Laravel 8 多对多关系分页

Question

I have many to many relation for categories and products. In a specific category page I want to add pagination for products.

This is my code in Category model:

public function products() {
    return $this->belongsToMany(Product::class,
        'category_product',
        'category_id',
        'product_id'
    )
    ->where('is_published',1)
    ->orderBy('id','ASC')->paginate(5);
}

This is CategoryController code:

public function show($id) {       
    $category = Category::findorfail($id);        
    return view(category.show, compact('category'); 
}

This is a pagination code in category view blade:

{{ $products->links() }}

This is an error I'm getting:

App\Models\Category::products must return a relationship instance.

Any solutions?

Answer 1

The error message is pretty obvious, The relationship method must return a relationship instance. So these two are gonna work because those return an instance of type Illuminate\Database\Eloquent\Relations\BelongsToMany class:

public function products() {
    return $this->belongsToMany(Product::class,
        'category_product',
        'category_id',
        'product_id'
    );
}

// Or

public function products() {
    return $this->belongsToMany(Product::class,
        'category_product',
        'category_id',
        'product_id'
    )
    // This update the internal query of the relationship instance to query the relationship later on.
    ->where('is_published',1)->orderBy('id','ASC');
}

Your code will return an instance of Illuminate\Pagination\LengthAwarePaginator , which is NOT gonna work:

public function products() {
    return $this->belongsToMany(Product::class,
        'category_product',
        'category_id',
        'product_id'
    )
    ->where('is_published',1)
    ->orderBy('id','ASC')->paginate(5);
}

Then in your controller, you can do something like:

class CategoriesController extends Controller
{
    public function show($id)
    {
        $category = Category::findOrFail($id);
        $products = $category->products()->paginate(5);

        return view('categories.show', compact('category', '$products'));
    }
}

Answer 2

Found a solution for this:

CategoryController:

public function show($id) {       
    $category = Category::findorfail($id);
    $category->setRelation('products', $category->products()->paginate(5));
    
    return view(category.show, compact('category'); 
}

View blade:

@foreach($category->products as $product)
    {{ $product->title }}
@endforeach

{!! $category->products->render() !!}

Category model:

public function products() {
    return $this->belongsToMany(Product::class,
        'category_product',
        'category_id',
        'product_id'
    )
    ->where('is_published',1)
    ->orderBy('id','ASC');
}