Save EntityType choice as string - Symfony 4

I have entity1 and entity2.

In the entity1's form, I am displaying a choice list where the options are comming from entity2.I want to save the selected choice as string inside a column in entity1's table, but I dont want to create any relations between the tables.

How Should I do that?

class Entity1 {/** * @ORM\Column(type="string") */private $historico;}class Entity2 {/** * @ORM\Column(type="string") */private $description;}

Entity1FormType.php

$builder->add('historico', EntityType::class, ['class' => Entity2::class,'choice_label' => 'description','choice_value' => 'description','placeholder' => ''            ]);

The choices display fine, but when I submit I get the following error:

Expected argument of type "string", "App\Entity\Entity2" given.

If I use 'mapped' => false, the input submit as null.

How do I convert the entity object to string?Help a symfony noob :)