TYPO3 singleSelect required - typo3

Question

This is my TCA field configuration
'membership_type' => [
'exclude' => 0,
'label' => $ll . '/locallang_db.xlf:my_label.type',
'config' => [
'type' => 'select',
'renderType' => 'selectSingle',
'foreign_table' => 'sys_category',
'foreign_table_where' => ' AND sys_category.parent=' . $membershipTypeParent . ' AND (sys_category.sys_language_uid = 0 OR sys_category.l10n_parent = 0) ORDER BY sys_category.sorting ASC',
'items' => [
[$llg . 'fe_users.groups.unkonwn', 0]
],
],
],
I want this field to be required. I tried setting:
['config']['eval'] = 'required';
['config']['minitems'] = 1;
But none of them seem to do the job. I found also this old thread on typo3 forge which says it is not possible https://forge.typo3.org/issues/60247. I am using TYPO3 8 now.
"Eval does not exist for select fields. However, what you're missing is a field to choose a non-empty value.
I suggest you use a multi-select with two selects (similar to fe_group in pages) where you can only select one item)."
I would prefer to stay with single select instead of multi-select. Is that possible ?

Answer 1

Eval does exist for select fields, there will be something incorrect in your configuration.
Here's an example I made which works
'exampleSelectSingle' => array(
'label' =>'Select Single',
'exclude' => 0,
'config' => array(
'type' => 'select',
'renderType' => 'selectSingle',
'eval' => 'required',
'items' => array(
['Empty',''],
['Label 1','value1'],
['Label 2','value2']
)
),
'size' => 1,
'minitems' => 1
)
This renders correctly with the first (empty) option selected, which triggers the validation:
https://i.stack.imgur.com/EXbdC.png