How i can get username? (relation db)

Controller:
getting posts

  public function actionIndex()
{
    $posts = Post::find();

    $pagination = new Pagination([
        'defaultPageSize' => 2,
        'totalCount' => $posts->count()
    ]);

    $posts = $posts->offset($pagination->offset)->limit($pagination->limit)->all();

    return $this->render(
        'index',
        [
            'posts' => $posts,
            'pagination' => $pagination
        ]
    );
}

view: showing posts texts and user id's

i can't use function getUser cause $post is not an object

and Post model:

<?php

namespace app\models;

use yii\db\ActiveRecord;

class Post extends ActiveRecord
{
/**
* @inheritdoc
*/
public static function tableName()
{
return 'post';
}

/**
 * @inheritdoc
 */
public function rules()
{
    return [
        [['user_id', 'text'], 'required'],
        [['user_id'], 'integer'],
        [['text'], 'string']
    ];
}

/**
 * @inheritdoc
 */
public function attributeLabels()
{
    return [
        'id' => 'ID',
        'user_id' => 'User ID',
        'text' => 'Text',
    ];
}

/**
 * @return \yii\db\ActiveQuery
 */
public function getUser()
{
    return $this->hasOne(User::className(), ['id' => 'user_id']);
}

}