php - Laravel Eloquent create method causing integrity constraint violation -

i've got following eloquent models , relations set up:

applicant

class applicant {     public function application()     {         return $this->hasone(application::class);     } } 

application

class application {     public function applicant()     {         return $this->belongsto(applicant::class);     }      protected $fillable = [         // ... other fields         'applicant_id',     ]; } 

and migrations:

applicants table

public function up() {     schema::create('applicants', function (blueprint $table) {         $table->increments('id');         // other fields ...         }); } 

applications table

public function up() {     schema::create('applications', function (blueprint $table) {         $table->increments('id');         // other fields ...         $table->integer('applicant_id')->unsigned();          // other relations ...         $table->foreign('applicant_id')->references('id')->on('applications')->ondelete('cascade');     }); } 

i want create new applicant add new application applicant created:

$applicant = applicant::create([     // data ]);  $application = $applicant->applications()->create([     // data ]); 

however, when running code receive following error:

sqlstate[23000]: integrity constraint violation:  1452 cannot add or update child row: foreign key constraint fails (     `dbname`.`applications`, constraint `applications_applicant_id_foreign`      foreign key (`applicant_id`) references `applications` (`id`) on delete cascade ) (sql: insert `applications` (     `status`,     `reference_number`,     `organisation_id`,     `qualification_id`,     `applicant_id`,     `updated_at`,     `created_at` ) values (     pending,     573066ce59bfe,     24,     1,     12, // <------ applicant_id, i.e. foreign key!     2016-05-09 11:30:38,     2016-05-09 11:30:38 )) 

as understand, error occuring because i'm passing foreign key doesn't exist in database. wondering happening here first call db make create applicant:

$applicant = applicant::create([     // data ]); 

is not written db before second statement creates application:

$application = $applicant->application()->create([     // data ]); 

... , causing integrity constraint violation? because if dd($applicant) after creating or dd(applicant::find($applicant->id)) record , can view in db.

i've found prior re-factoring code when calling create() add new record building new application line line , using save(), didn't encounter issue. i'm curious know how both calls differ (if do) , correct way approach such scenario thought simple eloquent i've done many times before. advice appreciated, thanks!

edit 1

corrected call relation:

$applicant->application()->create(...)

not:

$applicant->applications()->create(...)

edit 2

running code:

$applicant = applicant::create($this->applicantdatafromrequest($request));  $application = new application([     'status'           => 'pending',     'reference_number' => $request->get('passport_number'),     'organisation_id'  => $request->get('organisation'),     'qualification_id' => $request->get('qualification') ?: null, ]);  $applicant->application()->save($application);  dd('done'); 

and receiving same error (updated errors on page):

sqlstate[23000]: integrity constraint violation: 1452 cannot add or update child row: foreign key constraint fails (`dbname`.`applications`, constraint `applications_applicant_id_foreign` foreign key (`applicant_id`) references `applications` (`id`) on delete cascade) (sql: insert `applications` (`status`, `reference_number`, `organisation_id`, `qualification_id`, `applicant_id`, `updated_at`, `created_at`) values (pending, 5730970933c7b, 24, 1, 22, 2016-05-09 14:56:25, 2016-05-09 14:56:25))  sqlstate[23000]: integrity constraint violation: 1452 cannot add or update child row: foreign key constraint fails (`dbname`.`applications`, constraint `applications_applicant_id_foreign` foreign key (`applicant_id`) references `applications` (`id`) on delete cascade) 

edit 3 added relevant migrations

update 1

really strange! i've reverted older version of project via git working before began re-factoring code , that's not working same reason! no clue what's going on here!?

update 2

just noticed silly in migrations:

applications table

public function up() {     schema::create('applications', function (blueprint $table) {         $table->increments('id');         // other fields ...         $table->integer('applicant_id')->unsigned();          // other relations ...         $table->foreign('applicant_id')->references('id')->on('applications')->ondelete('cascade');     }); } 

the foreign key should be:

$table->foreign('applicant_id')     ->references('id')     ->on('applicants')     ->ondelete('cascade'); // not applications! 

two points here:

1. why did not effect code til now? it's been working fine til weird...

2. going update foreign key constraint , try out see if works now

try this:

$applicant = new applicant([     // data ]);  $application = new application([     // data ]);  $applicant->applications()->save($application);