如何使用mongo聚合将字符串转换为日期?

本文介绍了如何使用mongo聚合将字符串转换为日期?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

在一个收藏夹中，我存储了这种文档

In a collection, I store this kind of document

{ "_id" : 1, "created_at" : "2016/01/01 12:10:10", ... }. { "_id" : 2, "created_at" : "2016/01/04 12:10:10", ... }

我想通过使用聚合管道来查找具有"creared_at"> 2016/01/01的文档.

I would like to find documents have "creared_at" > 2016/01/01 by using aggregation pipeline.

任何人都可以将"created_at"转换为日期的解决方案，以便可以进行汇总吗?

Anybody have solution to convert "created_at" to date so can conpare in aggregation?

推荐答案

如前所述，您需要首先更改架构，以使created_at字段保留日期对象，而不是当前情况的字符串，然后您可以使用 find() 方法或聚合框架.前者将是最简单的方法.

As you have mentioned, you need to first change your schema so that the created_at field holds date objects as opposed to string as is the current situation, then you can query your collection either using the find() method or the aggregation framework. The former would be the most simple approach.

要将created_at转换为日期字段，您需要迭代 forEach() 方法，在循环内将created_at字段转换为Date对象，然后使用 运算符.

To convert created_at to date field, you would need to iterate the cursor returned by the find() method using the forEach() method, within the loop convert the created_at field to a Date object and then update the field using the $set operator.

充分利用 批量API

Take advantage of using the Bulk API for bulk updates which offer better performance as you will be sending the operations to the server in batches of say 1000 which gives you a better performance as you are not sending every request to the server, just once in every 1000 requests.

以下内容演示了这种方法，第一个示例使用MongoDB版本>= 2.6 and < 3.2中可用的Bulk API.它更新所有 通过将created_at字段更改为日期字段

The following demonstrates this approach, the first example uses the Bulk API available in MongoDB versions >= 2.6 and < 3.2. It updates all the documents in the collection by changing the created_at fields to date fields:

var bulk = db.collection.initializeUnorderedBulkOp(), counter = 0; db.collection.find({"created_at": {"$exists": true, "$type": 2 }}).forEach(function (doc) { var newDate = new Date(doc.created_at); bulk.find({ "_id": doc._id }).updateOne({ "$set": { "created_at": newDate} }); counter++; if (counter % 1000 == 0) { bulk.execute(); // Execute per 1000 operations and re-initialize every 1000 update statements bulk = db.collection.initializeUnorderedBulkOp(); } }) // Clean up remaining operations in queue if (counter % 1000 != 0) { bulk.execute(); }

下一个示例适用于新的MongoDB版本3.2，此版本自 弃用了批量API ，并使用 bulkWrite() :

The next example applies to the new MongoDB version 3.2 which has since deprecated the Bulk API and provided a newer set of apis using bulkWrite():

var cursor = db.collection.find({"created_at": {"$exists": true, "$type": 2 }}), bulkOps = []; cursor.forEach(function (doc) { var newDate = new Date(doc.created_at); bulkOps.push( { "updateOne": { "filter": { "_id": doc._id } , "update": { "$set": { "created_at": newDate } } } } ); if (bulkOps.length === 1000) { db.collection.bulkWrite(bulkOps); bulkOps = []; } }); if (bulkOps.length > 0) { db.collection.bulkWrite(bulkOps); }

架构修改完成后，您可以查询集合中的日期:

Once the schema modification is complete, you can then query your collection for the date:

var dt = new Date("2016/01/01"); db.collection.find({ "created_at": { "$gt": dt } });

如果您希望使用聚合框架进行查询，请运行以下管道以获取所需的结果.它使用 $match 运算符，与 find() 方法:

And should you wish to query using the aggregation framework, run the following pipeline to get the desired result. It uses the $match operator, which is similar to the find() method:

var dt = new Date("2016/01/01"); db.collection.aggregate([ { "$match": { "created_at": { "$gt": dt } } } ])