Laravel 5.4 transaction and one-many relation - php

Question

I just started laravel but I'm stuck to this point and I don't find a way to do it
Basically I insert an article with a category.
With select2, I select an existing category or I create a new one.
My article model :
public function category(){
return $this->belongsTo('App\Category');
}
My categories model :
public function articles(){
return $this->hasMany('App\Article');
}
My article migration :
public function up()
{
Schema::create('articles', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->longText('content')->nullable();
$table->timestamps();
});
}
My category migration :
Schema::create('categories', function (Blueprint $table) {
$table->increments('id');
$table->string('nom')->unique();
});
Schema::table('articles', function(Blueprint $table){
$table->integer('category_id')->unsigned()->index();
});
And finally my controller function to store article (I want to use transaction) :
public function store(Request $request)
{
$this->validate($request, [
'numero' => 'required',
'category' => 'required',
'title' => 'required'
]);
$article = new Article();
DB::transaction(function() use ($request) {
$category = Category::firstOrCreate(['nom' => $request->input('category')]);
$article->title = $request->input('title');
$article->save();
});
return response()->json([
'title' => $article->title
]);
}
So I know I don't save category id into article db but my category doesn't even insert, on my debug bar I've got this :
Begin Transaction
select * from batiments where (nom = 'HI') limit 1
Rollback Transaction
And my post page give me this error :
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicata du champ '' pour la clef 'batiments_nom_unique' (SQL: insert into batiments () values ())
Someone knpw how to insert or select if exist category and insert is id into article table ?
Thank

Answer 1

$table->integer('category_id')->unsigned()->index();
You set this field as index, just remove index(). Identity field must have only unique records, but your category_id may have same value many times.

Answer 2

code:
$table->integer('categorie_id')->unsigned();
$table->foreign('categorie_id')->references('id')->on('categories');
Laravel provides support for creating foreign key constraints, which are used to force referential integrity at the database level. For example, let's define a categorie_id column on the articles table that references the id column on a categories table
laravel.com/docs/5.4/migrations#foreign-key-constraints