mongodb 聚合函数-ProjectionOperation

 ProjectionOperation projection = Aggregation.project()
                .and(ConditionalOperators.when(Criteria.where("flag").is(true)).then("是").otherwise(
                        ConditionalOperators.when(Criteria.where("flag").is(false)).then("否").otherwise("未标记")
                )).as("flag");

        Aggregation aggregation = Aggregation.newAggregation(projection);

        List<JSONObject> result = mongoTemplate.aggregate(aggregation, "test1", JSONObject.class).getMappedResults();
        for (JSONObject demo : result) {
            System.out.println("demo = " + demo);
        }