MongoDB更新:根据现有字段生成新字段，或就地更新 [英] MongoDB update: Generate new field based on existing field, or update in place

问题描述

我已经搞混了一段时间，没有找到有关如何完成此任务的示例或说明.

I have been messing around with this for a while now and have found no examples nor explanations about how to accomplish this task.

我有一个文档集合，每个文档都有一个日期/时间字段.理想情况下，我需要为每个文档生成一个新字段，其中值基于来自日期/时间字段的时间，并添加了一个常数因子.

I have a collection of documents, each document has a date/time field. Ideally I need to generate a new field for each document where the value is based on the time from the date/time field with a constant factor added.

或者，仅更新适当的值就足够了.

Alternatively, simply updating the value in place would suffice.

我无法弄清楚如何在mongo shell更新语句中引用当前文档.

I have not been able to figure out how to reference the current document in a mongo shell update statement.

这是愚蠢的吗?我应该放弃并编写应用程序来完成看似简单的操作吗?

Is this folly? Should I give up and write an application do to complete this seemingly simple operation?

谢谢！

推荐答案

有时候，简单地写出问题即可带您解决. Kinda hacky，肯定很奇怪，但是似乎可以工作:

Sometimes simply writing the question out brings you to a solution. Kinda hacky, and definitely weird, but seems to work:

db.actuals.find().forEach(
    function(d) { 
        var dt = d.date; 
        var ndt = new Date(d.date).setHours(dt.getHours() - 8); 
        db.actuals.update( {_id: d._id}, { $set: { local: new Date(ndt) } } );
    }
)

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