java中的mongodb问题与限制和排序

Question

收藏:progs

{ "_id" : "ABC", "defaultDirectory" : "abc", "defaultRecvDirectory" : "abc" }
{ "_id" : "RAS", "defaultRecvDirectory" : "recv/ras" }
{ "_id" : "SND", "defaultSendDirectory" : "send/snd" }

在 mongo 控制台中:

db.progs.find({"_id":{"$lt":"ZZZZZZZZZ"}}).sort({"_id":-1}).limit(1);

==>    { "_id" : "SND", "defaultSendDirectory" : "send/snd" }

在 Java 中:

    BasicDBObject query = new BasicDBObject();
    query.put("_id", new BasicDBObject("$lt", "ZZZZZZZZZZ"));
    DBCursor cursor = collection.find(query).sort(new BasicDBObject("_id","-1")).limit(1);
    for (DBObject dbObject : cursor) {
        System.out.println(dbObject);
    }

==>    { "_id" : "ABC", "defaultSendDirectory" : "abc", "defaultRecvDirectory" : "abc" }

谁能解释一下区别？

Answer 1

从您的排序中的 "-1" 中删除引号:

DBCursor cursor = collection.find(query).sort(new BasicDBObject("_id",-1)).limit(1);

或者使用 com.mongodb.operation.OrderBy 中的 Mongodb ASC/DESC 常量，而不是硬编码 1/-1

例子:

DBCursor cursor = collection.find(query).sort(new BasicDBObject("_id", OrderBy.DESC.getIntRepresentation())).limit(1);