How to add/update DynamoDB entries, creating or appending to a list attribute?

Question

Here's my use case, I need to add and update entries in a DynamoDB table like this:

If the partition key doesn't exist, add it and add a new one element list containing a string value. If the partition key does exist, add a new string to its list attribute. I have code that Python/boto3 looks like this:

response = ddb_client.update_item(
    TableName=target_ddb_table,
    Key={'email-hash': {'S' : encrypted_hashed_pw},},
    ExpressionAttributeValues={ ":my_value":[{"S":"test"}], ":empty_list":[] },
    UpdateExpression='SET site_ids = list_append(if_not_exists(site_ids, :empty_list), :my_value)',
    ReturnValues='ALL_NEW'
)

I'm getting these errors, I realize that I'm doing something dumb here:re

Invalid type for parameter ExpressionAttributeValues.:empty_list, value: [], type: <class 'list'>, valid types: <class 'dict'>
Invalid type for parameter ExpressionAttributeValues.:my_value, value: [{'S': 'test'}], type: <class 'list'>, valid types: <class 'dict'>

matthewcummings516 · Accepted Answer · 2018-04-29 23:52:26Z

2

Figured it out, I need to add the type info for the Lists:

":my_value": {"L": [{"S": "test"}]}, ":empty_list": {"L": []}

answered Apr 29, 2018 at 23:52

matthewcummings516

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