Select * 在 mongo 中

Question

我收到了这个查询：

User.collection.aggregate([
      {"$project" => {
        "dayOfMonth" => {"$dayOfMonth" => "$created_time"},
        "month" => {"$month" => "$created_time"},
        "year" => {"$year" => "$created_time"},
      }},
      {"$group" => {
        "_id" => { "dayOfMonth" => "$dayOfMonth", "month" => "$month", "year" => "$year"},
        "Total" => {"$sum" => 1}
      }},
      {"$sort" => {
        "created_at" => -1
      }}
    ])

我的用户 table 有我需要的用户名和全名，

我做了类似的事情

User.collection.aggregate([
          {"$project" => {
            "dayOfMonth" => {"$dayOfMonth" => "$created_at"},
            "month" => {"$month" => "$created_at"},
            "year" => {"$year" => "$created_at"},
            "username" => "$username"
          }},
          {"$group" => {
            "_id" => { "dayOfMonth" => "$dayOfMonth", "month" => "$month", "year" => "$year"},
            "Total" => {"$sum" => 1}
          }},
          {"$sort" => {
            "created_at" => -1
          }}
        ])

但它不起作用并给出与上面相同的结果，不打印用户名，有什么想法吗？我的目标是在按创建日期分组后获取用户名。

Answer 1

User.collection.aggregate([
          {"$project" => {
            "dayOfMonth" => {"$dayOfMonth" => "$created_at"},
            "month" => {"$month" => "$created_at"},
            "year" => {"$year" => "$created_at"},
            "username" => "$username"
          }},
          {"$group" => {
            "_id" => { "dayOfMonth" => "$dayOfMonth", "month" => "$month", "year" => "$year"},
            "Total" => {"$sum" => 1},
            "username" => {"$first" => "$username"}
          }},
          {"$sort" => {
            "created_at" => -1
          }}
        ])

Select * 在 mongo 中

Select * in mongo id

ruby-on-rails

mongoid