update list element in dynamodb

Question

I have a list of maps as one field of a DynamoDB table. How can I update a specific element (or, rather element field ?) Trying something like

rc = table.update_item(Key={ 'username' : user }, 
    UpdateExpression="set list[:i].field = :nd",
    ExpressionAttributeValues={
        ':i' : itemnum,
        ':nd': data,
    },
    ReturnValues="UPDATED_NEW"
);

But I am getting an error:

Invalid UpdateExpression: Syntax error; token: ":i", near: "[:i]"

Any ideas how can I reference list element with variable number. Thanks.

Answer 1

Use a literal instead:

rc = table.update_item(Key={ 'username' : user }, 
    UpdateExpression="set list[" + itemnum + "].field = :nd",
    ExpressionAttributeValues={
        ':nd': data,
    },
    ReturnValues="UPDATED_NEW"
);