ใช้ Aggregate Framework ร่วมกับ $group, $addToSet, $sum, $match เพื่อหาเอกสารซ้ำตามฟิลด์ที่กำหนด
ตัวอย่างการใช้งาน
สร้างคอลเลกชัน findDuplicateByKeyDemo:
> db.findDuplicateByKeyDemo.insertOne({"StudentId":1,"StudentName":"John"});
{ "acknowledged" : true, "insertedId" : ObjectId("5c7f5b168d10a061296a3c3a") }
> db.findDuplicateByKeyDemo.insertOne({"StudentId":2,"StudentName":"Carol"});
{ "acknowledged" : true, "insertedId" : ObjectId("5c7f5b1f8d10a061296a3c3b") }
> db.findDuplicateByKeyDemo.insertOne({"StudentId":3,"StudentName":"Carol"});
{ "acknowledged" : true, "insertedId" : ObjectId("5c7f5b248d10a061296a3c3c") }
> db.findDuplicateByKeyDemo.insertOne({"StudentId":4,"StudentName":"John"});
{ "acknowledged" : true, "insertedId" : ObjectId("5c7f5b2d8d10a061296a3c3d") }
> db.findDuplicateByKeyDemo.insertOne({"StudentId":5,"StudentName":"Sam"});
{ "acknowledged" : true, "insertedId" : ObjectId("5c7f5b398d10a061296a3c3e") }
> db.findDuplicateByKeyDemo.insertOne({"StudentId":6,"StudentName":"Carol"});
{ "acknowledged" : true, "insertedId" : ObjectId("5c7f5b438d10a061296a3c3f") }
แสดงข้อมูลทั้งหมด:
> db.findDuplicateByKeyDemo.find().pretty();
{"_id" : ObjectId("5c7f5b168d10a061296a3c3a"), "StudentId" : 1, "StudentName" : "John" }
{"_id" : ObjectId("5c7f5b1f8d10a061296a3c3b"), "StudentId" : 2, "StudentName" : "Carol" }
{"_id" : ObjectId("5c7f5b248d10a061296a3c3c"), "StudentId" : 3, "StudentName" : "Carol" }
{"_id" : ObjectId("5c7f5b2d8d10a061296a3c3d"), "StudentId" : 4, "StudentName" : "John" }
{"_id" : ObjectId("5c7f5b398d10a061296a3c3e"), "StudentId" : 5, "StudentName" : "Sam" }
{"_id" : ObjectId("5c7f5b438d10a061296a3c3f"), "StudentId" : 6, "StudentName" : "Carol" }
คำสั่ง Aggregate หาเอกสารซ้ำตาม StudentName:
> db.findDuplicateByKeyDemo.aggregate([
... { $group: {
... _id: { StudentName: "$StudentName" },
... UIDS: { $addToSet: "$_id" },
... COUNTER: { $sum: 1 }
... } },
... { $match: {
... COUNTER: { $gte: 2 }
... } },
... { $sort : { COUNTER : -1} },
... { $limit : 10 }
... ]).pretty();
{"_id" : {"StudentName" : "Carol"}, "UIDS" : [ ObjectId("5c7f5b248d10a061296a3c3c"), ObjectId("5c7f5b438d10a061296a3c3f"), ObjectId("5c7f5b1f8d10a061296a3c3b") ], "COUNTER" : 3 }
{"_id" : {"StudentName" : "John"}, "UIDS" : [ ObjectId("5c7f5b2d8d10a061296a3c3d"), ObjectId("5c7f5b168d10a061296a3c3a") ], "COUNTER" : 2 }
ผลลัพธ์แสดงชื่อที่ซ้ำ พร้อม _id ของเอกสารและจำนวนครั้งที่ซ้ำ
