在MongoDB中如何计算游标的迭代次数？
您需要在while循环和find()游标的帮助下使用自定义逻辑。让我们创建一个包含文档的集合-
> db.demo724.insertOne(
... {
... details:
... {
... id:101,
... otherDetails:[
... {Name:"Chris"}
... ]
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eab0cce43417811278f5890")
}
>
>
> db.demo724.insertOne(
... {
...
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eab0cce43417811278f5891")
}
> db.demo724.insertOne(
... {
... details:
... {
... id:1001
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eab0cce43417811278f5892")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo724.find();
这将产生以下输出＆miinus;。
{ "_id" : ObjectId("5eab0cce43417811278f5890"), "details" : { "id" : 101, "otherDetails" : [ { "Name" : "Chris" } ] } }
{ "_id" : ObjectId("5eab0cce43417811278f5891") }
{ "_id" : ObjectId("5eab0cce43417811278f5892"), "details" : { "id" : 1001 } }以下是在MongoDB中计算游标迭代的查询-
> var c=db.demo724.find();
> var detailsCount=0;
> while (c.hasNext()) {
... var current = c.next();
... if (typeof current["details"] != "undefined") {
... detailsCount++;
... }
... }
1
> print("number of details: " + detailsCount);这将产生以下输出-
number of details: 2