How to use updateExpression with AttributesUpdates for node.js AWS dynamodb

Question

I am using the api "updateItem" in AWS dynamodb for update the items. The main feature will be add the new item or delete one existed item. However, none of them works in the following code, the error message for the ADD is " "ValidationException: Invalid UpdateExpression: Incorrect operand type for operator or function; operator or function: list_append, operand type: S. Here is the my code:

const data = "newData";
async function updatedb(data) {
    return new Promise((resolve, reject) =>{
        var params = {
             Key: {
                "lists": {
                    S: data
                }
            },
            TableName: "old_lists_DB",
             UpdateExpression: "SET #L = list_append(:v,#L) ",
            ExpressionAttributeNames: {
              "#L": "lists",
              },
           ExpressionAttributeValues: {
            ":v": {
                S: data
              }
            }
        };
        dynamodb.updateItem(params, function(err,data) {
            if(err){
                reject(err);
            }else{
                resolve(data);
            }
        });
    });
}

The schema of the old_lists_DB is very simple, only has one attribute : lists, and the value is a set of string. For example:

{
  {"lists" : "a"},
  {"lists" : "b"},   
  {"lists" : "c"},
}

FYI no need to manually create and resolve promises. Just use return dynamodb.updateItem(params).promise(). — jarmod

Balu Vyamajala Balu Vyamajala · Accepted Answer · 2021-03-08T21:41:18

considering list can't be a partition key, you have a different partition key and list is just an attribute. So, you have a string data , that you want to append to lists of type list.

with this, I see two things,

Key: This should contain partition key information, which in this case I assumed id of type string.

list_append, we should pass a list itself. so, ExpressionAttributeValues we need to frame an array with a string.

Here is modified update code.

const data = "newData2";
const id = "1";
var params = {
  Key: {
    id: {
      S: id,
    },
  },
  TableName: "old_lists_DB",
  UpdateExpression: "SET #L = list_append(:v,#L) ",
  ExpressionAttributeNames: {
    "#L": "lists",
  },
  ExpressionAttributeValues: {
    ":v": {
      L: [{ S: data }],
    },
  },
};
dynamodb.updateItem(params, function (err, result) {
  if (err) {
    console.log("err", err);
  } else {
    console.log("result", result);
  }
});

How to use updateExpression with AttributesUpdates for node.js AWS dynamodb

1 Answers