Mongodb-在现有集合上添加唯一索引 [英] Mongodb- Add unique index on an existing collection

问题描述

我正在尝试在Mongodb中学习索引.我创建了一个数据库和一个集合，如下所示:

I am trying to learn indexing in Mongodb. I created a database and a collection as follows:

use mydb
db.createCollection("myFirstCollection")
one={name:"Helios"}
two={name:"Kepler"}
db.myFirstCollection.insert(one)
db.myFirstCollection.insert(two)

我能够列出以下结果:

db.myFirstCollection.find()
{ "_id" : ObjectId("53cde256f8807057b6bd827b"), "name" : "Helios" }
{ "_id" : ObjectId("53cde25bf8807057b6bd827c"), "name" : "kepler" }

我想在字段name上添加唯一索引.但是当我尝试时，出现以下错误

I want to add unique index on the field name. But when I tried, got the following error

db.myFirstCollection.ensureIndex({name:1},{unique:true})

{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 1,
        "ok" : 0,
        "errmsg" : "E11000 duplicate key error index: mydb.myFirstCollection.$name_1  dup key: { : null }",
        "code" : 11000
}

我无法弄清楚我在做什么.请帮忙.

I am unable to figure out the mistake what I am making. Please help.

推荐答案

请在此处查看缺少的字段部分: https://docs.mongodb.com/manual/core/index-unique/

Please see missing field section here: https://docs.mongodb.com/manual/core/index-unique/

您只能有一个不包含集合中存在的唯一索引的文档.

You can only have a single document that does not contain the unique index existing in the collection.

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