这是JSON文件。我想从名为courseSchedule
的数组_id: Zdhmwv5orgAd8pq54
返回元素的总数。
它应返回值:4
MongoDB查询是怎么样的?
{
"_id" : "Zdhmwv5orgAd8pq54",
"title" : "Learn ABC",
"courseSchedule" : [
{
"scheduleTitle" : "a",
"scheduleAuthor" : "a",
"id" : "93b817302efac52116794ec2"
},
{
"scheduleTitle" : "b",
"scheduleAuthor" : "b",
"id" : "7651b1954a24d7c5a8bd58e1"
},
{
"scheduleTitle" : "c",
"scheduleAuthor" : "c",
"id" : "43fbc406dca754596f8ea1d7"
},
{
"scheduleTitle" : "d",
"scheduleAuthor" : "d",
"id" : "43fbc406dca754596f8ea1d7"
},
]
}
嗨,谢谢你的帮助。我正在使用meteorhacks:聚合包Meteor.js app.Here是服务器端的代码。
var pipeline = [
{$project:
{courseSchedule:1, numberOfCourseSchedule:
{ $size: "$courseSchedule" }
}}];
let result = course.aggregate(pipeline);
console.log(result)
返回:[ { _id:'6CBXfkebKP2i9zxuZ', courseSchedule: [ [Object],[Object],[Object],[Object] ],numberOfCourseSchedule: 4} ]
我的下一个问题:如何访问属性NumberOfCourseSchedule以获取值4,因为我迟早需要增量计数器的这个数字。 感谢。