Add a string to a list in a dynamodb table - node.js

Question

So I have been working with dynamodb in a nodejs express app and I have a specific table that has a field which is just empty lists and I want to append a string to the list.
The table name is "dev_entrants" and here is an example of the table:
----------------------------------------
primary Key Sort Key
eventID | eventType | entrants
----------------------------------------
Qual-919-w5wm1xhnw | Qual | []
----------------------------------------
So I receive a post request and then route it through express and it comes to a function where after doing type checks and all that I try to add stuff to my table with:
import AWS from 'aws-sdk';
const docClient = new AWS.DynamoDB.DocumentClient({region: 'us-west-1'});
const db = {
docClient
};
...
const entrantsParams = {
'TableName' : 'dev_entrants',
'Key': {
'eventID' : 'Qual-919-w5wm1xhnw',
},
'UpdateExpression' : "SET #attrName = list_append(#attrName, :attrValue)",
'ExpressionAttributeNames' : {
'#attrName' : 'entrants'
},
'ExpressionAttributeValues' : {
':attrValue' : ['joe'],
}
};
const updateEntrantsPromise = db.docClient.update(entrantsParams).promise();
(For the purpose of this example I have replaced variables with the strings they represent)
I have spent 6 hours or so reading through different documentation, as well as on stack overflow trying to find the answer.
The current error i get is the provided key element does not match the schema. If I remove the brackets around the attrValue then I get wrong operand type. I know the key exists in the table as i copied and pasted it from there. Also I am succesfully adding things to the table from another function so my connection is working fine. Can anyone please help me out?

Answer 1

You need to include the eventType in the Key object because your table schema has a sort key. If your table has a sort/partition key then you need to include it along with the primary key. Try it with the following:
const entrantsParams = {
'TableName' : 'dev_entrants',
'Key': {
'eventID' : 'Qual-919-w5wm1xhnw',
'eventType' : 'Qual'
},
'UpdateExpression' : "SET #attrName = list_append(if_not_exists(#attrName, :empty_list), :attrValue)",
'ExpressionAttributeNames' : {
'#attrName' : 'entrants'
},
'ExpressionAttributeValues' : {
':attrValue' : ['joe'],
':empty_list': []
}
};