查找一个字段与数组中另一个字段进行比较的文档

本文介绍了查找一个字段与数组中另一个字段进行比较的文档的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

假设我有一组如下所示的文档:

{"_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);})

解决方案

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())

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); } )

解决方案

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.