Read Documents读取文档

Prerequisites先决条件

If you have not done so already, you must complete the following prerequisites before you can read documents with a MongoDB Playground:如果您还没有这样做，您必须完成以下先决条件，然后才能使用MongoDB Playground读取文档：

• Create a connection to a MongoDB deployment.创建到MongoDB部署的连接。
• Activate the connection to the MongoDB deployment.激活到MongoDB部署的连接。
• Open a MongoDB Playground.打开一个MongoDB演练场。
• Create Documents or create documents in a collection using a different method.创建文档或使用其他方法在集合中创建文档。

Read One Document读取一个文档

To read one document, use the following syntax in your Playground:要读取一个文档，请在演练场中使用以下语法：

db.collection.findOne(
   { <query> },
   { <projection> }
)

If multiple documents satisfy the query, this method returns the first document according to the natural order which reflects the order of documents on the disk.如果多个文档满足查询，此方法将根据反映文档在磁盘上的顺序的自然顺序返回第一个文档。

To learn more about this method's parameters, see findOne() in the MongoDB Manual.要了解有关此方法参数的更多信息，请参阅MongoDB手册中的findOne()。

To run your Playground, press the Play Button at the top right of the Playground View. 要运行您的演练场，请按演练场视图右上角的“播放”按钮。MongoDB for VS Code splits your Playground and outputs the results of your Playground in the Playground Results.json pane. MongoDB for VS Code拆分您的演练场，并在Playground Results.json窗格中输出演练场的结果。If you disabled split-view, MongoDB for VS Code outputs the results of your Playground in a new tab.如果您禁用了拆分视图，MongoDB for VS Code会在一个新的选项卡中输出您的演练场的结果。

You may edit any JSON document returned from a findOne() or find() operation.您可以编辑从findOne()或find()操作返回的任何JSON文档。

1. At the top of this document, click Edit Document. 在此文档顶部，单击“编辑文档”。MongoDB for VS Code opens it as an editable EJSON document titled <database>.<collection>:"<_id>".json.MongoDB for VS Code将其作为标题为<database>.<collection>:"<_id>".json的可编辑EJSON文档打开。
2. Make any edits you require.进行所需的任何编辑。
3. Press Ctrl + S (Windows/Linux) or Cmd + S to save the edited document to the MongoDB database.按Ctrl+S（Windows/Linux）或Cmd+S将编辑后的文档保存到MongoDB数据库中。
   • If the update succeeds, MongoDB for VS Code confirms that the database has stored the change.如果更新成功，MongoDB for VS Code将确认数据库已存储更改。
   • If the update results in an error, MongoDB for VS Code displays it.如果更新导致错误，MongoDB for VS Code会显示它。

use("test");

db.sales.findOne(
  { "_id" : 1 },
  { "_id" : 0 }
);

{
  item: 'abc',
  price: 10,
  quantity: 2,
  date: 2014-03-01T08:00:00.000Z
}

Read Many Documents读取多个文档

To read many documents, use the following syntax in your Playground:要读取多个文档，请在演练场中使用以下语法：

db.collection.find(
   { <query> },
   { <projection> }
)

For a detailed description of this method's parameters, see find() in the MongoDB Manual.有关此方法参数的详细描述，请参阅MongoDB手册中的find()。

To run your Playground, press the Play Button at the top right of the Playground View. MongoDB for VS Code splits your Playground and outputs the results of your Playground in the Playground Results.json pane. 要运行您的演练场，请按演练场视图右上角的“播放”按钮。MongoDB for VS Code拆分您的演练场，并在Playground Results.json窗格中输出演练场的结果。If you disabled split-view, MongoDB for VS Code outputs the results of your Playground in a new tab.如果您禁用了拆分视图，MongoDB for VS Code会在一个新的选项卡中输出您的演练场的结果。

use("test");

db.sales.find(
  { "item" : "abc" },
  { "price" : 1 }
);

[
  {
    _id: 2,
    price: 10
  },
  {
    _id: 6,
    price: 10
  },
  {
    _id: 9,
    price: 10
  },
  {
    _id: 1,
    price: 10
  }
]