查询MongoDB中子文档的数组
要查询子文档数组，请在MongoDB中使用$unwind。让我们创建一个包含文档的集合-
> db.demo499.insertOne({
... "details":
... [
... {
... Name :"MIT",
... Rank: 1,
... "CountryName":"US"
... },
...
... {
... Name :"Stanford University",
... Rank: 2
... },
...
... {
... Name :"University of California, Berkeley",
... Rank: 3
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e87433d987b6e0e9d18f558")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo499.find();
{ "_id" : ObjectId("5e87433d987b6e0e9d18f558"), "details" : [ { "Name" : "MIT", "Rank" : 1,
"CountryName" : "US" }, { "Name" : "Stanford University", "Rank" : 2 }, { "Name" : "University
of California, Berkeley", "Rank" : 3 } ] }以下是如何查询子文档数组-
> db.demo499.aggregate({$unwind: "$details"},
... {$match: {"details.CountryName":{$exists: true}}},
... {$project: {"details.Name": 1, "details.CountryName": 1, "_id": 0}})这将产生以下输出-
{ "details" : { "Name" : "MIT", "CountryName" : "US" } }