Laravel update hasMany relationship - laravel

Question

I just read more documentation and issues for this problem to resolve that , but nothing work for me, i have 2 table wit this models:
class Month extends Model
{
protected $guarded = ['id'];
public function lessons()
{
return $this->hasMany(Lesson::class);
}
}
class Lesson extends Model
{
protected $guarded = ['id'];
public function months()
{
return $this->belongsTo(Month::class);
}
}
I can save some data with relation ship with this sample code and that work fine:
$month = Month::find(1);
$lesson = new Lesson();
$lesson->title = $request->title;
$lesson->content = $request->content;
$lesson->file_url = $uploadedFilePath;
$lesson->filename = $filename;
$lesson->time = $request->time;
$month = $month->lessons()->save($lesson);
now I try to update some lesson fields with this code:
$lesson = Lesson::find($id);
$lesson->update([
'title' => $request->title,
'content' => $request->content,
'file_url' => $uploadedFilePath,
'filename' => $filename,
'time' => $request->time
]);
$month = Month::find($request->months['0']);
$lesson = Lesson::find($lesson->id);
$lesson->months()->associate($month)->save();
in that I try to change month_id column on Lesson table in database with for example $month->id value, how can I do that?
UPDATED:
class Lesson extends Model
{
protected $guarded = ['id'];
public function month()
{
return $this->belongsTo(Month::class);
}
}
Controller:
$lesson->update([
'title' => $request->title,
'content' => $request->content,
'file_url' => $uploadedFilePath,
'filename' => $filename,
'time' => $request->time
]);
$month = Month::find($request->months['0']);
$lesson = Lesson::find($lesson->id);
$lesson->month()->associate($month)->save();
$lesson->update(['month_id' => $month->id]);
Migrations:
Schema::create('months', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->string('description');
$table->string('price');
$table->timestamps();
});
Schema::create('lessons', function (Blueprint $table) {
$table->increments('id');
$table->integer('month_id')->unsigned();
$table->string('title');
$table->longText('content');
$table->string('file_url');
$table->string('filename');
$table->string('time', 50);
$table->foreign('month_id')->references('id')->on('months')->onDelete('cascade');
$table->timestamps();
});

Answer 1

Firstly, the name of method months() should be renamed to month because it's returning single month not multiple months.
Secondly, If your Lesson has a field called month_id then its far simpler than you are thinking about. We can just change these two lines:
$lesson = Lesson::find($lesson->id);
$lesson->months()->associate($month)->save();
To the following line:
$lesson->update(['month_id' => $month->id);
It should update the month_id of your $lesson to the $month->id