How to store dropdown value in database and display selected when edit item?

I am developing custom module. Other fields are saving data in database but i have issue with Dropdown field. It's not saving value in database. My code as following:

$elements['target'] = $fieldset->addField(
        'target',
        'select',
        [
            'name' => 'target',
            'label' => __('Link Target'),
            'title' => __('Select target of slide item\'s link'),
            'required' => true,
            'options' => $model->getLinkTargetOptions()
        ]
    );

In the model file

public function getLinkTargetOptions()
{
    return [
        '_self' => __('Self'),
        '_blank' => __('Blank'),  
    ];
}   

Above code adding Dropdown in the admin form. I don't know how to store it's value.