Laravel关联关系，如果不存在则创建

Question

嗨，我是新来的拉威尔，在理解如何建立人际关系方面有点挣扎。我试图在laravel中创建一个基本的restful api，有3个模型

class Book extends Model {
   public function author()
   {
        return $this->belongsTo(Author::class);
   }

   public function categories()
   {
        return $this->belongsToMany('App\Category', 'category_book')
        ->withTimestamps();
   }

}

class Author extends Model
{
    public function books(){
        return $this->hasMany(Book::class);
    }
}

class Category extends Model
{
    public function books()
    {
        return $this->belongsToMany('App\Book', 'category_book')
           ->withTimestamps();
    }
}

表迁移：

Schema::create('books', function (Blueprint $table) {
    $table->engine = "InnoDB";
    $table->increments('id');
    $table->string('ISBN', 32);
    $table->string('title');
    $table->integer('author_id')->unsigned();
    $table->float('price')->default(0);
    $table->timestamps();
});

Schema::create('authors', function (Blueprint $table) {
    $table->engine = "InnoDB";
    $table->bigIncrements('id');
    $table->string('name');
    $table->string('surname');
    $table->timestamps();
});

  Schema::create('categories', function (Blueprint $table) {
    $table->engine = "InnoDB";
    $table->bigIncrements('id');
    $table->string('name');
    $table->timestamps();
}); 

Schema::create('category_book', function (Blueprint $table) {
    $table->bigIncrements('id');
    $table->integer('category_id')->unsigned();
    //$table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');
    $table->integer('book_id')->unsigned();
    //$table->foreign('book_id')->references('id')->on('books')->onDelete('cascade');
    $table->timestamps();
});   

书籍是主要的表格，作者与书籍有一对多的关系。类别与书籍有多对多的关系，因为一本书可以在多个类别中。

books表有一个author_id字段将其链接到author表。还有一个名为category_books的透视表，它包含category_id和book_id，用于将书籍链接到类别。

假设我想创建一个新的图书记录，如果作者存在，则将图书与该作者关联；如果不存在，则我想创建一个新的作者记录，然后将图书与该作者关联？

我也希望能够做同样的事情与类别

我的BookController中有以下内容：

    public function store(Request $request)
    {
        $book = new book;
        $book->title = $request->title;
        $book->ISBN = $request->ISBN;
        $book->price = $request->price;
        $book->categories()->associate($request->category);
        $book->save();

        return response()->json($book, 201);
    }

Answer 1

首先，排队

$book->categories()->associate($request->category);

当要更新属性To关系时，将使用方法Associates（）。

其次，如果要关联可能存在或不存在的作者，可以使用first或create方法。

$author = Author::firstOrCreate([
    'name' => $request->author_name,
    'surname' => $request->author_surname
]);
$book->author()->associate($author);

你也可以对分类或书籍做同样的处理。

$category = Category::firstOrCreate([
    'name' => $request->category_name
]);
$book->categories()->attach($category);

$book = Book::firstOrCreate([
    'ISBN' => $request->book_isbn,
    'title' => $request->book_title,
    'price' => $request->book_price
]);
$category->books()->attach($book);

firstOrCreate（）的使用在这里有文档记录https://laravel.com/docs/5.8/eloquent#other-创建方法本页有更多关于雄辩的关系方法https://laravel.com/docs/5.8/eloquent-relationships