在MongoDB数据库中的对象数组上按_id查找？
要通过_id在对象数组上查找，请使用汇总，并避免使用find()。首先让我们创建一个包含文档的集合-
> db.demo414.insertOne(
... {
... "_id": "110",
... "details":[
... {
... "StudentName":"John",
... "StudentMarks":56
... },
... {
... "StudentName":"Robert",
... "StudentMarks":98
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : "110" }在find()方法的帮助下显示集合中的所有文档-
> db.demo414.find();
这将产生以下输出-
{ "_id" : "110", "details" : [ { "StudentName" : "John", "StudentMarks" : 56 }, { "StudentName" : "Robert", "StudentMarks" : 98 } ] }以下是通过_id在对象数组上查找的查询-
> db.demo414.aggregate([{$unwind: "$details"}, {$match:{"details.StudentMarks" :56}}] )这将产生以下输出-
{ "_id" : "110", "details" : { "StudentName" : "John", "StudentMarks" : 56 } }