将MongoDB查询转换为Java

我需要将以下mongo查询转换为java。

db.sample.find( { name:"abc" }, { _id: 0, cities: { $elemMatch: { cityName: "A" }}}); 

我尝试了很多方法，但我无法弄清楚正确的方法。

  BasicDBObject eleMatch = new BasicDBObject(); eleMatch.put("cityName","A"); BasicDBObject up = new BasicDBObject(); up.put("$elemMatch",eleMatch); BasicDBObject query = new BasicDBObject(); query.put("name","abc"); query.put("cities",up); DBCollection dbcoll = mongoTemplate.getCollection("sample"); DBObject object = dbcoll.findOne(query); 

但是此对象的结果包含id。 所以我只需要摆脱它。

Answer 1

您需要将检索到的字段作为findOne方法的第二个参数

 BasicDBObject retrievedField = new BasicDBObject(); retrievedField.put("_id",0); dbcoll.findOne(query, retrievedField); 

此外，如果您想要检索您显示的确切查询，我认为您需要将elemMatch对象附加到retrieveFields，而不是将其添加到queryObject。

 BasicDBObject eleMatch = new BasicDBObject(); eleMatch.put("cityName","A"); BasicDBObject up = new BasicDBObject(); up.put("$elemMatch",eleMatch); retrievedField.append(up); BasicDBObject query = new BasicDBObject(); query.put("name","abc"); DBCollection dbcoll = mongoTemplate.getCollection("sample"); DBObject object = dbcoll.findOne(query, retrievedField);