如何通过密钥名称从mongoDB中检索一个值？

Question

我是mongoDB的新手。我正在使用java和mongoDB。我喜欢json，

[{ "_id" : { "$oid" : "4ceb753a70fdf877ef5113ca"} , "HomeTown" : "AA" , 
"PhoneNumber" : { "CustName" : "xxx" , "Number" : "3403290"},
"MobileNumber" : { "CustName" : "yyy" , "Number" : "9323304302"}}]

    [{ "_id" : { "$oid" : "4ceb753a70fdf877ef5113ca"} , "HomeTown" : "AA" , 
"PhoneNumber" : { "CustName" : "xxx" , "Number" : "3403290"},
"MobileNumber" : { "CustName" : "yyy" , "Number" : "9323304302"}}]

    [{ "_id" : { "$oid" : "4ceb753a70fdf877ef5113ca"} , "HomeTown" : "BB" , 
"PhoneNumber" : { "CustName" : "xxx" , "Number" : "3403290"},
"MobileNumber" : { "CustName" : "yyy" , "Number" : "9323304302"}}]

    [{ "_id" : { "$oid" : "4ceb753a70fdf877ef5113ca"} , "HomeTown" : "BB" , 
"PhoneNumber" : { "CustName" : "xxx" , "Number" : "3403290"},
"MobileNumber" : { "CustName" : "yyy" , "Number" : "9323304302"}}]

在一个集合中，所有文档都有不同的HomeTown，我只知道密钥名称HomeTown，我如何获得HomeTown值？

在mongo网站中，我可以找到find()和findOne()。

谢谢！

Answer 1

find()就足够了。

db.CollectionName.find({},{HomeTown:1})

在java中，它将是：

BasicDBObject query = new BasicDBObject();
BasicDBObject field = new BasicDBObject();
field.put("HomeTown", 1);
DBCursor cursor = db.getCollection(collectionName).find(query,field);
while (cursor.hasNext()) {
    BasicDBObject obj = (BasicDBObject) cursor.next();
    result.add(obj.getString("HomeTown"));
}

Answer 2

 db.CollectionName.find({},{HomeTown:1,PhoneNumber:0}) 

会错，但

 db.CollectionName.find({},{HomeTown:1, _id:0}) 

是正确的，因为你需要明确地压制_id。仅供参考。

Answer 3

Mongo m = new Mongo('localhost',27017);
DB db = m.getDB("yourDBName");
Collection coll = db.getCollection("yourCollectionName")
BasicDBObject query = new BasicDBObject();
query.put("HomeTown", 1);
DBCursor cursor = coll.find(query);
ArrayList arr = new ArrayList();
String str;
while (cursor.hasNext()) {
    str=cursor.curr().get("HomeTown").toString();
    arr.add(str);
}

Answer 4

for(int value=0;value<=10;value++)
{
 DBCollection tableDetails = db.getCollection("Collection Name");
 BasicDBObject queryDetails = new BasicDBObject();
 queryDetails.put("_id", value);
 DBCursor cursorDetails =tableDetails.find(queryDetails);
 DBObject oneDetails;
 boolean Name=cursorDetails.hasNext();
 while(Name)
  { 
    oneDetails=cursorDetails.next();        
    String data=oneDetails.get("HomeTown").toString();
    System.out.println(data);
  }
}