MongoDB - 如何查询集合中的嵌套项？
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MongoDB - how to query for a nested item inside a collection?
提问by Genadinik
I have some data that looks like this:
我有一些看起来像这样的数据：
[
{
"_id" : ObjectId("4e2f2af16f1e7e4c2000000a"),
"advertisers" : [
{
"created_at" : ISODate("2011-07-26T21:02:19Z"),
"category" : "Infinity Pro Spin Air Brush",
"updated_at" : ISODate("2011-07-26T21:02:19Z"),
"lowered_name" : "conair",
"twitter_name" : "",
"facebook_page_url" : "",
"website_url" : "",
"user_ids" : [ ],
"blog_url" : "",
},
and I was thinking that a query like this would give the id of the advertiser:
我在想这样的查询会给出广告商的 ID：
var start = new Date(2011, 1, 1);
> var end = new Date(2011, 12, 12);
> db.agencies.find( { "created_at" : {$gte : start , $lt : end} } , { _id : 1 , program_ids : 1 , advertisers { name : 1 } } ).limit(1).toArray();
But my query didn't work. Any idea how I can add the fields inside the nested elements to my list of fields I want to get?
但是我的查询没有用。知道如何将嵌套元素内的字段添加到我想要获取的字段列表中吗？
Thanks!
谢谢！
回答by lnmx
Use dot notation (e.g. advertisers.name) to query and retrieve fields from nested objects:
使用点符号（例如advertisers.name）从嵌套对象中查询和检索字段：
db.agencies.find({
"advertisers.created_at": {
$gte: start,
$lt: end
}
},
{
_id: 1,
program_ids: 1,
"advertisers.name": 1
}
}).limit(1).toArray();
Reference: Retrieving a Subset of Fieldsand Dot Notation
回答by Mak Ashtekar
db.agencies.find(
{ "advertisers.created_at" : {$gte : start , $lt : end} } ,
{ program_ids : 1 , advertisers.name : 1 }
).limit(1).pretty();
回答by Mak Ashtekar
There is one thing called dot notation that MongoDB provides that allows you to look inside arrays of elements. Using it is as simple as adding a dot for each array you want to enter.
MongoDB 提供了一种叫做点表示法的东西，它允许您查看元素数组的内部。使用它就像为要输入的每个数组添加一个点一样简单。
In your case
在你的情况下
"_id" : ObjectId("4e2f2af16f1e7e4c2000000a"),
"advertisers" : [
{
"created_at" : ISODate("2011-07-26T21:02:19Z"),
"category" : "Infinity Pro Spin Air Brush",
"updated_at" : ISODate("2011-07-26T21:02:19Z"),
"lowered_name" : "conair",
"twitter_name" : "",
"facebook_page_url" : "",
"website_url" : "",
"user_ids" : [ ],
"blog_url" : "",
},
{ ... }
If you want to go inside the array of advertisers to look for the property created_at inside each one of them, you can simply write the query with the property {'advertisers.created_at': query} like follows
如果您想进入广告客户数组以查找每个广告客户中的属性 created_at，您可以简单地使用属性 {' Advertisingrs.created_at': query}编写查询，如下所示
db.agencies.find( { 'advertisers.created_at' : { {$gte : start , $lt : end} ... }
