将MongoDB查询转换成Java

Question

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，但是我找不到正确的方法。

    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);

另外，如果您想检索显示的确切查询，我认为您需要将elemMatch对象附加到retrievedFields，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);