How can I set the default value Laravel <select> element? - laravel-5.8

Question

I want to retrieve database values in category name and i want to show default value in selection. This is my controller for my edit view.
I have a category_product table.
<div class="col-md-4">
<div class="form-group">
<label for="category">category</label>
<select class="form-control" name="category" id="category">
#foreach($categories as $category)
<option value="{{ $category->id }}" {{ $product->categories()->category_id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
#endforeach
</select>
</div>
</div>
ProductController.php
public function edit(Product $product)
{
$categories = Category::all();
return view('Admin.products.edit', compact('product', 'categories'));
}
Product.php
public function categories()
{
return $this->belongsToMany(Category::class);
}
I get this error.
Undefined property: Illuminate\Database\Eloquent\Relations\BelongsToMany::$category_id

Answer 1

You need to add default value in the select tag above foreach() loop.
<div class="col-md-4">
<div class="form-group">
<label for="category">category</label>
<select class="form-control" name="category" id="category">
<option value="xyz">xyz</option> /* set default option value */
#foreach($categories as $category)
<option value="{{ $category->id }}" {{$category->id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
#endforeach
</select>
</div>
</div>
If you want set category name selected then you need to match category in product collection. ( if you have catetory_id in product table )
<select class="form-control" name="category" id="category">
#foreach($categories as $category)
<option value="{{ $category->id }}" {{$product->catetory_id == $category->id ? 'selected' : '' }}>{{ $category->name }}</option>
#endforeach
</select>