Mongodb：查询嵌套在数组中的json对象

使用位置运算符

db.test.find(    { "array.value": "value2" },    { "array.$": 1, _id : 0 })

输出量

{ "array" : [ { "name" : "test2", "value" : "value2" } ] }

使用聚合

db.test.aggregate([    { $unwind : "$array"},    { $match : {"array.value" : "value2"}},    { $project : { _id : 0, array : 1}}])

输出

{ "array" : { "name" : "test2", "value" : "value2" } }

使用Java驱动程序

    MongoClient mongoClient = new MongoClient(new ServerAddress("localhost", 27017));    DB db = mongoClient.getDB("mydb");    DBCollection collection = db.getCollection("test");    DBObject unwind = new BasicDBObject("$unwind", "$array");    DBObject match = new BasicDBObject("$match", new BasicDBObject( "array.value", "value2"));    DBObject project = new BasicDBObject("$project", new BasicDBObject( "_id", 0).append("array", 1));    List<DBObject> pipeline = Arrays.asList(unwind, match, project);    AggregationOutput output = collection.aggregate(pipeline);    Iterable<DBObject> results = output.results();    for (DBObject result : results) {        System.out.println(result.get("array"));    }

输出

{ "name" : "test2" , "value" : "value2"}