Check if column nullable before insert? - doctrine-orm

Question

TL;DR: Can I check if a field is nullable or not during or before persisting?
I am currently trying to find a smooth way to implement an "insert entry if sufficiently complete" form.
This simplified table is an autogenerated table for the entity class "User". Phone is nullable, the rest is not nullable in the schema.
<table>
<tr data-id="25">
<td><input type="text" data-property="FirstName">Alice</td>
<td><input type="text" data-property="LastName">Smith</td>
<td><input type="text" data-property="Mail">alice#example.org</td>
<td><input type="text" data-property="Phone"></td>
</tr>
... more populated rows and at the end one empty row for new entries
<tr data-id="*">
<td><input type="text" data-property="FirstName"></td>
<td><input type="text" data-property="LastName"></td>
<td><input type="text" data-property="Mail"></td>
<td><input type="text" data-property="Phone"></td>
</tr>
</table>
I have a simple ajax call which in the event that any input field is changed, sends data-property, value and data-id to the backend. The backend decides if this is an update or insert (data-id == *) and performs the action, returning the new id if it was an insert.
Now the big question: The update fails, of course, since the backend can't create a new entity if not all nonnullable fields are filled with information.
I was therefore wondering if there is any possibility to dynamically check before any insert if a field is nullable or not.

Answer 1

Thanks to Cerad's hint I could write a function that seems to work! Feel free to modify according to your liking!
Note that the class name must be fully qualified. I use ShortName::class for my solution.
public function getNonNullableFieldNames(EntityManagerInterface $EM, string $class_name)
{
$table_name = $EM->getClassMetadata($class_name)->getTableName();
$columns = $EM->getConnection()->getSchemaManager()->listTableColumns($table_name);
$nonnullable_fields = [];
foreach($columns as $col){
if($col->getNotnull()){
$nonnullable_fields[] = $col->getName();
}
}
return $nonnullable_fields;
}
I'm not particularly proud of the foreach-loop, but a combination of array_map and array_filter became too convoluted for my taste.