查询以获取 MongoDB 中特定键的值

Question

我有一个 collection，其中包含以下格式的记录。

{
"_id" : 21,
"title" : "3D User Interfaces with Java 3D",
"isbn" : "1884777902",
"pageCount" : 520,
"publishedDate" : ISODate("2000-08-01T07:00:00Z"),
"thumbnailUrl" : "https://s3.amazonaws.com/AKIAJC5RLADLUMVRPFDQ.book-thumb-images/barrilleaux.jpg",
"longDescription" : "3D User Interfaces with Java 3D is a practical guide for providing next-generation applications with 3D user interfaces for manipulation of in-scene objects. Emphasis is on standalone and web-based business applications, such as for online sales and mass customization, but much of what this book offers has broad applicability to 3D user interfaces in other pursuits such as scientific visualization and gaming.  This book provides an extensive conceptual framework for 3D user interface techniques, and an in-depth introduction to user interface support in the Java 3D API, including such topics as picking, collision, and drag-and-drop. Many of the techniques are demonstrated in a Java 3D software framework included with the book, which also provides developers with many general-purpose building blocks for constructing their own user interfaces.    Applications and their use of 3D are approached realistically. The book is geared towards sophisticated user interfaces for the \"everyday user\" who doesn't have a lot of time to learn another application--much less a complicated one--and an everyday computer system without exotic devices like head mounted displays and data gloves. Perhaps the best description of this book is: \"A roadmap from Java 3D to 'Swing 3D'.\"",
"status" : "PUBLISH",
"authors" : [
    "Jon Barrilleaux"
],
"categories" : [
    "Java",
    "Computer Graphics"
]

}

我想要做的是从 collection.

中提取所有标题值

我尝试使用类似的东西：

db.<Collection_name>.find(title)

但它 returns 一个错误 ReferenceError: title is not defined.

能否请您提供您的建议来完成这项工作。

Answer 1

.find() 方法有两个参数：第一个用于查询（你可以传递一个空对象），第二个定义一个投影（应该返回哪些字段）所以你的查询应该是这样的：

db.<Collection_name>.find({}, { title: 1 })

查询以获取 MongoDB 中特定键的值

Query to get values for particular key in MongoDB

collections

mongodb

nosql

mongoid

mongodb-query