Question

我正在尝试使用以下代码构建一个简单的mongodb数据库查找。在运行时，代码运行但从不返回值。

生成的查询在命令行中工作没问题。数据库非常大，大约2.8gb。

public static void main(String[]args){

        String customer="peter";
        String job="builder";


        // To connect to mongodb server
        MongoClient mongoClient=new MongoClient("localhost",27017);

        // Now connect to your databases
        MongoDatabase db=mongoClient.getDatabase("customers");
        System.out.println("Connect to database successfully");

        // Now connect to your collection
        MongoCollection<Document> collection=db.getCollection("customerData");
        System.out.println("Connect to collection");

        BasicDBObject andQuery=new BasicDBObject();
        List<BasicDBObject> obj=new ArrayList<BasicDBObject>();

        obj.add(new BasicDBObject("job",job));
        obj.add(new BasicDBObject("customer",customer));
        andQuery.put("$and",obj);

        System.out.println(andQuery.toString());

        FindIterable<Document> iterable=collection.find(new Document(andQuery));
        MongoCursor<Document> iterableDocument=iterable.iterator();

        while(iterableDocument.hasNext()){
          Document wholeDocument=(Document)iterableDocument.next();
          System.out.println("1: "+wholeDocument.get("age"));
          System.out.println("2: "+wholeDocument.get("dob"));
        }
}

Answer 1

尝试将查询简化为

DBObject obj = new BasicDBObject();
 obj.put( "job", job );
 obj.put( "customer", customer );
collection.find(new Document(obj))

此外，getDatabase和getCollection不进行连接。如果拼错了这些部分，查询将不返回任何内容，因为您正在访问空数据库。（第一次连接尝试是当你调用'find'时。如果数据库或集合不存在，Mongo会在你写入时创建它）

Mongodb Java查询永远不会返回值

1 个答案: