Error: dynamodb list_append returns true but does not work

Rafal Wilinski

Answered by Rafal Wilinski

What's Causing This Error

This is not exactly an error but can likely be caused due to a programmer-introduced bug. The list_append() function accepts two parameters: the initial list and the value to append.

If you provide an empty array to append to it, the function will still execute successfully, but nothing will change in the database, which might make you feel like the function does not work.

Solution: Here's How To Resolve It

To resolve the error, carefully provide the arguments for the function as shown below:

const params = {
  TableName: 'test-table',
  UpdateExpression: 'SET users = list_append(:users, newUser)'.
  ExpressionAttributeValues: {
   // append an array, as DynamoDB will join the arrays while it saves.
   newUser: [{name: 'Jake'}]   

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