从MongoDB 4.2数据库中删除重复项 [英] Remove duplicates from MongoDB 4.2 data base

问题描述

我正在尝试从MongoDB中删除重复项，但是所有解决方案都失败了。
我的JSON结构：

I am trying to remove duplicates from MongoDB but all solutions find fail. My JSON structure:

{
    "_id" : ObjectId("5d94ad15667591cf569e6aa4"),
    "a" : "aaa",
    "b" : "bbb",
    "c" : "ccc",
    "d" : "ddd",
    "key" : "057cea2fc37aabd4a59462d3fd28c93b"

}

键值是md5（a + b + c + d）。
我已经有一个拥有超过10亿条记录的数据库，我想根据键并在使用唯一索引后删除所有重复项，因此如果键已在数据库中，则记录将不会再次插入。

Key value is md5(a+b+c+d). I already have a database with over 1 billion records and I want to remove all the duplicates according to key and after use unique index so if the key is already in data base the record wont insert again.

我已经尝试过

db.data.ensureIndex( { key:1 }, { unique:true, dropDups:true } )

但是对于我了解的内容，在MongoDB> 3.0中删除了dropDups

But for what I understand dropDups were removed in MongoDB > 3.0.

我也尝试了几种Java脚本代码，例如：

I tried also several of java script codes like:

var duplicates = [];

db.data.aggregate([
  { $match: { 
    key: { "$ne": '' }  // discard selection criteria
  }},
  { $group: { 
    _id: { key: "$key"}, // can be grouped on multiple properties 
    dups: { "$addToSet": "$_id" }, 
    count: { "$sum": 1 } 
  }}, 
  { $match: { 
    count: { "$gt": 1 }    // Duplicates considered as count greater than one
  }}
],
{allowDiskUse: true}       // For faster processing if set is larger
).forEach(function(doc) {
    doc.dups.shift();      // First element skipped for deleting
    doc.dups.forEach( function(dupId){ 
        duplicates.push(dupId);   // Getting all duplicate ids
        }
    )    
})

，但失败：

QUERY [Js] uncaught exception: Error: command failed: {
"ok": 0,
"errmsg" : "assertion src/mongo/db/pipeline/value.cpp:1365".
"code" : 8,
"codeName" : "UnknownError"
} : aggregate failed

我没有使用默认设置更改MongoDB设置。

I haven't change MongoDB settings, working with the default settings.

推荐答案

这是我的输入集合 dups ，其中包含一些重复的数据（ k 值 11 和 22 ）：

This is my input collection dups, with some duplicate data (k with values 11 and 22):

{ "_id" : 1, "k" : 11 }
{ "_id" : 2, "k" : 22 }
{ "_id" : 3, "k" : 11 }
{ "_id" : 4, "k" : 44 }
{ "_id" : 5, "k" : 55 }
{ "_id" : 6, "k" : 66 }
{ "_id" : 7, "k" : 22 }
{ "_id" : 8, "k" : 88 }
{ "_id" : 9, "k" : 11 }

查询将删除重复项：

db.dups.aggregate([
  { $group: { 
        _id: "$k",
        dups: { "$addToSet": "$_id" }, 
        count: { "$sum": 1 } 
  }}, 
  { $project: { k: "$_id", _id: { $arrayElemAt: [ "$dups", 0 ] } } }
] )
=>
{ "k" : 88, "_id" : 8 }
{ "k" : 22, "_id" : 7 }
{ "k" : 44, "_id" : 4 }
{ "k" : 55, "_id" : 5 }
{ "k" : 66, "_id" : 6 }
{ "k" : 11, "_id" : 9 }

如您所见，以下重复数据已删除：

{ "_id" : 1, "k" : 11 }
{ "_id" : 2, "k" : 22 }
{ "_id" : 3, "k" : 11 }

以数组形式获取结果：

var arr = db.dups.aggregate([ ...] ).toArray()

arr 具有文档数组：

[
        {
                "k" : 88,
                "_id" : 8
        },
        {
                "k" : 22,
                "_id" : 7
        },
        {
                "k" : 44,
                "_id" : 4
        },
        {
                "k" : 55,
                "_id" : 5
        },
        {
                "k" : 66,
                "_id" : 6
        },
        {
                "k" : 11,
                "_id" : 9
        }
]

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