如何使用 Java 驱动程序在 MongoDB 中获取嵌入式文档数组的特定值

Question

我试图从数组中的每个嵌入文档中获取所有站点名称。我尝试使用以下语法但没有用

(网站.$.site)

{
  "user" : "username",
  "sites" : [{
      "sitename" : "site.com",
      "url" : "site.com",
      }, {
      "sitename" : "site2.com",
      "url" : "site2.com",
      },{
      "sitename" : "site2.com",
      "url" : "site2.com",
   }]
}

Answer 1

Mongo-java，

        MongoClient mongoClient = new MongoClient("localhost",27017);
        MongoDatabase database = mongoClient.getDatabase("Test");

        MongoCollection<Document> collection = database.getCollection("collection");
        ArrayList<Document> doc = new ArrayList<Document>();
        doc.add(new Document().append("$unwind","$sites"));
        doc.add(new Document().append("$project",new Document().append("sitename","$sites.sitename")));
        List<Document> results =collection.aggregate(doc).into(new ArrayList<Document>());
        for(Document res: results){
            System.out.println(res.toJson());
        }

输出：

        { "_id" : { "$oid" : "58c26ce044400b08ca6ff483" }, "sitename" : "site.com" }
        { "_id" : { "$oid" : "58c26ce044400b08ca6ff483" }, "sitename" : "site2.com" }
        { "_id" : { "$oid" : "58c26ce044400b08ca6ff483" }, "sitename" : "site2.com" }