如何使用猫鼬查询文件？

Question

我正在使用Mongoose用res_persons查找_id嵌套数据。但是它没有返回one array，而是返回all。这是代码和文档。

{
    "documents": [],
    "_id": "5d283957a9450309383aa349",
    "event_name": "Main",
    "res_persons": [
        {
            "_id": "5d283957a9450309383aa34b",
            "name": "John",
            "desig": "Software Developer"
        },
        {
            "_id": "5d283957a9450309383aa34a",
            "name": "Jane",
            "desig": "Data Analyst"
        }
    ],
    "outcomes": [],
    "__v": 0
}

现在，如果我触发此查询，

var query = {  "res_persons": { $elemMatch:{_id:"5d283957a9450309383aa34a"} }  };

//I also tried this but output is same.
//var query = {  "res_persons._id": "5d283957a9450309383aa34a"  };

return await this.eventModel.findOne(query).select("res_persons.name");

它返回此：

{
    "_id": "5d283957a9450309383aa349",
    "res_persons": [
        {
            "name": "John"
        },
        {
            "name": "Jane"
        }
    ]
}

如果我专心_id:"5d283957a9450309383aa34a"，它应该只返回John。为什么显示Jane？

我在这里做错什么了吗？请纠正我。

谢谢！