convert array object from database to string - php

Question

I'm currently coding a blog to get experience with php.
In the edit.php I want to give the category of a post if a post has one.
This is the edit.php:
<div class="categories-heading">
<?php if (!empty($entry->c_Id)): ?>
<div class="category-heading">
<h3>Category: <?php echo e($categoryFromId); ?></h3>
</div>
<div class="category-heading">
<h3>change category</h3>
</div>
</div>
<form method="post">
<div class="categories-post-edit">
<?php foreach($categories as $cat): ?>
<div class="category-post-edit">
<input type="radio" name="category" value="<?php echo e($cat->id); ?>">
<label> <?php echo e($cat->category); ?></label>
</input>
</div>
<?php endforeach; ?>
</div>
</form>
<?php else: ?>
<div class="category-heading">
<h3>choose category</h3>
</div>
</div>
<form method="post">
<div class="categories-post-edit">
<?php foreach($categories as $cat): ?>
<div class="category-post-edit">
<input type="radio" name="category" value="<?php echo e($cat->id); ?>">
<label> <?php echo e($cat->category); ?></label>
</input>
</div>
<?php endforeach; ?>
This is the part of the function edit() in the PostsAdminController.php which is relevant for this:
if(!empty($_POST['title']) AND !empty($_POST['subheading']) AND
!empty($_POST['content'])
AND !empty($_POST['category'])) {
$entry->title = $_POST['title'];
$entry->subheading = $_POST['subheading'];
$entry->content = $_POST['content'];
$entry->c_Id = $_POST['category'];
$this->postsRepository->update($entry);
$savedSuccess = true;
}
$categoryFId = $this->categoryRepository->oneCategory($entry->c_Id);
$categoryFromId = $categoryFId['category'];
var_dump($categoryFromId);
$this->render("post/admin/edit", [
'entry' => $entry,
'savedSuccess' => $savedSuccess,
'categories' => $categories,
'categoryFromId' => $categoryFromId
]);
}
And this is the function oneCategory in the CategoryRepository.php that interacts with the database.
public function oneCategory($id)
{
$table = $this->getTableName();
$model = $this->getModelName();
$stmt = $this->pdo->prepare("SELECT `category` FROM `$table`
WHERE id = :id");
$stmt->setFetchMode(PDO::FETCH_CLASS, $model);
$oneCategory = $stmt->fetch(PDO::FETCH_CLASS);
return $oneCategory;
}
oneCategory() gives out an array no matter if I put SELECT * or SELECT category in the query, that's why I put $categoryFId['category'] into a variable after.
It works, but I think there must be a more easy or quicker way (like special functions or so), I just didn't manage to find what I search for