mongodb - 在 spring data mongo 中将 ObjectId 项目到 String

Question

您好，以下是我的文档 “用户”

{
    "_id" : ObjectId("5dcab69fc6355e16d8164bd3"),
    "username" : "kellen.swift",
    "firstName" : "Kellen",
    "lastName" : "Swift",
    "authorities" : [],
    "active" : true,
    "_class" : "...User"
}

“评论”

{
    "_id" : ObjectId("5dcac8fc75de953b5c3025cb"),
    "content" : "Wonderful, thanks for the explanation",
    "videoId" : "5dcab83475de951cc80dd2f0",
    "userId" : "5dcab69fc6355e16d8164bd3",
    "active" : true,
    "_class" : "...Comment"
}

我正在使用以下查询撰写用户评论:

db.users.aggregate([
        {
            "$project": {
                "_id": {
                    "$toString": "$_id"
                },
                "username": 1,
                "firstName": 1,
                "lastName": 1,
            }
        },
        {
            $lookup: {
                    from: "comments",
                    localField: "_id",
                    foreignField: "userId",
                    as: "user_comments"
            }
        },
        {
            $unwind: "$user_comments"
        },
        {
            $project:{
                username: 1,
                name: {
                    $concat: ["$firstName", " ", "$lastName"]
                },
                content: "$user_comments.content",
                videoId: "$user_comments.videoId"
            }
        }
]);

这使用 Robo3t 给了我一个正确的结果。

当我尝试从 Spring 数据接口(interface)执行相同的命令时，我无法获得确切的结果。

以下是我的java代码:

private void getAllUserCommentsForVideo(String userId) {

        ProjectionOperation userProjections = Aggregation.project().andInclude("username", "firstName", "lastName");


        LookupOperation lookup = Aggregation.lookup(
                "comments",
                "_id",
                "userId",
                "userComments"
        );

        ProjectionOperation userCommentProject = Aggregation.project(
                "username"
        ).andInclude("userComments.content");

        Aggregation aggregation = Aggregation.newAggregation(
                userProjections,
                lookup,
                Aggregation.unwind("userComments"),
                userCommentProject
        );

        List<BasicDBObject> users = mongoTemplate.aggregate(aggregation, "users", BasicDBObject.class).getMappedResults();
        for (BasicDBObject object : users) {
            System.out.println(object.toJson());
        }

    }

从查询中，我可以看到 _id 没有正确映射，我在这里做错了什么吗？

请告诉我成功执行此操作所需的任何修改。

谢谢。

Answer 1

尝试创建自定义聚合操作以正确地将 ObjectId 映射到字符串:

AggregationOperation projectionOperation = context -> {
    Document toString = new Document("$toString", "$_id");
    Document id = new Document("_id", toString);
    Document project = new Document("$project", id);

    return project;
};