查找一个字段与数组中另一个字段进行比较的文档

Find Documents Where a Field Compares with Another in an Array(查找一个字段与数组中另一个字段进行比较的文档)

问题描述

假设我有一组如下所示的文档:

<代码>{"_id" : ObjectId("5afa6df3a24cdb1652632ef5"),由...制作" : {_id":59232a1a41aa651ddff0939f"},所有者" : {_id":5abc4dc0f47f732c96d84aac"},acl":[{轮廓" : {_id":59232a1a41aa651ddff0939f"}},{轮廓" : {_id":5abc4dc0f47f732c96d84aac"}}]}

我想查找 createdBy._id != owner._id 的所有文档，以及 createdBy._id 出现在 中的条目之一的位置acl 数组.最终，我将要更新所有此类文档以将 owner._id 字段设置为等于 createdBy._id 字段.现在，我只是想弄清楚如何查询我想要更新的文档子集.

到目前为止，我想出了这个:

db.boards.find({$where: "this.createdBy._id != this.owner._id",$哪里:函数(){返回 this.acl.some(函数(e)=>{e.profile._id === this.createdBy._id}， 这);})

(我使用了 ES5 语法，以防 ES6 不行)

但是当我运行这个查询时，我得到了以下错误:

错误: 错误: { "ok" : 0, "errmsg" : "TypeError: e.profile is未定义 : _funcs2/<@:2:36 _funcs2@:2:12 ", "code" : 139 }

如何执行此查询/这里发生了什么?根据 docs 我读过.上面，e 应该是 acl 数组的一个元素，所以我希望它有一个字段 profile，但这似乎没有就是这样.

注意，我使用的是 Mongo 3.2，所以我不能使用 $expr，我已经看到一些资源表明这是一种可能性.

分辨率

事实证明，我对这个集合的架构做出了错误的假设.我遇到上述错误的原因是因为某些文档有一个 acl 数组，其中一个元素没有 profile 字段.下面的查询检查这种情况.它也有一个 $where，因为我最初编写它的方式(有两个)似乎最终给了我条件的 OR 而不是 AND.

db.boards.find({$哪里:函数(){返回 this.acl.some(函数(e)=>{e.profile !== 未定义 &&e.profile._id === this.createdBy._id &&this.createdBy._id != this.owner._id}， 这);})

您仍然可以在此处将 aggregate() 与 MongoDB 3.2 一起使用，但只需使用 $redact 改为:

db.boards.aggregate([{ "$ 编辑": {"$cond": {如果": {$和":[{ "$ne": ["$createdBy._id", "$owner._id" ] },{ "$setIsSubset": [["$createdBy._id"], "$acl.profile._id"] }]},"然后": "$$KEEP",其他":$$PRUNE"}}}])

或使用 $where 对于 MongoDB 3.2 shell，您只需要保留 this 的范围副本，并且您的语法有点偏离:

db.boards.find({$哪里":函数(){变种自我=这个；返回(this.createdBy._id ！= this.owner._id)&&this.acl.some(函数(e){返回 e.profile._id === self.createdBy._id})}})

或者在 ES6 兼容的环境中:

db.boards.find({$哪里":函数(){返回(this.createdBy._id ！= this.owner._id)&&this.acl.some(e => e.profile._id === this.createdBy._id)}})

聚合是两者中性能最高的选项，应该总是比使用 JavaScript 评估更可取

对于它的价值，使用 $ 的新语法expr 将是:

db.boards.find({"$expr": {$和":[{ "$ne": ["$createdBy._id", "$owner._id" ] },{ "$in": ["$createdBy._id", "$acl.profile._id"] }]}})

使用 $in优先于 $setIsSubset 其中语法稍微短一些.

注意 此处 JavaScript 比较有效的唯一原因是您错误地将 ObjectId 值存储为这些字段中的字符串".哪里有一个真实的"ObjectId 就像在 _id 字段中一样，比较需要从 valueOf() 中取字符串"比较顺序:

 返回 (this.createdBy._id.valueOf() != this.owner._id.valueOf())&&this.acl.some(e => e.profile._id.valueOf() === this.createdBy._id.valueOf())

<块引用>

没有它实际上是与 JavaScript 的对象比较"，而 { a: 1 } === { a: 1 } 实际上是 false.因此，避免这种复杂性是另一个原因有本机运算符来代替.

Let's say I have a collection of documents that look like this:

{
    "_id" : ObjectId("5afa6df3a24cdb1652632ef5"),
    "createdBy" : {
        "_id" : "59232a1a41aa651ddff0939f"
    },
    "owner" : {
        "_id" : "5abc4dc0f47f732c96d84aac"
    },
    "acl" : [
        {
            "profile" : {
                "_id" : "59232a1a41aa651ddff0939f"
            }
        },
        {
            "profile" : {
                "_id" : "5abc4dc0f47f732c96d84aac"
            }
        }
    ]
}

I want to find all documents where createdBy._id != owner._id, AND where the createdBy._id appears in one of the entries in the acl array. Eventually, I will want to update all such documents to set the owner._id field to equal the createdBy._id field. For now, I'm just trying to figure out how to query the subset of documents I want to update.

So far, I have come up with this:

db.boards.find({
  $where: "this.createdBy._id != this.owner._id", 
  $where: function() {
    return this.acl.some(
      function(e) => {
        e.profile._id === this.createdBy._id
      }, this);
  }
)

(I have used ES5 syntax just in case ES6 isn't ok)

But when I run this query, I get the following error:

Error: error: { "ok" : 0, "errmsg" : "TypeError: e.profile is undefined : _funcs2/<@:2:36 _funcs2@:2:12 ", "code" : 139 }

How do I perform this query / what is going on here? I would have expected my query to work, based on the docs I've read. Above, e should be an element of the acl array, so I expect it to have a field profile, but that doesn't seem to be the case.

Note, I'm using Mongo 3.2, so I can't use $expr, which I've seen some resources suggest is a possibility.

Resolution

It turns out that I had made an incorrect assumption about the schema of this collection. The reason I was running into the above error is because some documents have an acl array with an element that doesn't have a profile field. The below query checks for this case. It also has a single $where, because the way I had written it originally (with two) seemed to end up giving me an OR of the conditions instead of an AND.

db.boards.find({
  $where: function() {
    return this.acl.some(
      function(e) => {
        e.profile !== undefined && e.profile._id === this.createdBy._id && this.createdBy._id != this.owner._id
      }, this);
  }
)

You can still use aggregate() here with MongoDB 3.2, but just using $redact instead:

db.boards.aggregate([
  { "$redact": {
    "$cond": {
      "if": {
        "$and": [
          { "$ne": [ "$createdBy._id", "$owner._id" ] },
          { "$setIsSubset": [["$createdBy._id"], "$acl.profile._id"] }
        ]
      },
      "then": "$$KEEP",
      "else": "$$PRUNE"
    }
  }}
])

Or with $where for the MongoDB 3.2 shell, you just need to keep a scoped copy of this, and your syntax was a bit off:

db.boards.find({
  "$where": function() {
    var self = this;
    return (this.createdBy._id != this.owner._id)
      && this.acl.some(function(e) {
        return e.profile._id === self.createdBy._id
     })
  }
})

Or in an ES6 compatible environment then:

db.boards.find({
  "$where": function() {
    return (this.createdBy._id != this.owner._id)
      && this.acl.some(e => e.profile._id === this.createdBy._id)
  }
})

The aggregate is the most performant option of the two and should always be preferable to using JavaScript evalulation

And for what it's worth, the newer syntax with $expr would be:

db.boards.find({
  "$expr": {
    "$and": [
      { "$ne": [ "$createdBy._id", "$owner._id" ] },
      { "$in": [ "$createdBy._id", "$acl.profile._id"] }
    ]
  }
})

Using $in in preference to $setIsSubset where the syntax is a little shorter.

NOTE The only reason the JavaScript comparison here works is because you have mistakenly stored ObjectId values as "strings" in those fields. Where there is a "real" ObjectId just like in the _id field, the comparison needs to take the "string" from valueOf() in order to compare:

    return (this.createdBy._id.valueOf() != this.owner._id.valueOf())
      && this.acl.some(e => e.profile._id.valueOf() === this.createdBy._id.valueOf())

Without that it's actually an "Object Comparison" with JavaScript and { a: 1 } === { a: 1 } is actually false. So avoiding that complexity is another reason there are native operators for this instead.

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