Question

(x, y)

如何在java中编写此查询?????在这里，学生是收集字段rollno，名称和标记，我必须根据他们的滚动数字找到学生的百分比。我无法编写用于添加标记的代码，因为添加运算符不支持添加多个值。

Answer 1

这似乎有效。还有其他构建器模式/便利，但这暴露了所有工作。并为丰富的动态建筑留出空间。

        DBCollection coll = db.getCollection("student");

        List<DBObject> pipe = new ArrayList<DBObject>();

        /**                                                                          
         *  Clearly, lots of room for dynamic behavior here.                         
         *  Different sets of marks, etc.  And the divisor is                        
         *  the length of these, etc.                                                
         */
        String[] marks = new String[]{"$marks1","$marks2","$marks3"};
        DBObject add = new BasicDBObject("$add", marks);
        List l2 = new ArrayList();
        l2.add(add);
        l2.add(marks.length); // 3                                                   
        DBObject divide = new BasicDBObject("$divide", l2);

        DBObject prjflds = new BasicDBObject();
        prjflds.put("rollno", 1);
        prjflds.put("per", divide);

        DBObject project = new BasicDBObject();
        project.put("$project", prjflds);
        pipe.add(project);

        AggregationOutput agg = coll.aggregate(pipe);

        for (DBObject result : agg.results()) {
            System.out.println(result);
        }

如何使用java驱动程序在mongoDB中添加两个字段

1 个答案: