根据数组集合中的值获取 _id 并插入到 mongodb 集合中

Question

输入：

[{"gradeName":1,"sectionName":"a","maximumStudents":12},{"gradeName":2,"sectionName":"b","maximumStudents":13}]

在mongodb中如何从两个集合中获取gradeName和sectionName的_id并存储在第三个集合中说mergeddetails

合并详情：

[{"grade_id":"60f819e04a9d43158cabad55","section_id":"60f819e04a9d43158cabad54","maximumStudents":12},{"grade_id":"60f819e04a9d43158cabad59","section_id":"60f819e04a9d43158cabad5b","maximumStudents":13}]

其中grade_id是对应gradeName的_id，section_id是对应sectionName的_id请帮助mongodb quire我正在使用nodejs编写API

Answer 1

您需要对这两个集合使用$lookup

db.student.aggregate([
  { $lookup: 
    { from: "grade", 
      localField: "gradeName", 
      foreignField: "grade", 
      as: "grade" 
    } 
  }, 
  {$lookup: 
    { from: "section", 
      localField: "sectionName", 
      foreignField: "section", 
      as: "section" 
    }
  },
  { $unwind: "$grade" },
  { $unwind: "$section" }, 
  {$project:
    {
      _id:0,
      "grade_id":"$grade._id",
      "section_id":"$section._id",
      maxStudent:1
    }
  }
])