title: dynamo db error on update expression using node.js
body: <p>i need to update a list on my aws-dynamo database. i have created a table with partition key : email. then iam insert some email id to the table successfully. Now my table like this</p>
  
  <h2>email</h2>
  
  <p>manaf1@gmail.com</p>
  
  <p>manaf2@gmail.com</p>
  
  <p>manaf3@gmail.com</p>
  
  <p>Then, i tried to update the table with new key "details" and its value is a list. this is my code</p>
  
  <pre><code>var AWS = require("aws-sdk");
  
  var params =
      {
          TableName: "manaftable1",
          Key: { email: "manaf1@gmail.com" },
          UpdateExpression: "set #details = list_append (#details, :detailsinput)",
          ExpressionAttributeNames: {
              "#details": "details"
          },
          ExpressionAttributeValues: {
              ":detailsinput":{ "id": "1","mob": "978956" }
          }
      };
  
  
  var docClient = new AWS.DynamoDB.DocumentClient();
  
  docClient.update(params, function (err, data) {
      if (err)
          console.log(JSON.stringify(err, null, 2));
      else
          console.log(JSON.stringify(data, null, 2));
  });
  </code></pre>
  
  <p>But i got error like this</p>
  
  <pre><code>{
    "message": "Invalid UpdateExpression: Incorrect operand type for operator or function; operator or function: list_append, operand type: M",
    "code": "ValidationException",
    "time": "2016-10-26T11:04:60.756",
    "requestId": "SN0NPRHDFHUKBBJHOVI0DFHHRQNSO5AEMVJFFGHF9ASFHUAAJG",
    "statusCode": 400,
    "retryable": false,
    "retryDelay": 0
  }
  </code></pre>
  
  <p>i need response like this after updation</p>
  
  <p>column1 : email</p>
  
  <p>column2 : details</p>
  
  <blockquote>
    <p>manaf1@gmail.com |
    [{"id":"1","mob":"978956"},{"id":"2","mob":"767886"}]</p>
    
    <p>manaf2@gmail.com |</p>
  </blockquote>
  
  <p>what is the issue related with my code?</p>