如何在MongoDB Java中检索/查找嵌套数组的所有元素 [英] How to retrieve / find all elements of a nested array in MongoDB Java

问题描述

我正在尝试将节点"数组中的所有元素查找/加载到Java列表或Hashmap中.

I am trying to find / load all elements in the "nodes" array into a Java List or Hashmap.

我正在处理无法修改的特定JSON格式. Mongo数据库集合仅包含一个文档，该文档如下所示.我正在尝试查询节点"数组的所有元素，但无法做到这一点.

I'm dealing with a specific JSON format that I cannot modify. The Mongo DB collection contains only one document, and that document is shown below. I am trying to query all elements of the "nodes" array but can't manage to do so.

MongoCollection<Document> collection = mongoDB.getCollection(collectionName); 
BasicDBObject query = new BasicDBObject();
query.put("nodes", "");
List<Document> test2 = collection.find(query).into(new ArrayList<Document>());

Test2目前返回NULL.我知道我错了，但不知道该怎么做. 这是JSON

Test2 returns NULL at the moment. I know I'm wrong but can't figure out how to do it. And here is the JSON

{
  "_id": "12123434",
  "nodes": [
    {
      "id": "1",
      "name": "bla",
      "attributes": [
        "string1",
        "string2"
      ]
    },
    {
      "id": "2",
      "name": "blabla",
      "attributes": [
        "string1",
        "string2"
      ]
    }
  ],
  "groups": []
}

推荐答案

您只需要投影nodes并进行映射.

You just need to project nodes and map.

import static com.mongodb.client.model.Projections.*;

List<Document> nodes = (List<Document>) collection.find().projection(fields(include("nodes"), excludeId())).map(document -> document.get("nodes")).first();

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