MongoDB投影结果是否为所选项目的数组？
让我们创建一个包含文档的集合-
> db.demo151.insertOne({"ListOfNames":["Chris","David","Mike"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3513b6fdf09dd6d08539da")
}
> db.demo151.insertOne({"ListOfNames":["Mike","Bob"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3513c4fdf09dd6d08539db")
}
> db.demo151.insertOne({"ListOfNames":["John","David","Chris"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3513dcfdf09dd6d08539dc")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo151.find();
这将产生以下输出-
{ "_id" : ObjectId("5e3513b6fdf09dd6d08539da"), "ListOfNames" : [ "Chris", "David", "Mike" ] }
{ "_id" : ObjectId("5e3513c4fdf09dd6d08539db"), "ListOfNames" : [ "Mike", "Bob" ] }
{ "_id" : ObjectId("5e3513dcfdf09dd6d08539dc"), "ListOfNames" : [ "John", "David", "Chris" ] }以下是对投影结果的查询，作为所选项目的数组-
> db.demo151.distinct('_id', {'ListOfNames' : "Mike"});这将产生以下输出-
[
ObjectId("5e3513b6fdf09dd6d08539da"),
ObjectId("5e3513c4fdf09dd6d08539db")
]