Django模型设计：如何实现用户与内容之间的独立状态管理（以点赞为例）

# models.py (在你的应用中)
from django.db import models
from django.contrib.auth import get_user_model

User = get_user_model()

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    author = models.ForeignKey(User, on_delete=models.CASCADE)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        return self.title

# models.py (在你的应用中)
from django.db import models
from django.contrib.auth import get_user_model
# 假设 Post 模型已定义在同一个文件或可导入
from .models import Post 

User = get_user_model()

class PostLike(models.Model):
    """
    表示用户对文章的点赞记录。
    """
    user = models.ForeignKey(User, on_delete=models.CASCADE, verbose_name="点赞用户")
    post = models.ForeignKey(Post, on_delete=models.CASCADE, related_name='likes', verbose_name="被点赞文章")
    timestamp = models.DateTimeField(auto_now_add=True, verbose_name="点赞时间")

    class Meta:
        # 确保一个用户只能点赞同一篇文章一次
        unique_together = ('user', 'post')
        verbose_name = "文章点赞"
        verbose_name_plural = "文章点赞"

    def __str__(self):
        return f"{self.user.username} 点赞了 {self.post.title}"

from django.contrib.auth import get_user_model
from .models import Post, PostLike # 假设 Post 和 PostLike 在同一个 models.py 中

User = get_user_model()

# 假设我们已经获取了用户和文章实例
# user_instance = User.objects.get(id=1)
# post_instance = Post.objects.get(id=1)
# 为了演示，我们先创建一些示例数据
try:
    user1 = User.objects.get_or_create(username='user1')[0]
    user2 = User.objects.get_or_create(username='user2')[0]
    post1 = Post.objects.get_or_create(title='Django教程', content='...', author=user1)[0]
    post2 = Post.objects.get_or_create(title='Python基础', content='...', author=user2)[0]
except Exception as e:
    print(f"创建用户或文章失败: {e}")
    user1, user2, post1, post2 = None, None, None, None # 防止后续代码出错

if user1 and post1:
    print(f"\n--- 演示用户 {user1.username} 和文章 {post1.title} 的操作 ---")

    # 1. 用户点赞一篇文章
    try:
        PostLike.objects.create(user=user1, post=post1)
        print(f"用户 {user1.username} 成功点赞文章 '{post1.title}'")
    except Exception as e:
        # 如果用户已点赞，unique_together 约束会抛出 IntegrityError
        print(f"用户 {user1.username} 尝试点赞文章 '{post1.title}' 失败或已点赞: {e}")

    # 2. 判断用户是否点赞了某篇文章
    is_liked_by_user1 = PostLike.objects.filter(user=user1, post=post1).exists()
    print(f"用户 {user1.username} 是否点赞了文章 '{post1.title}': {is_liked_by_user1}")

    # 另一种判断方式，利用 post 模型的 related_name
    is_liked_by_user1_via_related_name = post1.likes.filter(user=user1).exists()
    print(f"通过 related_name 判断用户 {user1.username} 是否点赞了文章 '{post1.title}': {is_liked_by_user1_via_related_name}")

    # 3. 取消用户对某篇文章的点赞
    try:
        like_record = PostLike.objects.get(user=user1, post=post1)
        like_record.delete()
        print(f"用户 {user1.username} 成功取消点赞文章 '{post1.title}'")
    except PostLike.DoesNotExist:
        print(f"用户 {user1.username} 未点赞文章 '{post1.title}'，无法取消")

    # 再次检查点赞状态
    is_liked_after_unlike = PostLike.objects.filter(user=user1, post=post1).exists()
    print(f"取消点赞后，用户 {user1.username} 是否点赞了文章 '{post1.title}': {is_liked_after_unlike}")

    # 4. 获取某篇文章的点赞总数
    # 先让 user2 点赞 post1
    if user2:
        try:
            PostLike.objects.create(user=user2, post=post1)
            print(f"用户 {user2.username} 成功点赞文章 '{post1.title}'")
        except Exception as e:
            print(f"用户 {user2.username} 尝试点赞文章 '{post1.title}' 失败或已点赞: {e}")

    like_count = post1.likes.count()
    print(f"文章 '{post1.title}' 的点赞总数: {like_count}")

    # 5. 获取某用户点赞过的所有文章
    # 让 user1 再次点赞 post1，并点赞 post2
    try:
        PostLike.objects.create(user=user1, post=post1)
        PostLike.objects.create(user=user1, post=post2)
        print(f"用户 {user1.username} 再次点赞文章 '{post1.title}' 并点赞文章 '{post2.title}'")
    except Exception as e:
        print(f"用户 {user1.username} 尝试点赞失败: {e}")

    # 注意：如果 PostLike 模型中没有为 user 字段指定 related_name，
    # 默认的反向关系管理器是 user_instance.postlike_set
    liked_posts_by_user1 = [like.post for like in user1.postlike_set.all()]
    print(f"用户 {user1.username} 点赞过的文章: {[p.title for p in liked_posts_by_user1]}")