dynamo db error on update expression using node.js

Question

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

email

[email protected]

[email protected]

[email protected]

Then, i tried to update the table with new key "details" and its value is a list. this is my code

var AWS = require("aws-sdk");

var params =
    {
        TableName: "manaftable1",
        Key: { email: "[email protected]" },
        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));
});

But i got error like this

{
  "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
}

i need response like this after updation

column1 : email

column2 : details

[email protected] | [{"id":"1","mob":"978956"},{"id":"2","mob":"767886"}]

[email protected] |

what is the issue related with my code?

Answer 1

As AWS documentation for list_append says:

The new element must be contained in a list, for example to add 2 to a list, the operand would be [2]

So you need to append an array of objects, not just an object:

var params =
    {
        TableName: "manaftable1",
        Key: { email: "[email protected]" },
        UpdateExpression: "set #details = list_append (#details, :detailsinput)",
        ExpressionAttributeNames: {
            "#details": "details"
        },
        ExpressionAttributeValues: {
            ":detailsinput": [{ "id": "1","mob": "978956" }]
        }
    };

If the property does not exist in the object, you can use if_not_exists operand:

var params =
    {
        TableName: "manaftable1",
        Key: { email: "[email protected]" },
        UpdateExpression: "set if_not_exists(#details, []) set #details = list_append (#details, :detailsinput)",
        ExpressionAttributeNames: {
            "#details": "details"
        },
        ExpressionAttributeValues: {
            ":detailsinput": [{ "id": "1","mob": "978956" }]
        }
    };

Answer 2

Use list_append() and if_not_exists() together to append to a potentially non-existent list column:

var params = {
  TableName: "manaftable1",
  Key: { email: "[email protected]" },
  UpdateExpression: "set #details = list_append(if_not_exists(#details, :empty_list), :detailsinput)",
  ExpressionAttributeNames: {
    "#details": "details"
  },
  ExpressionAttributeValues: {
    ":detailsinput": [{ "id": "1","mob": "978956" }],
    ":empty_list": []
  }
};

Answer 3

When the details attribute is NOT present in the item, the update expression should have just SET without the list_append.

UpdateExpression : "SET #details = :details"

When the details attribute is present in the item and the new update needs to add additional elements in the list, then list_append can be used to add the new element to the list.

UpdateExpression : "set #details = list_append (#details, :details)"