Mongo查找不包含给定值的文档(使用$ not)

问题描述

我在MongoDB中有两项:

{'title':'active item',
 'tags':[
        {'tag':'active'},
        {'tag':'anothertag'}
]}
{'title':'completed item',
 'tags':[
        {'tag':'completed'}
]}

它可以查找标记为已完成的项目:

db.items.find({'tags.tag':'completed'})
RESULT: [<completed item>]

现在，我想选择所有未标记为已完成的项目，所以我尝试:

db.items.find({$not:{'tags.tag':'completed'}})
DESIRED RESULT: [<active item>]
ACTUAL RESULT: []

但是以某种方式，这不会返回任何结果.显然，我在Mongo中误解了$ not，但是为什么呢?如何查询以查找标记中未包含给定值的记录?

解决方案

$not 运算符必须是运算符表达式，而不是字段/值对象.

因此，parvin的答案是执行此操作的最简单方法，但仅出于学习目的，您可以使用$not支持的表达式，例如

{'title':'active item',
 'tags':[
        {'tag':'active'},
        {'tag':'anothertag'}
]}
{'title':'completed item',
 'tags':[
        {'tag':'completed'}
]}

来实现此目的:

 db.items.find({tags: {$not: {$elemMatch: {tag: 'completed'}}}})

db.items.find({'tags.tag': {$not: /completed/}})
 

I have two items in MongoDB:

{'title':'active item',
 'tags':[
        {'tag':'active'},
        {'tag':'anothertag'}
]}
{'title':'completed item',
 'tags':[
        {'tag':'completed'}
]}

It works to find items which are tagged as completed:

db.items.find({'tags.tag':'completed'})
RESULT: [<completed item>]

Now, I want to select all items which are not tagged as completed, so I tried:

db.items.find({$not:{'tags.tag':'completed'}})
DESIRED RESULT: [<active item>]
ACTUAL RESULT: []

But somehow this doesn't return any results. Clearly I misunderstand $not in Mongo, but why? How do I query to find the records that do not contain a given value in their tags?

解决方案

The target of the $not operator needs to be an operator-expression, not a field/value object.

So parvin's answer is the easiest way to do this, but just for learning purposes, you can do this with $not by using $not supported expressions like:

db.items.find({tags: {$not: {$elemMatch: {tag: 'completed'}}}})

db.items.find({'tags.tag': {$not: /completed/}})

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