在对象数组上使用 Mongoose/MongoDB $addToSet 功能 [英] Using Mongoose / MongoDB $addToSet functionality on array of objects

问题描述

假设我在 Mongoose 模式上有这个数组属性('articles'):

say I have this array property ('articles') on a Mongoose schema:

articles: [ 

 {
  kind: 'bear',
  hashtag: 'foo'    
 },

 {
  kind: 'llama',
  hashtag: 'baz',
  },

 {
  kind: 'sheep',
  hashtag: 'bar',
  }

]

如何使用

$addToSet https://docs.mongodb.org/manual/reference/operator/update/addToSet/

通过检查 hashtag 的值来添加到这个数组中以查看它是否唯一?

to add to this array by checking the value of hashtag to see if it's unique?

例如，如果我想将以下对象添加到上述数组中，我希望 Mongo 将其拒绝"为重复项:

For example, if I want to add the following object to the above array, I want Mongo to 'reject' it as a duplicate:

{
  kind: 'tortoise',
  hashtag: 'foo'

}

因为 hashtag=foo 已经被占用了.

because hashtag=foo has already been taken.

问题是我只知道如何将 $addToSet 与简单的整数数组一起使用...

The problem is that I only know how to use $addToSet with simple arrays of integers...

例如，如果文章看起来像这样:

for example, if articles looked like this:

articles: [ 1 , 5 , 4, 2]

我会像这样使用 $addToSet:

I would use $addToSet like this:

var data = {

    "$addToSet": {
     "articles": 9
   }

}

model.update(data);

但是我怎样才能用唯一字段是字符串的对象数组完成同样的事情，在这种情况下是'hashtag'?文档没有说明这一点，似乎我到处搜索..

but how can I accomplish the same thing with an array of objects where the unique field is a string, in this case 'hashtag'? The docs don't make this clear and it seems like I have searched everywhere..

谢谢

推荐答案

您需要使用 $ne 运算符.

You need to use the $ne operator.

var data = { 'kind': 'tortoise', 'hashtag': 'foo' };
Model.update(
    { 'articles.hashtag': { '$ne': 'foo' } }, 
    { '$addToSet': { 'articles': data } }
)

只有在article"数组中没有hashtag值为foo"的子文档时，才会更新文档.

This will update the document only if there is no sub document in the "article" array with the value of hashtag equals to "foo".

正如评论中提到的@BlakesSeven

As @BlakesSeven mentioned in the comment

$addToSet 变成一旦您测试其中一个值的存在，则无关紧要，因此这也可能是 $push 代码清晰.但原则是正确的，因为 $addToSet 适用于整个对象，而不仅仅是其中的一部分.

The $addToSet becomes irrelevant once you are testing for the presence of one of the values, so this may as well be a $push for code clarity. But the principle is correct since $addToSet works on the whole object and not just part of it.

Model.update({ 
    { 'articles.hashtag': { '$ne': 'foo' } }, 
    { '$push': {'articles':  data } }
)

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