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python - 查询相关对象的列值并存储为变量

问题描述

我试图name在我的模型Category中获取与我的模型相关联的列的值Post。我想将 的值保存name到变量中以备后用。我试过print(post.categories.name)了，但它返回 value None。post.categories.values()我可以通过运行which 返回来确认有一个实际值<QuerySet [{'id': 1, 'name': 'General'}]>

模型：

from django.db import models



class Category(models.Model):
    name = models.CharField(max_length=30)

class Post(models.Model):
    title = models.SlugField(max_length = 250, null = True, blank = True)
    body = models.TextField()
    created_on = models.DateTimeField(null=True)
    last_modified = models.DateTimeField(null=True)
    categories = models.ManyToManyField('Category', related_name='posts')

class Comment(models.Model):
    author = models.CharField(max_length=60)
    body = models.TextField()
    created_on = models.DateTimeField(auto_now_add=True)
    post = models.ForeignKey('Post', on_delete=models.CASCADE)

意见：

def blog_detail(request, pk):
    post = Post.objects.select_related().get(pk=pk)
    category = post.categories.name # This returns None but should return General
    form = CommentForm()
    if request.method == 'POST':
        form = CommentForm(request.POST)
        if form.is_valid():
            comment = Comment(
                author=form.cleaned_data["author"],
                body=form.cleaned_data["body"],
                post=post
            )
            comment.save()

    comments = Comment.objects.filter(post=post)
    context = {
        "post": post,
        "comments": comments,
        "form": form,
    }
    return render(request, "blog_detail.html", context)

标签： pythondjango

解决方案

你不能。您在模型上定义categories为 a ，因此a获取类别并返回与关联的所有类别。ManyToManyFieldPostpost.categoriesModelManagerpost.categories.all()post

您可以像这样获取帖子类别的名称列表：

category_names = [category.name for category in post.categories.all()]

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