Mongoose Virtual - 计算本地引用数组中另一个模型中的引用

Question

我有 2 个模型Comment 和 Report。

const mongoose = require('mongoose');

const CommentSchema = new mongoose.Schema(
    {
        content: {
            type: String,
            trim: true,
            maxLength: 2048,
        },
        createdAt: {
            type: Date,
            default: Date.now,
        },
        parent: {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'Comment',
            required: false,
        },
        replies: [
            {
                type: mongoose.Schema.Types.ObjectId,
                ref: 'Comment',
            },
        ],
        isReply: {
            type: Boolean,
            default: false,
        },
    },
    { toJSON: { virtuals: true }, toObject: { virtuals: true } }
);

CommentSchema.virtual('reportCount', {
    ref: 'Report',
    localField: '_id',
    foreignField: 'comment',
    justOne: false,
    count: true,
});

CommentSchema.virtual('reportReplyCount', {
    ref: 'Report',
    localField: 'replies',
    foreignField: 'comment',
    justOne: false,
    count: true,
});

module.exports = mongoose.model('Comment', CommentSchema);

Comment 具有字段回复，它是指向 Comment 模型的引用数组。用户可以报告评论，当发生这种情况时，新的报告文档会存储在报告集合中，并且它包含对该评论的引用和对用户的引用。我在评论架构中有 2 个虚拟属性，reportCount（显示该评论的报告数量）和 reportReplyCount（显示评论回复的报告数量）。现在 reportCount 可以完美运行，但 reportReplyCount 却不行。当我创建评论以及对该评论的回复时，它会显示回复数量而不是报告数量。我用谷歌搜索但找不到类似的东西。

const mongoose = require('mongoose');
    
    const ReportSchema = new mongoose.Schema({
        description: {
            type: String,
            trim: true,
            required: true,
            maxLength: 100,
        },
        reporter: {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'User',
            required: true,
        },
        createdAt: {
            type: Date,
            default: Date.now,
        },
        comment: {
            type: mongoose.Schema.Types.ObjectId,
            ref: 'Comment',
            required: true,
        },
    });
    
    
    module.exports = mongoose.model('Report', ReportSchema);

Answer 1

我不知道你到底想做什么，但我环顾四周，似乎没有任何现有的解决方案。虚拟是解决问题的一种方法，但我还没有看到在这种情况下使用它的答案。

您可以尝试创建一个名为 reportReplyCount 的新虚拟，以显示回复报告的数量。然后在评论中使用aggregate 并将reportCount 替换为新的虚拟。您可以使用以下内容：

CommentSchema.virtual('reportReplyCount', {
    ref: 'Report', // reference to Report model
    localField: 'replies', // matches field Comment Schema has named 'replies' 
    foreignField: 'comment', // matches field Report Schema has named 'comment' (foreign key in Report model) 
    justOne: false, // this is going to return all related documents, not just one (just like reportCount)  
    count: true, // set it to true so it returns a number instead of an array of documents  
});

    CommentSchema.methods = { ... }

    CommentSchema.statics = { ... }

     module.exports = mongoose.model('Comment', CommentSchema);

如果您能为您的问题找到另一种解决方案，我会避免在您的情况下使用虚拟机。

顺便说一句，我看到开发人员创建了一个新模型来充当虚拟模型，如下所示：

const mongoose = require('mongoose');

   const ReportSchema = new mongoose.Schema({
       description: {
           type: String,
           trim: true,
           required: true,
           maxLength: 100,
       },
       reporter: { // reference to User model (foreign key) 
           type: mongoose.Schema.Types.ObjectId, 
           ref: 'User',  // reference to User model (foreign key) 

   });

   module.exports = mongoose.model('Report', ReportSchema);

   // Now you need an instance of that new Schema called VirtualReport. The schema must follow the same format as the "real" Report's schema did above but with a few extra parameters that refer to the virtual and it's definition (as in how it will behave). 

   const VirtualReportSchema = new mongoose.Schema({ ... }, { _id : false });

   module.exports = mongoose.model('VirtualReport', VirtualReportSchema);

那么你需要做的就是，在你的架构中有虚拟：

   // Now you can use VirtualReport like any other model. It will work just like Report but it won't get stored in the database. 
   CommentSchema.virtual('reportReplyCount', {
       ref: 'VirtualReport', // reference to VirtualReport model 
       localField: 'replies', // matches field Comment Schema has named 'replies' 
       foreignField: 'comment', // matches field VirtualReport Schema has named 'comment' (foreign key in VirtualReport model) 
       justOne: false, // this is going to return all related documents, not just one (just like reportCount)  
       count: true, // set it to true so it returns a number instead of an array of documents  
   });

   CommentSchema.methods = { ... }

   CommentSchema.statics = { ... }

    module.exports = mongoose.model('Comment', CommentSchema);

但请注意，虚拟的定义（“它将如何表现”）必须包含设置为 false 的 _id 属性（否则将引发错误）。这是因为当子文档中使用虚拟对象并且用户通过点符号（例如，commentToBeDeleted[parent].reportReplyCount）引用它们时，点符号会尝试访问虚拟的 _id 属性。如果它设置为 false，点表示法将无法找到该虚拟，并且您将收到错误消息。所以不要忘记将_id属性设置为false！

顺便说一句，有人问过这个问题here。不幸的是，这个问题是在 Stack Overflow 上提出的，而不是在 MongoDB 自己的文档中提出的，其中提供了对虚拟的解释的链接（还有关于“justOne”的评论，但至少它直接引用了文档）。