Session.withTransaction() (mongosh method方法)

Definition定义

Session.withTransaction( <function> [, <options> ] )

New in mongosh v1.1.0mongosh v1.1.0中的新功能

Runs a specified lambda function within a transaction. If there is an error, the method retries the:在事务中运行指定的lambda函数。如果出现错误，该方法将重试：

• commit operation, if there is a failure to commit.如果提交失败，则执行提交操作。
• entire transaction, if the error permits.如果错误允许，则执行整个事务。

The Session.withTransaction() method accepts the transaction options.Session.withTransaction()方法接受事务选项。

Returns:返回	The value produced by the callback function.回调函数产生的值。

Important

mongosh Method方法

This page documents a mongosh method. This is not the documentation for database commands or language-specific drivers, such as Node.js.本页记录了一种mongosh方法。这不是数据库命令或特定语言驱动程序（如Node.js）的文档。

For the database command, see the commitTransaction command.有关数据库命令，请参阅commitTransaction命令。

For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.有关MongoDB API驱动程序，请参阅特定语言的MongoDB驱动程序文档。

Compatibility兼容性

This method is available in deployments hosted in the following environments:此方法在以下环境中托管的部署中可用：

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud：云中MongoDB部署的完全托管服务

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB：MongoDB的基于订阅的自我管理版本
• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB：MongoDB的源代码可用、免费使用和自我管理版本

Behavior行为

The Node.js driver has a version of Session.withTransaction() that is known as the Callback API. Node.js驱动程序有一个版本的Session.withTransaction()，称为回调API。The Callback API also accepts an callback, however the return type for the Node.js method must be a Promise. The mongosh Session.withTransaction() method does not require a Promise. Example -------回调API也接受回调，但是Node.js方法的返回类型必须是Promise。mongosh Session.withTransaction()方法不需要Promise。示例-------

The following example creates the balances collection and uses a transaction to transfer money between two customers.以下示例创建balances（余额）集合，并使用事务在两个客户之间转账。

Create the balances collection:创建balances（余额）集合：

use accounts
db.balances.insertMany( [
  { customer: "Pat", balance: Decimal128( "35.88" ) },
  { customer: "Sasha", balance: Decimal128( "5.23" ) }
] )

Initialize some variables that are used in the transaction:初始化事务中使用的一些变量：

var fromAccount = "Pat"
var toAccount = "Sasha"
var transferAmount = 1

var dbName = "accounts"
var collectionName = "balances"

Start a session, then run a transaction to update the accounts:启动会话，然后运行事务以更新帐户：

var session = db.getMongo().startSession( { readPreference: { mode: "primary" } } );
session.withTransaction( async() => {

   const sessionCollection = session.getDatabase(dbName).getCollection(collectionName);

   // Check needed values
   var checkFromAccount = sessionCollection.findOne(
      {
         "customer": fromAccount,
         "balance": { $gte: transferAmount }
      }
   )
   if( checkFromAccount === null ){
      throw new Error( "Problem with sender account" )
   }

   var checkToAccount = sessionCollection.findOne(
      { "customer": toAccount }
   )
   if( checkToAccount === null ){
      throw new Error( "Problem with receiver account" )
   }

   // Transfer the funds
   sessionCollection.updateOne(
      { "customer": toAccount },
      { $inc: { "balance": transferAmount } }
   )
   sessionCollection.updateOne(
      { "customer": fromAccount },
      { $inc: { "balance": -1 * transferAmount } }
   )

 } )

The lambda function includes initial checks to validate the operation before updating the balances collection.lambda函数包括在更新balances集合之前验证操作的初始检查。

MongoDB automatically completes the transaction.MongoDB自动完成事务。

• If both updateOne() operations succeed, Session.withTransaction() commits the transaction when the callback returns.如果两个updateOne()操作都成功，Session.withTransaction()将在回调返回时提交事务。
• If an exception is thrown inside the callback, Session.withTransaction() ends the transaction and rolls back any uncommitted changes.如果在回调中抛出异常，Session.withTransaction()将结束事务并回滚任何未提交的更改。