How to fill page field dynamically?

Hi guys,

I want to select GeneralJournalBatch.Name on a Page. After I select and validate this, I want that another field for the Journal Template Name should be filled automatically.

How can I do this?

I have tried this one in the OnValidate() of the Batch Name field name:

GeneralJournalBatch.GET(BatchNameField);
IF BatchNameField <> '' THEN
   FieldJournalTemplateName := GeneralJournalBatch."Journal Template Name";
CurrPage.UPDATE(TRUE);