mongoose查询所有分类下的文章总数

Question

const postSchema = mongoose.Schema({
  title: String,
  visit: {
    type: Number,
    default: 0
  },
  imagesrc: String,
  tags: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: 'tag'
    }
  ],
  category: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'category'
  },
  createTime: {
    type: Date,
    default: Date.now
  },
  lastEditTime: {
    type: Date,
    default: Date.now
  },
  hidden: Boolean,
  excerpt: String,
  content: String,
  comments: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: 'comment'
    }
  ]
}

const categorySchema = mongoose.Schema({
  name: String
}

文章和分类两个模型定义如上，文章schema有一个分类的外键，请问如何最高效率的查询出所有分类以及分类下的文章总数，返回一个集合

Answer 1

大概思路：

1、aggreate -- $group

 db.post.aggregate([
       {
            $group: {
                _id: $category,
                count: {$sum: 1}
            }
        }
    ])

2、forEach去关联到Category表

.forEach(function(doc){
                var cate = db.category.findOne({_id:doc._id});
                if (cate !== null) {
                doc.category_name = cate.name;
                }
                else {
                doc.category_name = 'not found';
                }
                db.resultSummary.insert(doc);
                })

效率需要查看执行计划具体分析。供参考