Spring data mongodb实现嵌套查询，并指定返回子集内容

• mongo格式：

{
    "_id" : "1",
    "userId" : "2",
    "bookId" : "1",
    "historyList" : [ 
        {
            "_id" : "1",
            "hh" : "1"
        }, 
        {
            "_id" : "2",
            "hh" : "2"
        }, 
        {
            "_id" : "3",
            "hh" : "2"
        }
    ],
    "_class" : "com.domain.UseHistory"
}

• 正常的mongoTemplate写法

Query query = new Query();
query.addCriteria(Criteria.where("userId").is("2").and("historyList._id").is("1"));
System.out.println(query.toString());
return mongoTemplate.find(query,UseHistory.class);

 但是这种写法不能满足，会将符合查询要求的整行数据全部返回，包含所有的子集。

• Aggregation写法

  History history = null;
          //封装对象列表查询条件
          List commonOperations = new ArrayList<>();
          //1. 指定查询主文档
          MatchOperation match = Aggregation.match(Criteria.where("userId").is("2"));
          commonOperations.add(match);
          //2. 指定投影，返回哪些字段
          ProjectionOperation project = Aggregation.project("historyList");
          commonOperations.add(project);
          //3. 拆分内嵌文档
          UnwindOperation unwind = Aggregation.unwind("historyList");
          commonOperations.add(unwind);
          //4. 指定查询子文档
          MatchOperation match2 = Aggregation.match(
                  Criteria.where("historyList.hh").is("2"));
          commonOperations.add(match2);
  
          //创建管道查询对象
          Aggregation aggregation = Aggregation.newAggregation(commonOperations);
          AggregationResults reminds = mongoTemplate
                  .aggregate(aggregation, "history", JSONObject.class);
          List mappedResults = reminds.getMappedResults();
          if (mappedResults != null && mappedResults.size() > 0) {
              history = JSONObject
                      .parseObject(mappedResults.get(0).getJSONObject("historyList").toJSONString(), History.class);
          }