Laravel雄辩地加入几个表

Question

I have 3 tables:

products
|id|name|about|

=categories=
|id|name|parent|

=products-categories=
|id|product_id|cat_id|

I need to take a product categories names. I have a sql query:

SELECT s.name FROM products AS p 
LEFT JOIN `products-categories` AS cats ON p.id = cats.product_id
LEFT JOIN `categories` AS s ON cats.cat_id = s.id 
WHERE product_id = 1;

And It works! But how I can do this with the help of Laravel Eloquent (Not Fluent!)

Answer 1

You can use Eloquent relationship and in this case, create two models, for both tables, ie product and Category :

class Category extends Eloquent {
    protected $table = 'categories'; // optional

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

class Product extends Eloquent {
    protected $table = 'products'; // optional

    public function categories()
    {
        return $this->belongsToMany('Category', 'products_categories', 'product_id', 'category_id');
    }
}

Now you may use these relationship methods to get related data, for example:

$product = Product::with('categories')->find(1);

This will return the product with id 1 and all the related categories in a collection so you may use $product->categories->first()->name or you may do a loop on the categories like:

foreach($product->categories as $cat) {
    echo $cat->name;
}

Also you may use join which doesn't require the relationship methods and you may use same approach to join the models that is used in Fluent (Check other answer). But either way, you need to store the category and product mappings in the products_categories table. Read more about many-to-many relationship on Laravel website .

Answer 2

Just use the leftJoin method. It works the same in Eloquent as in Query Builder.

$product = Product::leftJoin('product-categories', 'product-categories.product_id', '=', 'products.id')
->leftJoin('categories', 'categories.id', '=', 'product-categories.cat_id')
->where('product_id', 1)
->first(['categories.name']);