通过关键字段查找MongoDB集合中的所有重复文档？
使用聚合框架按关键字段查找MongoDB集合中的所有重复文档。
为了理解这个概念，让我们用文档创建一个集合。使用文档创建集合的查询如下-
> 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")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.findDuplicateByKeyDemo.find().pretty();
以下是输出-
{
"_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"
}这是查找所有重复文档的查询”-
> db.findDuplicateByKeyDemo.aggregate([
... { $group: {
... _id: { StudentName: "$StudentName" },
... UIDS: { $addToSet: "$_id" },
... COUNTER: { $sum: 1 }
... } },
... { $match: {
... COUNTER: { $gte: 2 }
... } },
... { $sort : { COUNTER : -1} },
... { $limit : 10 }
... ]).pretty();以下是显示重复记录的输出。在这里，学生“Carol”来了3次，而John则是2次-
以下是输出-
{
"_id" : {
"StudentName" : "Carol"
},
"UIDS" : [
ObjectId("5c7f5b248d10a061296a3c3c"),
ObjectId("5c7f5b438d10a061296a3c3f"),
ObjectId("5c7f5b1f8d10a061296a3c3b")
],
"COUNTER" : 3
}
{
"_id" : {
"StudentName" : "John"
},
"UIDS" : [
ObjectId("5c7f5b2d8d10a061296a3c3d"),
ObjectId("5c7f5b168d10a061296a3c3a")
],
"COUNTER" : 2
}