Dynamic select options in form

Hi to every one, i want toknow if it’s possible to do something like that.

For Example, i’ve a a field like :

<field name="idState" title="state" field-name="state"
<drop-down allow-empty="true" current-description="">
<entity-options description="${idState}" key-field-name="idState" entity-name="TableStates">
<entity-order-by field-name="idState"/>
</entity-options>
</drop-down>
</field>

So, i can do a choice, between : {U.S.A., Europe, ...etc}

Now in the same form, i want another dinamic field where, i can choose just the Country associated to the field named ‘idState’.

<field name="idCountry" title="Country" field-name="Country"
<drop-down allow-empty="true" current-description="">
<entity-options description="${idCountry}" key-field-name="idState" entity-name="TableCountry">
<entity-order-by field-name="idCountry"/>
</entity-options>
</drop-down>
</field>

So, if i’ve choice ‘Europe’ in the field ‘idState’, i want that appear in the field ‘idCountry’ a select with : {Italy, Spain, Greece,...etc}

States, and Countries, are in two differents tables. And the countries has a reference to States table.

Thanks in advance.