雄辩的急切加载不适用于我的命名约定

Question

I have been stuck for most of the day getting an empty array any time I eager loaded product images while requesting products in my controller in Laravel.

public function ProductImages() {
        return $this->hasMany('App\ProductImage', 'product_id'); // this matches the Eloquent model
  }

I changed my code to make the FK 'test' and suddenly it has started returning the appropriate data I want back. I put the FK back to product_id but again am back to an empty array. Below are My product Model ProductImages Model and the migrations for both with the call Im making in the controlelr

Product Model

class Product extends Model
{
 protected $fillable = array('name', 'url_name', 'sku', 'description', 'short_description', 'enabled', 'track_inventory', 'stock_level', 'allow_backorder', 'updated_user_id' );

//protected $hidden = array('id');


// LINK THIS MODEL TO OUR DATABASE TABLE ---------------------------------
// Database table is not called my_products
protected $table = 'products';

// each  product HAS many product images
public function ProductImages() {
    return $this->hasMany('App\ProductImage', 'productId'); // this matches the Eloquent model
}
}

Product Images Model

class ProductImage extends Model
{
 protected $fillable = array('name', 'description', 'path', 'sort_order', 'product_id');
// DEFINE RELATIONSHIPS --------------------------------------------------
// each attribute HAS one product
public function Product() {
    return $this->belongsTo('App\Product', 'id'); // this matches the Eloquent model
}
}

Product Migration

class CreateProductsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('products', function (Blueprint $table) {
            $table->increments('id');

            $table->string('name');
            $table->string('url');
            $table->string('sku');
            $table->string('description');
            $table->string('short_description');
            $table->integer('enabled');
            $table->integer('track_inventory');
            $table->integer('stock_level');
            $table->integer('allow_backorder');
            $table->dateTime('updated_user_id');



            $table->timestamps();
        });
    }
}

Product Images Migration

class CreateProductImagesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('product_images', function (Blueprint $table) {
            $table->increments('id');


            $table->string('name');
            $table->string('description');
            $table->string('path');
            $table->integer('sort_order');
            $table->integer('product_id')->unsigned();
            $table->foreign('product_id')->references('id')->on('products');

            $table->timestamps();
        });
    }
}

Product Controller Snippet

 public function index()
    {
        //
        $Products = Product::with('ProductImages','productTypes')->get();

        //dd($Products);

        return response()->json( $Products, 200);

    }

If you could help me understand why this strange behavior is happening i would be very grateful.