MongoDB:聚合具有静态值的$ project add字段 [英] MongoDB: aggregate $project add field with static value

问题描述

我可以以某种方式添加具有静态(未计算)值的自定义字段吗?

Can I somehow add custom field with static (not computed) value?

我想在发送之前准备对象，并且需要删除一些带有内部信息的字段并添加带有某些实体ID的字段.

I want to prepare objects before send and I need to remove some fields with internal information and add field with some entity ID.

例如，我有类似这样的对象的测试"集合

For example I have collection "test" with objects like this

{_id: ObjectId(...), data: {...}}

我需要将其转换为

{data: {...}, entity_id: 54}

那么如何在不循环生成代码的情况下添加entity_id:54?

So how can I add entity_id: 54 without looping over result in my code?

db.test.aggregate({ $project: {_id: 0, data: 1, entity_id: ? } })

谢谢

推荐答案

请注意，$ literal是在Mongo 2.6中实现的. 所以现在您可以简单地编写:

Note that $literal was implemented in Mongo 2.6. So now you can simply write:

db.test.aggregate(
   {$project: {_id: 0, data: 1, entity_id: {$literal: 54}}})

请参见 $ literal .

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