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[英]Django: Database used for prefetch_related is not the same that the parent query
[英]Django - objects.values() and prefetch_related() in same query
我有如下的Book,Profile,Book_stat模型。 我试图最小化Book
模型和prefetch_related方法中的字段以从Book_stat
模型中获取数据。
models.py
class Book(models.Model):
title = models.CharField(max_length=200)
image = models.FileField(upload_to="mp/", blank=True)
def __str__(self):
return self.title
class Profile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
full_name = models.CharField(max_length=150)
def __str__(self):
return self.full_name
class Book_stat(models.Model):
user = models.ForeignKey(User)
book = models.ForeignKey(Book)
rating = models.DecimalField(max_digits=5, decimal_places=2, default=Decimal('0.00'))
like = models.BooleanField(default=False)
def __str__(self):
return self.book.title + ' by: ' + self.user.profile.full_name
views.py
def books(request):
books = books = Book.objects.prefetch_related('book_stat_set').values('id','title', 'image')
for book in books:
for book_stat in book.book_stat_set.all(): # error: 'dict' object has no attribute 'book_stat_set'
book.stats = book_stat
pprint(vars(book_stat))
return HttpResponse(books, content_type= 'json')
1)我想将json response
发送到前端,如下所示
2)如果可能的话我想用book_stat_set.values('like', 'rating')
而不是book_stat_set.all()
这样对我的查询like
, rating
只
books = [
{
id: 1,
title: 'some title1',
image: 'image1.jpg',
stats: {
like: true,
rating: 3.50
}
},
{
id: 2,
title: 'some title2',
image: 'image1.jpg',
stats: {
like: true,
rating: 3.50
}
}
]
相反,您可以only
使用values
方法并手动进行序列化:
from django.db.models import Prefetch
from django.forms import model_to_dict
from django.http import JsonResponse
def books(request):
prefetch = Prefetch('book_stat_set', queryset=Book_stat.objects.only('like', 'rating'))
qs = Book.objects.prefetch_related(prefetch).only('id','title', 'image')
result = []
for book in qs:
row = model_to_dict(book, fields=['id','title', 'image'])
row['image'] = row['image'].url
stats = []
for book_stat in book.book_stat_set.all():
stat = model_to_dict(book_stat, fields=['like', 'rating'])
stat['rating'] = str(stat['rating']) # or float(stat['rating']) - depends on your purposes
stats.append(stat)
# you can calculate an average rating here
row['stats'] = stats
result.append(row)
return JsonResponse(result)
如果只需要一次,则可以手动对其进行序列化。
books = Book.objects.prefetch_related('book_stat_set')
books_json = [{
'id': book.id,
'title': book.title,
'image': book.image.url,
'stats': [
{
'like': stat.like, 'rating': str(stat.rating)
} for stat in book.book_stat_set.all()
]
} for book in books]
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