无法删除帖子评论：接口返回成功但数据库未删除

我认为控制器中的删除评论函数逻辑无误，但调用接口后，Postman返回"Comment deleted successfully!"，然而数据库内的评论仍存在，未被删除。请帮忙排查代码问题。

路由代码 #

router.delete("/:id/comment/:cid", protectRoute, deleteComment);

控制器代码 #

const deleteComment = async(req, res) => {
try {
    const post = await Post.findById(req.params.id);

    const comment = post.comments.find(
        (comment) => comment._id.toString() === req.params.cid.toString()
    );

    if(!comment){
        return res.status(404).json({ error: "Comment not found!" });
    }

    if(comment.userId.toString() !== req.user._id.toString()){
        return res.status(401).json({ error: "Unauthorized to delete comment" });
    }

    if (comment.userId.toString() === req.user._id.toString()) {
        post.comments = post.comments.filter(
            ({ id }) => id !== req.params.cid
        );
    }
        await post.save();
    
        return res.status(200).json({ message: "Comment deleted successfully!" });
} catch (err) {
    res.status(500).json({ error: err.message });
}
};

Post模型代码 #

import mongoose from "mongoose";
const ObjectId = mongoose.Types.ObjectId;

const postSchema = mongoose.Schema({
    postedBy: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User',
        required: true
    },
    text: {
        type: String,
        maxLength: 500
    },
    img: {
        type: String,
    },
    video: {
        type: String,
        ref: "Upload"
    },
    likes: [{
        // 存储用户ID数组
        type: mongoose.Schema.Types.ObjectId,
        ref: "User",
        default: []
    }],
    saves: [{
        // 存储用户ID数组
        type: mongoose.Schema.Types.ObjectId,
        ref: "User",
        default: []
    }],
    comments: [
        {
            id: {
                type: ObjectId,
            },
            userId: {
                type: mongoose.Schema.Types.ObjectId,
                ref: "User",
                required: true
            },
            text: {
                type: String,
                required: true
            },
            likes: [{
                // 存储用户ID数组
                type: mongoose.Schema.Types.ObjectId,
                ref: "User",
                default: []
            }],
            userProfilePic: {
                type: String,
            },
            username: {
                type: String
            },
            date: {
                type: Date,
                default: Date.now()
            },
            replies: [{
                id: {
                    type: ObjectId,
                },
                userId: {
                    type: mongoose.Schema.Types.ObjectId,
                    ref: "User",
                    required: true
                },
                text: {
                    type: String,
                    required: true
                },
                userProfilePic: {
                    type: String,
                },
                username: {
                    type: String
                },
                date: {
                    type: Date,
                    default: Date.now()
                }
            }]
        }
    ]
}, {timestamps: true}
)

const Post = mongoose.model('Post', postSchema);

export default Post;

问题排查与修复 #

核心问题出在评论过滤时的类型不匹配，以及查找逻辑的字段一致性问题：

1. 字段匹配不一致：控制器中查找评论时用了comment._id，但你的Post模型里评论子文档的业务标识是自定义的id字段。虽然MongoDB子文档默认会生成_id，但你接口传参的cid对应的是自定义id，所以查找逻辑应该改为匹配comment.id。

2. 类型比较错误：过滤评论时，id是ObjectId类型，而req.params.cid是字符串类型，直接用!==比较永远为true，导致没有评论被过滤。需要将id转为字符串后再和cid比较。

3. 冗余判断：前面已经判断过comment.userId !== req.user._id时会返回权限错误，后面的if (comment.userId.toString() === req.user._id.toString())判断完全多余，可以直接执行过滤逻辑。

修复后的控制器代码：

const deleteComment = async(req, res) => {
try {
    const post = await Post.findById(req.params.id);

    // 改为匹配自定义的id字段
    const comment = post.comments.find(
        (comment) => comment.id.toString() === req.params.cid.toString()
    );

    if(!comment){
        return res.status(404).json({ error: "Comment not found!" });
    }

    if(comment.userId.toString() !== req.user._id.toString()){
        return res.status(401).json({ error: "Unauthorized to delete comment" });
    }

    // 去掉冗余判断，直接过滤，同时将id转为字符串比较
    post.comments = post.comments.filter(
        (comment) => comment.id.toString() !== req.params.cid.toString()
    );
    
    await post.save();
    
    return res.status(200).json({ message: "Comment deleted successfully!" });
} catch (err) {
    res.status(500).json({ error: err.message });
}
};

另外，建议你在创建评论时确保id字段被正确赋值为新的ObjectId，否则查找和过滤逻辑会失效。比如创建评论时：

// 示例：添加评论时的id赋值
post.comments.push({
    id: new mongoose.Types.ObjectId(),
    userId: req.user._id,
    text: req.body.text,
    // 其他字段...
});

内容的提问来源于stack exchange，提问作者khayal