查找当前的模型ID（有很多关系）

I have a laravel app that allows users to add reviews to a book.

My Routes are:

Route::get('/books/{book}/addreview', 'ReviewController@create'); 
Route::post('books/{book}/review', 'ReviewController@store');

My Review controller looks like:

public function create(Book $book) {
    return view('/reviews/create');
}

public function store(Book $book){
     $this->validate(request(),[
        'title' => 'required',
        'body' => 'required'
     ]);

     Review::create([
        'title'=>request('title'),
        'body'=>request('body'),
        'user_id'=>auth()->id(),
        'book_id'=>$book->id
     ]);
    // return redirect('/books');

}

However, I get 'Undefined variable: book' - So I'm not finding the current Book ID. How could I find the current Book ID and pass it to the view?

In Review Controller:

public function create(Book $book) {
    return view('reviews.create', compact('book'));
}

In View:

{{ $book->id }}

You have to send data to view.

public function create(Book $book) {
    return view('reviews.create', ['book' => $book]);
}

You're not passing anything to the view, you need to explicitly pass data to it so that it can be used:

return view('reviews.create', ['book' => $book]);

Then in your view, to access the book's ID you can use $book->id:

Book ID is {{ $book->id }}.

// here I add some custom name to this route which will help to generate
// a corresponding URL in the view by passing this name
// route('routename')

Route::get('/books/{book}/addreview', 'ReviewController@create')->name('review.create'); 
Route::post('/books/{book}/review', 'ReviewController@store')->name('review.store');

In your controller which render the review.create view you must pass the $book that correspond to current model binding in your route like this

public function create(Book $book){
    return View::make('reviews.create', ['book' => $book]);
}

and in the corresponding view when you create your form you must specify the action attribute like this

<form action={{ route('review.store', $book)}} method="post">
    {{ csrf_field}}

You should add public function store(Request $book) instead public function store(Book $book)

As you didn't share your Book request file.