I am working on providing content editors a functionality where;

1. They select a Keyword from a Category in `field1` of Component.
2. `field2` Category will be based on Keyword selected in `field1`.

I used custom URL for this functionality and I am using Core Service to get the Category to be put in drop-down. I am saving the selected value for `field1` in text file to be used for `field2` dropdown, due to that the application is providing unexpected results if more that one editor are editing the Components. I tried following code to make sure that at any instance only one editor access the text file:

```
window.dialogArguments.controller.getItem().getLockedById()

```

but it will not work as the Component is not yet saved and `userID` or `componentID` is not yet created.

I have exhausted all the options available with custom URL to get it working correctly so I am now looking for better option than custom URL. Any suggestions would be appreciated.