Look at my codes, I want to save the information, then everything falls apart.
I have three tables, houses & categories & category_house.
houses & category_house tables
    public function up()
    {
        Schema::create('houses', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->bigInteger('user_id')->unsigned();
            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
            $table->string('title');
            $table->string('slug');
            $table->string('lang');
            $table->string('image')->nullable();
            $table->text('sliders');
            $table->text('body');
            $table->timestamps();
        });
        Schema::create('category_house', function (Blueprint $table) {
            $table->bigInteger('category_id')->unsigned();
            $table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');
            $table->bigInteger('house_id')->unsigned();
            $table->foreign('house_id')->references('id')->on('houses')->onDelete('cascade');
            $table->primary(['category_id' , 'house_id']);
        });
    }
categories table
    public function up()
    {
        Schema::create('categories', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name');
            $table->string('lang');
            $table->string('href')->nullable();
            $table->integer('parent_id');
            $table->string('icon')->nullable();
            $table->timestamps();
        });
    }
edit.blade.php
    <form action="{{ route('houses.update', $house->id) }}" method="post">
        @csrf
        @method('PUT')
        <input type="hidden" name="sliders">
        <div class="col-md-6">
            <div class="form-group">
                <label for="title">Title</label>
                <input type="text" class="form-control" id="title" name="title" value="{{ old('title') ?? $house->title }}">
            </div>
        </div>
        <div class="col-md-12">
            <div class="form-group">
                <label for="body">Body</label>
                <textarea class="form-control" id="body" name="body">{{ old('body') ?? $house->body }}</textarea>
            </div>
        </div>
        <div class="col-md-6">
            <div class="form-group">
                <label for="category">Sub Category</label>
                <select name="category" id="category" class="form-control">
                    @foreach($categories as $category)
                        <option value="{{ $category->id }}" {{ $house->categories()->pluck('id')->contains($category->id) ? 'selected' : '' }}>
                            {{ $category->name }}
                        </option>
                    @endforeach
                </select>
            </div>
        </div>
        <div class="col-md-6">
            <div class="form-group">
                <label for="lang">Language</label>
                <select id="lang" name="lang" class="form-control">
                    <option value="fa" {{ $house->lang == 'fa' ? 'selected' : '' }}>Farsi</option>
                    <option value="en" {{ $house->lang == 'en' ? 'selected' : '' }}>English</option>
                </select>
            </div>
        </div>
        //.....
        <div class="form-group">
            <button class="btn btn-primary btn-lg btn-block">
                <i class="fas fa-check ml-2"></i>Save
            </button>
        </div>
    </form>
HouseController.php
     public function update(Request $request, House $house)
    {
        $house->user_id = 1;
        $house->title = $request->title;
        $house->lang = $request->lang;
        $house->body = $request->body;
        if($request->has('image')) {
            $image = $request->file('image');
            $filename = $image->getClientOriginalName();
            $image->move(public_path('images/slideShows'), $filename);
            $house->image = $request->file('image')->getClientOriginalName();
}
        $house->save();
        $house->categories()->sync($request->category);
        $category = Category::findOrFail($request->get('category'))->getParent();
        $category->name = $request->title;
        $category->parent_id = $request->category;
        $category->lang = $request->lang;
        $category->href = $request->slug;
        $category->save();
        return redirect()->route('houses.index');
    }
Category.php
    public function getParent ()
    {
        return $this->hasOne(Category::class, 'id', 'parent_id')->withDefault(['name' => '-']);
    }
For example, I have the following cateories in database.
id`----`name`-----------------`lang`------`href`---------`parent_id`--------`icon`-----------------`created_at`--------`updated_at
8`-----`Main Menu`--------`en`----------`NULL`------`0`---------------------`fas fa-cube`------`NULL`----------------`NULL
The correct method should be stored this way
id`----`name`-----------------`lang`------`href`----------------------`parent_id`--------`icon`-----------------`created_at`--------`updated_at
8`-----`Main Menu`--------`en`----------`NULL`-------------------`0`---------------------`fas fa-cube`------`NULL`----------------`NULL
20`---`Duplex House`----`en`----------`duplex-house`------`8`---------------------`NULL`---------------`NULL`----------------`NULL
But this way it is saved.
id`----`name`-----------------`lang`------`href`----------------------`parent_id`--------`icon`-----------------`created_at`--------`updated_at
8`-----`Duplex House`----`en`---------`NULL`-------------------`8`---------------------`fas fa-cube`------`NULL`----------------`NULL
20`---`Duplex House`----`en`---------`NULL`-------------------`8`---------------------`NULL`---------------`NULL`----------------`NULL
And when I changed this code 
    $category = Category::findOrFail($request->get('category'))->getParent();
I want to add slug to href.
- slug => house
- href => categories