孩子不存在

Okay, this was asked, however, I tried what was given on stackoverflow. From what I understand, buildForm needs to be added. But still not working for me. I also read another answer to clear cache, that did not work either. Error is Child "someinput" does not exist.

In my EntityType:

public function buildForm(FormBuilderInterface $builder, array $options)
{

    $builder
        ->add('someinput', 'text',array('mapped'=>false))
    ;
}

Next, in my controller:

$en = new Model();
$form = $this->createFormBuilder()->getForm();
$request = $this->get('request');
$form->handleRequest($request);            
if($request->getMethod()=='POST'){
    $input_value = $form->get("someinput")->getData();
...}

View: I tried:

{{form_start(form)}}
    {{form_widget(form)}}
{{form_end(form)}}

Also tried:

<form action="" method="post">
    <input type="text" name="someinput" />
    <button type="submit">Add</button>
</form>

And tried:

{{form_start(form)}}
    {{form_row(form.someinput)}}
{{form_end(form)}} 

You must create the form first:

$form = $this->createForm(new ModelFormType());

ModelFormType is your form type class where you added someinput text field.