检查mongodb中是否存在索引

问题描述

我是否可以通过mongo shell中的javascript使用一个命令，该命令可用于检查mongodb中是否存在特定的索引.我正在构建将创建索引的脚本文件.我希望如果我多次运行此文件，那么将不会重新创建已经存在的索引.

Is there a command that i can use via javascript in mongo shell that can be used to check if the particular index exists in my mongodb. I am building a script file that would create indexes. I would like that if I run this file multiple number of times then the indexes that already exists are not recreated.

我可以使用db.collection.getIndexes()获取数据库中所有索引的集合，然后构建一个逻辑来忽略已经存在的那些，但是我想知道是否有命令来获取索引，然后忽略创建索引的脚本.像这样:

I can use db.collection.getIndexes() to get the collection of all the indexes in my db and then build a logic to ignore the ones that already exists but i was wondering if there is command to get an index and then ignore a script that creates the index. Something like:

If !exists(db.collection.exists("indexname"))
{
    create  db.collectionName.CreateIndex("IndexName")
}

推荐答案

在MongoDB中创建索引是幂等操作.因此，运行db.names.createIndex({name:1})只会在索引不存在时创建索引.

Creating indexes in MongoDB is an idempotent operation. So running db.names.createIndex({name:1}) would create the index only if it didn't already exist.

createIndex()弃用的别名(从MongoDB 3.0开始)为 ensureIndex() ，这对于确实可以.

The deprecated (as of MongoDB 3.0) alias for createIndex() is ensureIndex() which is a bit clearer on what createIndex() actually does.

修改:感谢ZitRo在注释中进行了澄清，如使用.

Thanks to ZitRo for clarifying in comments that calling createIndex() with the same name but different options than an existing index will throw an error MongoError: Index with name: **indexName** already exists with different options as explained in this question.

如果您还有其他检查原因，则可以使用以下两种方法之一访问当前索引数据:

If you have other reasons for checking, then you can access current index data one of two ways:

1. 从v3.0开始，我们可以使用db.names.getIndexes()，其中names是集合的名称. 此处的文档.
2. 在v3.0之前，您可以访问system.indexes集合并按照下面所述进行操作find

1. As of v3.0, we can use db.names.getIndexes() where names is the name of the collection. Docs here.
2. Before v3.0, you can access the system.indexes collection and do a find as bri describes below.

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