如何仅显示在MongoDB中的数组中找到的元素？
要仅显示在数组中找到的元素，请使用aggregate()。让我们创建一个包含文档的集合-
> db.demo204.insertOne(
... {
... "_id" : 101,
... "Name" : "Chris",
... "Age" : 23,
... "details" : [
... {
... "id" : "1001",
... "empId" : "John_1001",
... "salary" : "50000",
... "Technology" : "Java"
... },
... {
... "id" : "1002",
... "empId" : "John_1002"
... },
... {
... "id" : "1003",
... "empId" : "John_10003",
... "salary" : "60000",
... "Technology" : "MongoDB"
... }
... ]
... }
...);
{ "acknowledged" : true, "insertedId" : 101 }在find()方法的帮助下显示集合中的所有文档-
> db.demo204.find();
这将产生以下输出-
{
"_id" : 101, "Name" : "Chris", "Age" : 23, "details" : [
{ "id" : "1001", "empId" : "John_1001", "salary" : "50000", "Technology" : "Java" },
{ "id" : "1002", "empId" : "John_1002" },
{ "id" : "1003", "empId" : "John_10003", "salary" : "60000", "Technology" : "MongoDB" }
]
}以下是仅显示在MongoDB中的数组中找到的元素的查询-
> db.demo204.aggregate(
... [
... { "$match": { "details.id": "1001" }},
... { "$unwind": "$details" },
... { "$match": { "details.id":"1001" }},
... { "$project": { "Technology": "$details.Technology", "_id":0 }}
... ]
...)这将产生以下输出-
{ "Technology" : "Java" }