AWS SDK JavaScript v3 / 如何在 dynamoDB 扫描命令中使用 ExpressionAttributeNames？

Question

我正在使用 Lambda 函数，该函数从 dynamoDB table 中的用户 ID 获取用户电子邮件。我使用 dynamoDB 扫描命令扫描 dynamoDB table 中的所有项目。我使用新的 v3 AWS JS SDK。

问题：为什么 ExpressionAttributeNames 在我的情况下不能正常工作？

这个有效：

const params = {    
  FilterExpression: "user_info.user_id = :userid",  
  ExpressionAttributeValues: {
   ":userid": { S: user_id }
  },
  ProjectionExpression: "user_email",
  TableName: aws_table,
}

但这不起作用，为什么？

const params = {
  FilterExpression: "#xyz = :userid",  
  ExpressionAttributeNames: {
    "#xyz": "user_info.user_id"  // <- filter does not work like this (returns 0 findings)
  },
  ExpressionAttributeValues: {
    ":userid": { S: user_id }
  },
  ProjectionExpression: "user_email",
  TableName: aws_table,
};

---

我的 Lambda 扫描操作代码本身如下所示：

const  { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const  { ScanCommand } = require("@aws-sdk/client-dynamodb");
const ddbClient = new DynamoDBClient({ region: aws_region });
...  

const run = async () => {
  try {
    const data = await ddbClient.send(new ScanCommand(params));
    data.Items.forEach(function (element, index, array) {
      console.log(element);
    });
    return data;
  } catch (err) {
    console.log("Error", err);
  }
}

await run();

---

npm i @aws-sdk/client-dynamodb

---

文档：

https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/clients/client-dynamodb/interfaces/scancommandinput.html#expressionattributenames

Answer 1

这是expected behaviour:

DynamoDB interprets a dot in an expression attribute name as a character within an attribute's name

// use multiple expression attribute names if you need a dynamic path:
FilterExpression: "#user_info.#user_id = :userid"