Django一些功能

一、

往queryset里每一个对象添加新属性

如下两个model

class Comment(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, verbose_name="评论者id")
    article = models.ForeignKey(Article, on_delete=models.CASCADE, verbose_name="文章id")
    parent_comment = models.ForeignKey("self", on_delete=models.CASCADE, null=True, verbose_name="父评论")
    content = models.TextField(verbose_name="评论内容")
    comment_time = models.DateTimeField(auto_now_add=True, verbose_name="评论时间")
    is_deleted = models.SmallIntegerField(default=0, verbose_name="是否已删除")

    class Meta:
        ordering = ["-comment_time"]

class CommentFeedBack(models.Model):
    comment = models.ForeignKey(Comment, verbose_name="评论id", on_delete=models.CASCADE)
    user = models.ForeignKey(User, verbose_name="用户id", on_delete=models.CASCADE)
    feed_back = models.SmallIntegerField(verbose_name="反馈", help_text="0-未评 1-好评 2-差评")

获取每个评论及其好评与差评数
comments = Comment.objects.filter(article_id=id)
for comment in comments:
    comment.good_view = CommentFeedBack.objects.filter(comment_id=comment.id, feed_back=1).count()
    comment.bad_view = CommentFeedBack.objects.filter(comment_id=comment.id, feed_back=2).count()

二、字段改名

from django.db.models import F

query_set.values(new_name=F(old_name))


例如：
有如下model
class Category(models.Model):
    name = models.CharField(max_length=20, verbose_name='类名')
    is_deleted = models.SmallIntegerField(default=0, verbose_name='是否已删除')

class Article(models.Model):
    title = models.CharField(max_length=120, verbose_name='标题')
    category = models.ForeignKey(Category, verbose_name='分类', on_delete=models.CASCADE)
    add_time = models.DateTimeField(auto_now_add=True, verbose_name='添加时间')
    is_deleted = models.SmallIntegerField(default=0, verbose_name='是否已删除',
                                          help_text='0-未删除 1-已删除')

Article.objects.filter(is_deleted=0).values(category_name=F("category__name"))
即可将category__name这个不好看的名字改为category_name

但是有个问题是如果只是获取一条数据，使用model.objects.get()操作是不能使用values操作的，此时可以像如下进行获取:
Article.objects.filter(id=164).values(category_name=F("category__name"))[0]
或者
Article.objects.filter(id=164).values(category_name=F("category__name")).first()

三、将查询的数据按其中某一个字段分组

如下model
class ActionGroup(models.Model):
    group = models.CharField(max_length=32, verbose_name='动作组名')

    class Meta:
        verbose_name = "动作组表"
        verbose_name_plural = verbose_name

class Right(models.Model):
    url = models.CharField(max_length=32, verbose_name='路由')
    action = models.CharField(max_length=32, verbose_name='名称')
    type = models.CharField(max_length=8, verbose_name='请求方式')
    action_group = models.ForeignKey(ActionGroup, verbose_name='动作组', on_delete=models.CASCADE)


按动作组即action_group对权限进行分组，此时要用到defaultdict
from collections import defaultdict

rights = Right.objects.all().values("id", "action_group_id", "action_group__group", "action")
res = defaultdict(list)
for right in rights:
    res[right['action_group_id']].append((right['id'], right['action_group__group'], right['action']))

defaultdict是当没有这个key是自动添加，list说明它的key是一个list.
将res返回给前端时记得dict(res)一下。

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