じゅう、构建评论系统

操作步骤：

创建模型保存评论内容
创建表单，从而可提交评论内容并对数据进行验证。
添加包含该表单的视图，并将最新的评论内容添加至数据库中。
标记帖子的详细模板，以显示评论列表和添加新评论的表单。

1. 创建模型

1.1 编辑blog应用程序的models.py文件，添加以下代码：

class Comment(models.Model):
    post = models.ForeignKey(Post,
                             on_delete=models.CASCADE,
                             related_name='comments')
    name = models.CharField(max_length=80)
    email = models.EmailField()
    body = models.TextField()
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    active = models.BooleanField(default=True)

    class Meta:
        ordering = ('-created',)

    def __str__(self):
        return "Comment by {} on {}.".format(self.name,self.post)

1.2. 同步到数据库

(my_env) zzx@zzx:~/mysite$ python manage.py makemigrations blog
输出如下：

Migrations for 'blog':
  blog/migrations/0002_comment.py
    - Create model Comment

(my_env) zzx@zzx:~/mysite$ python manage.py migrate
输出如下：

Operations to perform:
  Apply all migrations: admin, auth, blog, contenttypes, sessions
Running migrations:

1.3. 将新模型添加到管理站点中

from .models import Post,Comment

@admin.register(Comment)
class CommentAdmin(admin.ModelAdmin):
    list_display = ('name','email','post','created','active')
    list_filter = ('active','created','updated')

2. 创建模型中的表单

编辑blog应用程序的forms.py文件，并添加下列代码：

from .models import Comment

class CommentForm(forms.ModelForm):
    class Meta:
        model = Comment

针对CommentForm表单，仅需使用name、email和body字段——这些字段仅是用户可填写的字段。

3. 添加视图

编辑views.py文件，修改post_detail视图，如下所示：

from .models import Post,Comment
from .forms import EmailPostForm,CommentForm

def post_detail(request,year,month,day,post):
    post = get_object_or_404(Post,slug=post,
                                  status='published',
                                  publish__year=year,
                                  publish__month=month,
                                  publish__day=day)
    # List of active comments for this post
    comments = post.comments.filter(active=True)

    new_comment = None

    if request.method == 'POST':
        # A comment was posted
        comment_form = CommentForm(data=request.POST)
        if comment_form.is_valid():
            # Create Comment object but don't save to database yet
            new_comment = comment_form.save(commit=False)
            # Assign the current post to the comment
            new_comment.post = post
            # Save the comment to the database
            new_comment.save()
    else:
        comment_form = CommentForm()
    return render(request,
                  'blog/post/detail.html',
                  {'post':post,
                   'comments':comments,
                   'new_comment':new_comment,
                   'comment_form':comment_form})

4. 模板

使用post/detail.html模板执行下列操作：

显示帖子的全部评论数量
显示评论列表
向用户展示一个表单，并可添加新的评论内容

4.1 显示帖子的全部评论数量

    {% with comments.count as total_comments %}
    <h2>{{ total_comments }} comment{{ total_comments|pluralize }}</h2>
    {% endwith %}

4.2 显示评论列表

    {% for comment in comments %}
    <div class="comment">
      <p class="info">
        Comment {{ forloop.counter }} by {{ comment.name }} on
        {{ comment.created }}
      </p>
      {{ comment.body|linebreaks }}
    </div>
    {% empty %}
    <p>There are no comments yet.</p>
    {% endfor %}

4.3 向用户展示一个表单，并可添加新的评论内容

    {% if new_comment %}
      <h2>Your comment has been added.</h2>
    {% else %}
      <h2>Add a new comment</h2>
      <form action="." method="post">
        {{ comment_form.as_p }}
        {% csrf_token %}
        <p><input type="submit" value="Add comment"></p>
      </form>
    {% endif %}

最终效果如下：