HasMany relationship doesn't work in Laravel

Question

I have registration form generated through php artisan make:auth command in Laravel project. I want to customize it a bit by adding functionality that user can select his/her gender when registering. I made genders table that has genders column with two values Man and Woman and also added gender_id column in users table. I hasMany relationship but when I try and register user he is registered but gender_id columns is still NULL. I don't know where the mistake is. Any help is appreciated. Here is my code.

RegisterController.php

<?php

namespace App\Http\Controllers\Auth;

use App\Gender;
use App\User;
use App\Http\Controllers\Controller;
use Illuminate\Support\Facades\Hash;
use Illuminate\Support\Facades\Validator;
use Illuminate\Foundation\Auth\RegistersUsers;

class RegisterController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Register Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles the registration of new users as well as their
    | validation and creation. By default this controller uses a trait to
    | provide this functionality without requiring any additional code.
    |
    */

    use RegistersUsers;

    protected $redirectTo = '/home';


    public function __construct()
    {
        $this->middleware('guest');
    }

    protected function validator(array $data)
    {
        return Validator::make($data, [
            'genders' => ['required', 'string', 'max:255'],
            /* 'gender_id' => 'required|exists:mysql.genders,id', */
            'name' => ['required', 'string', 'max:255'],
            'email' => ['required', 'string', 'email', 'max:255', 'unique:users'],
            'age' => ['required', 'integer', 'min:18'],
            'password' => ['required', 'string', 'min:8', 'confirmed'],
        ]);
    }

    protected function create(array $data)
    {
        $genders = Gender::where('genders', request()->genders)->get()->pluck('id')->first();

        $user = User::create([
            'genders_id' => $genders,
            'name' => $data['name'],
            'email' => $data['email'],
            'age' => $data['age'],
            'password' => Hash::make($data['password']),
        ]);

        return $user;
    }
}

register.blade.php

@extends('layouts.app')

@section('content')
<div class="container">
    <div class="row justify-content-center">
        <div class="col-md-8">
            <div class="card">
                <div class="card-header">{{ __('Register') }}</div>

                <div class="card-body">
                    <form method="POST" action="{{ route('register') }}">
                        @csrf




                        <div class="form-group row">
                            <label for="genders" class="col-md-4 col-form-label text-md-right">{{ __('Genders') }}</label>
                            <div class="col-md-6">


 <select id="genders" class="form-control @error('genders') is-invalid @enderror" name="genders" value="{{ old('genders') }}" required autocomplete="genders">


                                    <option value="Woman">Woman</option>
                                    <option value="Man">Man</option>
                                </select>
                                @error('genders')
                                    <span class="invalid-feedback" role="alert">
                                        <strong>{{ $message }}</strong>
                                    </span>
                                @enderror
                            </div>
                        </div>




                        <div class="form-group row">
                            <label for="name" class="col-md-4 col-form-label text-md-right">{{ __('Name') }}</label>

                            <div class="col-md-6">
                                <input id="name" type="text" class="form-control @error('name') is-invalid @enderror" name="name" value="{{ old('name') }}" required autocomplete="name" autofocus>

                                @error('name')
                                    <span class="invalid-feedback" role="alert">
                                        <strong>{{ $message }}</strong>
                                    </span>
                                @enderror
                            </div>
                        </div>

                        <div class="form-group row">
                            <label for="email" class="col-md-4 col-form-label text-md-right">{{ __('E-Mail Address') }}</label>

                            <div class="col-md-6">
                                <input id="email" type="email" class="form-control @error('email') is-invalid @enderror" name="email" value="{{ old('email') }}" required autocomplete="email">

                                @error('email')
                                    <span class="invalid-feedback" role="alert">
                                        <strong>{{ $message }}</strong>
                                    </span>
                                @enderror
                            </div>
                        </div>

                        <div class="form-group row">
                            <label for="age" class="col-md-4 col-form-label text-md-right">{{ __('Age') }}</label>

                            <div class="col-md-6">
                                <select id="age" class="form-control @error('age') is-invalid @enderror" name="age" value="{{ old('age') }}" required autocomplete="age">
                                    <option value="18">18</option>
                                    <option value="19">19</option>
                                    <option value="20">20</option>
                                    <option value="21">21</option>
                                </select>
                                @error('age')
                                    <span class="invalid-feedback" role="alert">
                                        <strong>{{ $message }}</strong>
                                    </span>
                                @enderror
                            </div>
                        </div>

                        <div class="form-group row">
                            <label for="password" class="col-md-4 col-form-label text-md-right">{{ __('Password') }}</label>

                            <div class="col-md-6">
                                <input id="password" type="password" class="form-control @error('password') is-invalid @enderror" name="password" required autocomplete="new-password">

                                @error('password')
                                    <span class="invalid-feedback" role="alert">
                                        <strong>{{ $message }}</strong>
                                    </span>
                                @enderror
                            </div>
                        </div>

                        <div class="form-group row">
                            <label for="password-confirm" class="col-md-4 col-form-label text-md-right">{{ __('Confirm Password') }}</label>

                            <div class="col-md-6">
                                <input id="password-confirm" type="password" class="form-control" name="password_confirmation" required autocomplete="new-password">
                            </div>
                        </div>

                        <div class="form-group row mb-0">
                            <div class="col-md-6 offset-md-4">
                                <button type="submit" class="btn btn-primary">
                                    {{ __('Register') }}
                                </button>
                            </div>
                        </div>
                    </form>
                </div>
            </div>
        </div>
    </div>
</div>
@endsection

User.php

<?php

namespace App;

use Illuminate\Contracts\Auth\MustVerifyEmail;
use Illuminate\Foundation\Auth\User as Authenticatable;
use Illuminate\Notifications\Notifiable;

class User extends Authenticatable
{
    use Notifiable;

    /**
    * The attributes that are mass assignable.
    *
    * @var array
    */
    protected $fillable = [
        'gender_id', 'name', 'email', 'password', 'age',
    ];

    /**
    * The attributes that should be hidden for arrays.
    *
    * @var array
    */
    protected $hidden = [
        'password', 'remember_token',
    ];

    /**
    * The attributes that should be cast to native types.
    *
    * @var array
    */
    protected $casts = [
        'email_verified_at' => 'datetime',
    ];

    public function genders()
    {
        return $this->belongsTo(Gender::class);
    }
}

Answer 1

Eloquent relationship may not work if the column is not set properly.

In the migration the type of the column gender_id must be a unsignedBigInteger

I suggest you also to rename the function in your User.php model to gender instead of genders

I saw you use gender_id when you create your user:

$user = User::create([
            'genders_id' => $genders,
            'name' => $data['name'],
            'email' => $data['email'],
            'age' => $data['age'],
            'password' => Hash::make($data['password']),
]);

This will actually not work because Laravel will search for gender_id in the table

If you want to keep genders_id you can set your hasMany like this: return $this->hasMany(User::class, 'genders_id');

Answer 2

please chnage your model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Gender extends Model
{
    protected $fillable = [
        'gender_id',
    ];

    public function users()
    {
        return $this->hasMany(User::class);
    }
}