Laravel Eloquent 表关系查询

Question

I have three mysql tables :

• students (constrained with USER_ID )
• student_in_tournament (constrained with STUDENT_ID and TOURNAMENT_ID )
• tournaments

I need an eloquent query who take ALL students by specified USER_ID and if these students are in the student_in_tournament table, it needs to join with the tournament table.

If these students are not in the student_in_tournament , they don't need to join something.

At the end, I need ALL students from one specific USER_ID , with the tournament joined if he exists in the student_in_tournament table...

I tried a inner join, but it don't give me ALL the students, only these who are in the student_in_tournament table. I also tried Student::with('studentInTournament.tournaments') but it gives me 'null' in the tournaments

Thanks

Answer 1

Try creating a M:N relation between your Student and Tournament models. Since your table and column names do not conform to what Eloquent expects, you'll need to pass all 4 parameters when creating the relationship.

https://laravel.com/docs/8.x/eloquent-relationships#many-to-many-model-structure

// Student model
public function tournaments()
{
    return $this->belongsToMany(Tournament::class, 'student_in_tournament', 'STUDENT_ID', 'TOURNAMENT_ID');
}

https://laravel.com/docs/8.x/eloquent-relationships#many-to-many-defining-the-inverse-of-the-relationship

// Tournament model
public function students()
{
    return $this->belongsToMany(Student::class, 'student_in_tournament', 'TOURNAMENT_ID', 'STUDENT_ID');
}

$students = Student::query()
    ->where('USER_ID', $user_id) // or whereIn('USER_ID', $user_ids) if you have multiple user ids
    ->with('tournaments')
    ->get();    

https://laravel.com/docs/8.x/blade#loops

@foreach($students as $student)
  <!-- show student information -->
  @forelse($student->tournaments as $tournament)
    <!-- show tournament information -->
  @empty
    <!-- student has no tournaments -->
  @endforelse
  <hr>
@endforeach