A set of fields for one property entity in Symfony 2 - forms

Question

My Product entity has the following structure:
private $id;
private $title;
/**
* #ManyToOne(targetEntity="Category")
* #JoinColumn(name="cat_id", referencedColumnName="id")
*/
private $category;
Category have nested structure. And each level of nesting is shown in 5 separate fields:
In class form code, I solve it in this way:
$builder
->add('cat_1', 'entity', array(
...
'query_builder' => function() { return someSelectLogic1(); }
))
->add('cat_2', 'entity', array(
...
'query_builder' => function() { return someSelectLogic2(); }
))
->add('cat_3', 'entity', array(
...
'query_builder' => function() { return someSelectLogic3(); }
))
->add('cat_4', 'entity', array(
...
'query_builder' => function() { return someSelectLogic4(); }
))
->add('cat_5', 'entity', array(
...
'query_builder' => function() { return someSelectLogic5(); }
))
Now I need to know which field is filled in the last turn and pass the value of that field in the entity property.
In all that I do not like:
complex logic to determine which field with category was filled at the end
each of these fields is not tied to the entity 'mapped' => false
1) What the right way to organize code of my form?
2) And is there a way to bring these fields into a separate class which will deal with the logic of determining which category was chosen in the end?

Answer 1

I would suggest the following:
1) Create a new custom form field type and put all those entity in there.
This process is not much different from ordinary creation of form type. Just enclose those fields in it's own buildForm() and that should do the trick. Docs.
2) Mark all those entity fields with property "property_path => false".
Clearly you wont be storing these values inside your model.
3) Add two more fields: chosen and lastOne.
Now, this might be tricky: I would either set the chosen to text type (basically, generic type) or would use entity as well. If you go for entity you would need to include all possible answers from all entity fields. As for the lastOne set it to text as it will reflect which field (by name) was selected last.
Either way, those two fields will be invisible. Don't forget to set property_path to false for lastOne field.
4) Finally, add ValueTransformer (docs) which will contain logic to "see" which field was selected last.
Now, I dealt with it only once and don't understand it just quite yet, so your best bet would be trial and error with examples from official docs, unfortunately.
What basically you should do is to, within value-transformer, read the value of field lastOne. This will give you the name of field which was selected last. Then, using that value, read the actual last value selected. Last, set that value (object, if you've went for entity type, or it's ID otherwise) to chosen field.
That should basically do the thing.
As for the JS, I don't know if you're using any framework but I will assume jQuery. You will need to set lastOne field as your selecting items in your form.
$(function(){
$('#myform').find('select').on('change', function(){
var $this = $(this);
$this.closest('form').find('#__ID_OF_YOUR_LASTONE_FIELD').val($this.attr('name'));
});
});
I'm sorry I cannot provide you with code samples for PHP right now. It's a bit late here and will do my best to further update this answer tomorrow.