Use the Convenient Transaction API使用便捷事务API

Sample Data样品数据

The inventory collection contains the following documents:inventory集合包含以下文档：

{ item: "sunblock", qty: 85, price: 6.0 },
{ item: "beach chair", qty: 30, price: 25.0 }

You store purchase records in the orders collection of the testdb database. This collection is empty, as there have been no purchases.您将购买记录存储在testdb数据库的orders集合中。此集合是空的，因为没有购买。

Implementation实施

The code example in this section demonstrates how to use the Convenient Transaction API to perform a multi-document transaction in a session. In this example, the transaction makes the changes needed when a customer purchases items from your shop.本节中的代码示例演示了如何使用方便事务API在会话中执行多文档事务。在这个例子中，当客户从你的商店购买商品时，事务会进行所需的更改。

This example code performs a transaction through the following actions:此示例代码通过以下操作执行事务：

1. Calls the withSession() method on the client to implicitly create the session and run the callback passed to it within the session.在客户端调用withSession()方法隐式创建会话，并在会话中运行传递给它的回调。
2. Calls the withTransaction() method on the session to create a transaction, run the callback passed to it, and commit the transaction. If the transaction fails, this method ends the transaction and returns an error message.在会话上调用withTransaction()方法以创建事务，运行传递给它的回调，并提交事务。如果事务失败，此方法将结束事务并返回错误消息。

3. Performs the following operations within the transaction:在事务中执行以下操作：

   • Updates the inventory and orders collections if there is sufficient inventory to fulfill the purchase如果有足够的库存来完成采购，则更新inventory和orders集合
   • Ends the transaction and throws an exception if there isn't sufficient inventory for any item in the order如果订单中的任何商品没有足够的inventory，则结束事务并抛出异常
   • Returns a message acknowledging that the transaction committed successfully with a copy of the purchase record返回一条消息，确认事务已成功提交，并附上购买记录的副本
4. Prints the return type of withSession(), which is either the error message or the acknowledgment that the transaction completed.打印withSession()的返回类型，它要么是错误消息，要么是事务完成的确认。

const txnResult = await client.withSession(async (session) =>
  session
    .withTransaction(async (session) => {
      const invColl = client.db("testdb").collection("inventory");
      const recColl = client.db("testdb").collection("orders");

      let total = 0;
      for (const item of order) {
        /* Update the inventory for the purchased items. End the transaction if the quantity of an item in the inventory is insufficient to complete the purchase.更新采购物品的inventory。如果inventory中某个项目的数量不足以完成采购，则结束事务。 */
        const inStock = await invColl.findOneAndUpdate(
          {
            item: item.item,
            qty: { $gte: item.qty },
          },
          { $inc: { qty: -item.qty } },
          { session }
        );
        if (inStock === null) {
          await session.abortTransaction();
          return "Item not found or insufficient quantity.";
        }
        const subTotal = item.qty * inStock.price;
        total = total + subTotal;
      }

      // Create a record of the purchase创建购买记录
      const receipt = {
        date: new Date(),
        items: order,
        total: total,
      };
      await recColl.insertOne(receipt, { session });
      return (
        "Order successfully completed and recorded!\nReceipt:\n" +
        JSON.stringify(receipt, null, 1)
      );
    }, null)
    .finally(async () => await client.close())
);

console.log(txnResult);

Sample Orders and Transaction Results订单和事务结果示例

This section describes the results of the transactions performed for two sample orders.本节描述了对两个示例订单执行的事务结果。

Sufficient inventory exists for the following order, so the transaction successfully completes:以下订单有足够的inventory，因此事务成功完成：

{ item: "sunblock", qty: 3 },
{ item: "beach chair", qty: 1 }

After passing this order to the example transaction code, the code outputs the following result:将此订单传递给示例事务代码后，代码输出以下结果：

Order successfully completed and recorded!
Receipt:
{
  "date": "2023-08-25T20:06:52.564Z",
  "items": [
    { "item": "sunblock", "qty": 3 },
    { "item": "beach chair", "qty": 1 }
  ],
  "total": 43,
  "_id": "..."
}

In the inventory collection, the quantity of "sunblock" is now 82 and the quantity of "beach chair" is 29. The orders collection contains the record of the purchase.在inventory集合中，"sunblock"（防晒霜）的数量现在是82，"beach chair"（沙滩椅）的数量是29。orders集合包含采购记录。

There is not sufficient inventory for the following order, so the driver ends the transaction:以下订单没有足够的inventory，因此司机结束事务：

{ item: "volleyball", qty: 1 }

After passing this order to the example transaction code, the code outputs the following result:将此订单传递给示例事务代码后，代码输出以下结果：

Item not found or insufficient quantity.

Since the driver ends the transaction, there are no changes to the inventory and orders collections.由于驱动程序结束了事务，inventory和orders集合没有变化。