MongoDB多表联查

@Autowired
    private MongoTemplate mongoTemplate;

@RequestMapping(value = "/queryByMap.html", method = RequestMethod.GET)
    public Map<String, Object> queryByMap() {
        //定义分组字段
        String[] groupIds = new String[] {"$_id","$name","$msg","$itemList",
                "$instanceItem.elementName",
                "$instanceItem"};
        //定义查询条件
        Criteria criteria = new Criteria();
        //相当于where username = "zhangsan"
        criteria.and("name").is("name0");
        //相当于 where age not in("15","20")
        //criteria.and("age").nin("15","20");
        criteria.and("msg").is("message0");
        //in操作对应的语句
        //criteria.and("").in();
        //定义排序条件
        List<Sort.Order> orders = new ArrayList();
        orders.add(new Sort.Order(Sort.Direction.DESC, "name"));
        Sort sort = Sort.by(orders);

        //联合查询条件
        Aggregation newAggregation = Aggregation.newAggregation(
                Aggregation.lookup("UDT_TestInstanceItem","name","elementName","instanceItem"),
                //从表名，主表联接字段，从表联接字段，别名

                Aggregation.unwind("$itemList"),
                Aggregation.match(criteria),
                Aggregation.group(groupIds)
                        .last("$name").as("名称")//取值，起别名
                        .first("$instanceItem.elementName").as("父项名称")
                        .first("$instanceItem.msg").as("子项msg")
                        .first("$instanceItem.name").as("子项名称"),
                Aggregation.sort(sort),
                Aggregation.skip(0),//Long类型的参数
                Aggregation.limit(100)
        );

        //查询
        AggregationResults<BasicDBObject> aggregate = mongoTemplate.aggregate(
                newAggregation ,"UDT_TestInstance",BasicDBObject.class //A表，是查询的主表
        );
        int count = mongoTemplate.aggregate(newAggregation ,"UDT_TestInstance",BasicDBObject.class).getMappedResults().size();

        Map<String, Object> result = new HashMap<>();
        result.put("result", aggregate.getMappedResults());
        result.put("count", count);
        return result;
    }