Django cannot assign, "Rating.exercise" must be a "Exercise" instance - django

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I have following requirement:
There are exercises and there are ratings
An exercise can have multiple ratings
My goal is to add ratings to the exercises dynamically i.e. I have created all the exercises before hand and rating to a particular exercise I should be able add afterwards calling some function. When I hit 'save_rating' view I get the error "Cannot assign "[]": "Rating.exercise" must be a "Exercise" instance."
What am I doing wrong?
My models.py looks like following
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)
I have defined my serializer like following:
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)
My views:
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

In your function save_rating, you are having specificExercise as a queryset not one Exercise instance, so when you do:
Rating.objects.create(exercise=specificExercise, value='H')
You try to assign a queryset to your exercise field, which of course doesn't work.
Simple fix would be using get instead of filter so you got one instance. But you also have to make sure the get query doesn't throw DoesNotExist exception, so a simple try except would do.
Edit:
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
Please read django doc about making queries.