我想更改 return 类型的 AggregationResults

Question

我目前正在通过 Spring 引导使用 mongoTemplate，我的数据结构是：

我写了下面的代码来只获取数据库中的评论列表。

        MatchOperation matchOperation = Aggregation.match(
                Criteria.where("_id").is(new ObjectId(postId))
        );

        ProjectionOperation projectionOperation = Aggregation.project()
                .and("comments").as("comments");

        Aggregation aggregation = Aggregation.newAggregation(matchOperation, projectionOperation);
        AggregationResults<Object> result = mongoTemplate.aggregate(aggregation, PostEntity.class, Object.class);
        result.getMappedResults().forEach(System.out::println);

System.out::println内容如下

{
    _id=618b37bfb6196619dbe35abb, 
    comments=[
        {
            _id=618b65c64d04820f90565c70, 
            writer=617a2d81c4033d1358e2ffba, 
            nickname=test user, 
            createDate=Wed Nov 10 15:25:10 KST 2021, 
            content=qwer, 
            replies=[], 
            likes=[]
        }, 
        {
            _id=618b66784d04820f90565c71, 
            writer=617a2d81c4033d1358e2ffba, 
            nickname=test user2, 
            createDate=Wed Nov 10 15:28:08 KST 2021, 
            content=asdf, 
            replies=[], 
            likes=[]
        }, 
        {
            _id=618b67d54d04820f90565c72, 
            writer=617a2d81c4033d1358e2ffba, 
            nickname=test user3, 
            createDate=Wed Nov 10 15:33:57 KST 2021, 
            content=asdf, 
            replies=[], 
            likes=[]
        },
        ...
    ]
}

数据导入没问题，就是不知道怎么处理。我想创建一个CommentDto对象，把上面的输出注释列表放在List<CommentDto>里，怎么办？

Answer 1

当您运行查询映射到对象时。只需将输出对象类型更改为您的 dto:

AggregationResults<CommentDto> result = mongoTemplate.aggregate(aggregation, PostEntity.class, CommentDto.class);

Answer 2

您也可以将其作为列表检索：

Aggregation aggregation = Aggregation.newAggregation(lookUp, match1, unwindPrices, unwindTags, unwindIndex, match2, groupOperation);

List<ProductVo> list = mongotemplate.aggregate(aggregation ,"products", ProductVo.class).getMappedResults();

我想更改 return 类型的 AggregationResults

I want to change the return type of AggregationResults

aggregation

spring-boot

mongotemplate