我正在尝试查询mongodb集合以获取一个特定的id字段-

问题描述

我正在尝试从具有匹配的"EmployeeName"的最后更新("timeSliceStart")行中获取_id

I am trying to get _id from last updated("timeSliceStart") row which has matching "EmployeeName"

DBCursor cursor = collection.find(EmployeeName).sort(new BasicDBObject("timeSliceStart", -1)).limit(1);
 while(cursor.hasNext()) {
            String result = cursor.next().get("id"); }

Mongo DB中的数据::

Data in Mongo DB::

{ "_id" : { "employeeId" : "1234567890", "@objectName" : "FeedMetadata" }, "school" : false, "college" : null, "errorCount" : 0, "errors" : [], "EmployeeName" : "Peter"}

{ "_id" : { "employeeId" : "1234567890", "@objectName" : "FeedMetadata" }, "school" : false, "college" : null, "errorCount" : 0, "errors" : [], "EmployeeName" : "Peter"}

正在打印的结果是:{ "employeeId" : "1234567890" , "@objectName" : "FeedMetadata"}

The result that is getting printed is :{ "employeeId" : "1234567890" , "@objectName" : "FeedMetadata"}

我只想要_id中的employeeId，我尝试了_id.employeeId ;，但是它返回了null.有没有办法只显示employeeId?

I want just the employeeId from _id, I tried _id.employeeId ;, but it returned null.Is there a way to display only the employeeId?

我的Java程序-

  BasicDBObject whereQuery = new BasicDBObject();
    whereQuery.put("EmployeeName", empName);
    DBCursor cursor = collection.find(whereQuery).sort(new BasicDBObject("lastUpdate", -1)).limit(1);
    while(cursor.hasNext()) {
        String result = cursor.next().get("_id").toString();
        System.out.println(result);
    }

推荐答案

您可以像这样更改while循环:

You can change the while loop like this:

while(cursor.hasNext()) {
    String result = ((HashMap)((BasicDBObject)(cursor.next().get("_id")))).get("employeeId");
    System.out.println(result);
}

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