Eloquent relationship between Hospital and Unit models in Laravel is not working as expected - php

Question

I am trying to establish a one-to-many relationship between Hospital and Unit models in Laravel. A hospital can have many units, while a unit belongs to one hospital. However, the association doesn't seem to work as expected.
Here is my Hospital model:
namespace App\Models;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
class Hospital extends Model
{
use HasFactory;
protected $primaryKey = 'id';
protected $keyType = 'string';
public $incrementing = false;
public function units()
{
return $this->hasMany(Unit::class);
}
}
And here is my Unit model:
namespace App\Models;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
class Unit extends Model
{
use HasFactory;
protected $primaryKey = 'id';
protected $keyType = 'string';
public $incrementing = false;
public function hospital()
{
return $this->belongsTo(Hospital::class);
}
public function benefits()
{
return $this->belongsToMany(Benefit::class, 'benefit_unit');
}
}
Here is the code that I use to associate a hospital with a unit:
$unit = Unit::create($unitData);
$unit->hospital()->associate($hospital)->save();
manual code works for me:
$hospitalUnitData = [
'hospital_id' => $hospital->id,
'unit_id' => $unit->id,
];
DB::table('hospital_unit')->insert($hospitalUnitData);
schemas:
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
class CreateHospitalsTable extends Migration
{
public function up()
{
Schema::create('hospitals', function (Blueprint $table) {
$table->uuid('id')->primary();
$table->string('name');
$table->timestamps();
});
}
public function down()
{
Schema::dropIfExists('hospitals');
}
}
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
class CreateUnitsTable extends Migration
{
public function up()
{
Schema::create('units', function (Blueprint $table) {
$table->uuid('id')->primary();
$table->string('name');
$table->uuid('hospital_id');
$table->timestamps();
$table->foreign('hospital_id')->references('id')->on('hospitals');
});
}
public function down()
{
Schema::dropIfExists('units');
}
}
use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;
class CreateHospitalUnitTable extends Migration
{
public function up()
{
Schema::create('hospital_unit', function (Blueprint $table) {
$table->id();
$table->uuid('hospital_id');
$table->uuid('unit_id');
$table->timestamps();
$table->foreign('hospital_id')->references('id')->on('hospitals')->onDelete('cascade');
$table->foreign('unit_id')->references('id')->on('units')->onDelete('cascade');
});
}
public function down()
{
Schema::dropIfExists('hospital_unit');
}
}

Answer 1

Pivot table is only needed for many-to-many relationship.
For one-to-many relationship, all you need is a refernce ID on the model that belongs to a certain, model,
Simply think of them like this, you have hospital and unit model unit,
how do you get all units of hospital A? You simply query the Unit table with hostpal_id of hospital A (HasMany)
how do you determine what is the hospital of a unit? you get the hospital based on hostpal_id stored on that unit column (BelongsTo)
you see, you dont need an intermediate (pivot) table to connect hospital and unit.
when you call this $unit->hospital()->associate($hospital)->save(); its not updating your hospital_unit table because it updates the relationship of your Hospital and Unit relationship which is one-to-many,
which mean its just updating/adding the Hospital id to the hospital_id from the Unit table and not creating pivot entry in hospital_unit table as the relationship is not many-to-many