如果关系已存在，则Laravel save（）

I'm currently using the save() feature (doc) so save a child item to a parent. But the case where the child is already attached to the parent is not handled.

So I have created this:

//Validation stuff

$parent = Task::find( request('parent') );
$child = Task::find( request('child') );

if ( \DB::table('task_has_predecessors')
            ->where('child_id', request('child'))
            ->where('parent_id' , request('parent'))
            ->count() == 0 )
{
    if ( $parent->childs()->save($child) ) 
    {
        flash('Link saved.');
    } 
    else 
    {
        flash()->error('Unable to create the link.');
    } 
}
else
{
    flash()->warning('This link already exist.');
}

But I'm not a big fan of this solution... Is there a better way to achieve this without using if ( \DB::table('...')->where(...)->where(...)->count() == 0 )?

Has laravel a magic way to manage this kind of behaviour?

I don't have any model related to the tasks_has_predecessors table. And my relationships are made like this:

class Task extends Model
{
    public function childs()
    {
        return $this->belongsToMany(ChecklistCategoryTask::class, 'task_has_predecessors',  'parent_id','child_id');
    }

    public function parents()
    {
        return $this->belongsToMany(ChecklistCategoryTask::class, 'task_has_predecessors' , 'child_id' , 'parent_id');
    }
}

If you're trying to attach one model to another, use the attach() method instead of save and ID instead of an object:

$parent->childs()->attach($child->id);

And if you're trying to create a new object, use findOrNew() instead of find():

$child = Task::findOrNew(request('child'));

This method will create a new object if it doesn't exist yet.

See Belongs To Relationships

From doc

$account = App\Account::find(10);
$user->account()->associate($account);
$user->save();