优化子属性中$ exists的查询 [英] optimizing query for $exists in sub property

问题描述

我需要搜索另一个对象内是否存在属性. 该集合包含如下文档:

I need to search for the existence of a property that is within another object. the collection contains documents that look like:

"properties": {
    "source": {
        "a/name": 12837,
        "a/different/name": 76129
    }
}

如下所示，查询字符串的一部分来自变量.

As you can see below, part of the query string is from a variable.

在JohnnyHK的帮助下(请参见 mongo查询-属性是否存在?更多信息)，我通过执行以下操作获得了一个查询:

With some help from JohnnyHK (see mongo query - does property exist? for more info), I've got a query that works by doing the following:

var name = 'a/name';
var query = {};
query['properties.source.' + name] = {$exists: true};
collection.find(query).toArray(function...

现在，我需要查看是否可以对集合进行索引以提高此查询的性能.

Now I need to see if I can index the collection to improve the performance of this query.

我不知道如何执行此操作，甚至不知道是否可以为此编制索引.

I don't have a clue how to do this or if it is even possible to index for this.

建议?

推荐答案

这里发生了2件事.

首先，您可能正在寻找稀疏索引.

First probably you are looking for sparse indexes.

http://docs.mongodb.org/manual/core/index-sparse /

在您的情况下，它可能是"properties.source.a/name"字段上的稀疏索引.在字段上建立索引将大大缩短查询查找时间.

In your case it could be a sparse index on "properties.source.a/name" field. Making indexes on field will dramatically improve your query lookup time.

db.yourCollectionName.createIndex( { "properties.source.a/name": 1 }, { sparse: true } )

第二件事.总是在您想知道查询是快速还是慢速时，使用mongo console，运行查询及其结果调用explain方法.

Second thing. Always when you want to know whether your query is fast/slow, use mongo console, run your query and on its result call explain method.

db.yourCollectionName.find(query).explain(); 多亏了它，您将知道查询是否使用索引，完成查询必须检查多少文档以及其他一些有用的信息.

db.yourCollectionName.find(query).explain(); Thanks to it you will know whether your query uses indexes or not, how many documents it had to check in order to complete query and some others useful information.

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