializers.CharField(required=True, allow_blank=False) 
    ratings = RatingSerializer(many=True, read_only=True) 

我的观点：

def exercise_list(request): 
""" 
List all exercises. 
""" 
if request.method == 'GET': 
    exercises = Exercise.objects.filter(exercise_type='BS', intensity_level=1) 
    serializer = ExerciseSerializer(exercises, many=True) 
    return JSONResponse(serializer.data) 


def save_rating(request): 
""" 
Save a rating for a specific exercise. 
""" 
#Get a specific exercise for which you want to save the rating 
    specificExercise = Exercise.objects.filter(exercise_type='BS' , intensity_level=1) 

#Create a rating and pass the specific exercise reference to it 
    Rating.objects.create(exercise = specificExercise, value='H') 
    #serializer = ExerciseSerializer(rating, many=True) 
    serializer = ExerciseSerializer(instance=specificExercise) 
    return JSONResponse(serializer.data) 

Answer 1

在你的函数save_rating，你是将specificExercise作为查询集而不是一个Exercise instanc E，所以当你做：

Rating.objects.create(exercise=specificExercise, value='H') 

您尝试将查询集分配给您的exercise场，这当然是行不通的。

简单的修复将使用get而不是filter所以你有一个实例。但你也必须确保get查询不会抛出DoesNotExist异常，所以一个简单的try except会做。

编辑：

def save_rating(request): 
    """ 
    Save a rating for a specific exercise. 
    """ 
    # Get a specific exercise for which you want to save the rating 
    try: 
     specificExercise = Exercise.objects.get(exercise_type='BS', 
               intensity_level=1) 
     # Create a rating and pass the specific exercise reference to it 
     Rating.objects.create(exercise = specificExercise, value='H') 
     # serializer = ExerciseSerializer(rating, many=True) 
     serializer = ExerciseSerializer(instance=specificExercise) 
     return JSONResponse(serializer.data) 
    except Exercise.DoesNotExist: 
     # TODO: you need to return some error indication that there's no such exercise 
     return None 

请阅读有关making queries Django的文档。