text: const mongoose = require('mongoose');
  
  const postSchema = new mongoose.Schema({
    title: { type: String },
    body: { type: String },
    categories: [{ type: mongoose.SchemaTypes.objectId, ref: 'Category' }],	// 关联多个Category
  })
  
  const Post = mongoose.model('Post', postSchema)
  module.exports = Post