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计算关系的总数并将其映射到结果

counting aggregate mongodb-query mongodb

0

Naman · 技术社区 · 6 年前

给予 Post 将文档键入为:

@Getter
@AllArgsConstructor
class Post {
    String publisher;
    Set<String> interests;
}

我想从一系列的帖子中找出 Set<Result> 以至于 Result 对象看起来像:

@Getter
@AllArgsConstructor
class Result {
    String interestId;
    String publisherId;
    Long count;
}

java

Set<Result> buildQuery(List<Post> postList) {
    return postList.stream()
            .flatMap(post -> post.getInterests().stream()
                    .map(interest -> new AbstractMap.SimpleEntry<>(interest, post.getPublisher())))
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
            .entrySet().stream()
            .map(e -> new Result(e.getKey().getKey(), e.getKey().getValue(), e.getValue()))
            .collect(Collectors.toSet());
}

在将其转换为mongodb查询时,这是我迄今为止所拥有的:

db.posts.aggregate([
 {"$unwind" :"$interestIds"},
 {"$group" : {"_id": {interestId: "$interestIds", publisherId:"$publisherId"}, "count": {"$sum" : 1}}},
]);

{
    "_id" : {
        "interestId" : "INTEREST1",
        "publisherId" : "PUBLISHER2"
    },
    "count" : 3.0
}

现在,我正在努力解决最后的问题 map 将其表述为预期结果的操作,即:

{
    "_id" : ...
    "interestId" : "INTEREST1",
    "publisherId" : "PUBLISHER2"
    "count" : 3.0
}

0 回复 | 直到 6 年前

1

mickl 6 年前

$project

db.posts.aggregate([
    {"$unwind" :"$interestIds"},
    {"$group" : {"_id": {interestId: "$interestIds", publisherId:"$publisherId"}, "count": {"$sum" : 1}}},
    {"$project":{ _id: 0, interestId: "$_id.interestId", publisherId: "$_id.publisherId", count: 1 }}
]);