Question

我正在学习MongoDB，我在进行简单查询时遇到了麻烦。我有以下文档结构：

{
"_id" : 1,
"Title" : "Title 1",
"Author" : "Author 1",
"Comments" : [ 
    {
        "Id" : "Comment1_Id",
        "User" : "User 1",
        "Content" : "Content 1"
    }, 
    {
        "Id" : "Comment2_Id",
        "User" : "User 2",
        "Content" : "Content 2"
    }, 
    {
        "Id" : "Comment3_Id",
        "User" : "User 3",
        "Content" : "Content 3"
    }, 
    {
        "Id" : "Comment4_Id",
        "User" : "User 4",
        "Content" : "Content 4"
    }, 
    {
        "Id" : "Comment5_Id",
        "User" : "User 5",
        "Content" : "Content 5"
    }
] }

我正在做一些基本的事情。我要查找特定给定用户发布的所有内容。我尝试了以下查询：

db.articles.find({
    "Comments.User" : "User 5" },
  {
    "Comments.User" : 1, "Comments.Content" : 1 
  });

我希望

{
"_id" : 1,
"Comments" : [ 
    {
        "User" : "User 5",
        "Content" : "Content 5"
    }
] }

但是我得到了

{
"_id" : 1,
"Comments" : [ 
    {
        "User" : "User 1",
        "Content" : "Content 1"
    }, 
    {
        "User" : "User 2",
        "Content" : "Content 2"
    }, 
    {
        "User" : "User 3",
        "Content" : "Content 3"
    }, 
    {
        "User" : "User 4",
        "Content" : "Content 4"
    }, 
    {
        "User" : "User 5",
        "Content" : "Content 5"
    }
] }

我错过了什么吗？谢谢你的帮助

Answer 1

Mongo的find返回与查询匹配的整个文档，它不会仅返回匹配的数组元素。

要返回匹配的元素，您需要进行聚合并使用展开运算符：https://docs.mongodb.com/manual/reference/operator/aggregation/unwind/

MongoDB数组和投影

1 个答案: