I have 3 tables:
region is an irre-field in country. In item i want to have an selectbox where you can choose a country and only if this country has regions there shall appear a new selectbox with the regions related to the country.
If the countries were fix i could use $TCA['item']['ctrl']['type'] = 'country';
and $TCA['item']['types']
to reload the backend and display the region selectbox if needed.
Is there any possibility in doing this with a non-fix country list checking if it has relations?
An option to hide the region-field if it has no options would solve the problem as well.
I fear this is not easily possible. You can of course create a USER element and implement the logic yourself. http://docs.typo3.org/typo3cms/TCAReference/Reference/Columns/User/Index.html
You could also play around with the "type" column property from the ctrl
section, but it sounds you already tried this.