从MongoDB中的对象数组获取不同的值？
要从MongoDB中的对象数组获取不同的值，请使用distinct()。让我们创建一个包含文档的集合-
> db.demo442.insertOne(
... {
...
... "Information" : [
... {
... "FirstName" : "John",
... "Age" : 21
... },
... {
... "FirstName" : "Sam",
... "Age" : 23
... },
... {
... "FirstName" : "John",
... "Age" : 24
... },
... {
... "FirstName" : "Carol",
... "Age" : 20
... },
... {
... "FirstName" : "Sam",
... "Age" : 22
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e78cf29bbc41e36cc3caeb8")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo442.find();
这将产生以下输出-
{ "_id" : ObjectId("5e78cf29bbc41e36cc3caeb8"), "Information" : [ { "FirstName" : "John", "Age" : 21 }, { "FirstName" : "Sam", "Age" : 23 }, { "FirstName" : "John", "Age" : 24 }, { "FirstName" : "Carol", "Age" : 20 }, { "FirstName" : "Sam", "Age" : 22 } ] }以下是从MongoDB中的对象数组获取不同值的查询-
> db.demo442.distinct("Information.FirstName");这将产生以下输出-
[ "Carol", "John", "Sam" ]