I am getting an error when trying to access and return hasOne from the controller to the frontend

Response::setContent(): Argument #1 ($content) must be of type ?string

I am getting the above error, when trying to access and return hasOne from the controller to the front end. I have created two models Product and Images.

Product Model

<?php

namespace App\Models;

use Exception;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Product extends Model
{
    use HasFactory;
    protected $fillable = [
        'sku',
        'name',
        'price',
        'status',
        'imageId'
    ];

    public function images(){
        return $this->hasOne(Image::class,'id','imageId');
    }
}

Image Model

<?php
namespace App\Models;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Image extends Model
{
    use HasFactory;
    protected $fillable = [
        'imageName',
        'imageLink'
    ];
}

Product Controller

<?php

namespace domain\Services;

use App\Models\Product;
use App\Models\Image;
use Exception;
use PhpParser\Node\Stmt\TryCatch;

class ProductService
{
    protected $item;
    public function __construct()
    {
        $this->item = new Product();
    }
    public function all()
    {
            return $this->item->images();
    }

I am getting the error when trying to return the function images function in the Model using the all() function in the controller.

In general Laravel works best when you take advantage of its strengths. For example in your code above you have $imageId instead of $image_id and you are then forced to include the id to search for in your relationship on the Product model instead use what Laravel is expecting ie $image_id in the product table. Then in the model just use

Public function Image()
{
    return $this->hasOne(Image::class);
}

Note the function name is the same as the model name. And since you have used $image_id in the product table nothing further is required.

Also consider calling the product controller ProductController and not ProductService

In answer to your question: In the constructor of the product controller you initialise a new Product model without any reference to the database this is an empty model you then call this in the all function and ask for the images property but there is nothing in the code you have displayed which will get a product model from the database.

Instead consider something like the function below for example

Public function show(Product $product)
{
 // then call the image property on the      $product variable which Laravel will get for you 
$product->load(‘Image’);
return response()->json($product);
}

In your route add ‘show_product/{product}’ and call it with the id of the product you want.