请问MongoDB java 如何使用类似$substr的操作符

Question

请问MongoDB java 如何使用类似$substr的操作符

Answer 1

有人需要的话自己体会。这是我自己想到的方法，也许还有更好的。

BasicDBObject my_time = new BasicDBObject();
my_time.append("$substr",new Object[]{ "$in_time",8,2});
DBObject time = new BasicDBObject();
time.put("my_time", my_time);
DBObject project = new BasicDBObject().append("$project",time);

Answer 2

BasicDBObject object1 = new BasicDBObject().apend("name","Tom");
BasicDBObject object2 = new BasicDBObject("$set", new BasicDBObject("age",20));
collection.update( object1 , object2 );