laravel migration error while adding 2 foreign key - mysql

Question

I am using Laravel migrations to create my MySQL database, and have two tables papers and answers, and need to connect both tables using foreign keys. I have the paper_id as well as question_no as the foreign keys. but when adding foreign key I get an error.
My migration for paper table and answer table
Schema::create('exampapers', function (Blueprint $table) {
$table->engine = 'InnoDB';
$table->increments('id');
$table->integer('paper_id');
$table->integer('question_no');
$table->text('question');
$table->string('answer1');
$table->string('answer2');
$table->string('answer3');
$table->string('answer4');
$table->integer('answerC');
$table->string('knowarea');
$table->timestamps();
$table->index(['paper_id','question_no']);
});
Schema::create('answers', function (Blueprint $table) {
$table->engine = 'InnoDB';
$table->increments('id');
$table->integer('paper')->unsigned();
$table->integer('question')->unsigned();
$table->integer('answers');
$table->timestamps();
});
and this is my code for creating foreign keys,
Schema::table('answers',function($table){
$table->foreign('paper')->references('paper_id')->on('exampapers');
$table->foreign('question')->references('question_no')->on('exampapers');
});
The error I get through php artisan is,
Illuminate\Database\QueryException : SQLSTATE[HY000]: General error:
1005
Can't create table exam_paper.#sql-b88_630 (errno: 150 "Foreign key
constraint is incorrectly formed") (SQL: alter table answers add
constraint answers_paper_foreign
foreign key (paper) references exampapers (paper_id))
I referred most of the other posts and already tried unsignedInteger() data type, running the table creation before foreign key creation.
What am I doing wrong in my code?

Answer 1

You need to add ->unsigned()->nullable()->index(); in both column (i.e. in paper_id and in question in exampapers table).
Try to add like below in exampapers table:
$table->integer('paper_id')->unsigned()->nullable()->index();
$table->integer('question_no')->unsigned()->nullable()->index();
Now run php artisan migrate and problem fixed!
Hope this helps you!

Answer 2

You need to make the key in the exampapers table unsigned too:
$table->integer('paper_id')->unsigned();
Or:
$table->insignedInteger('paper_id');
Or remove the unsigned() method from the foreign key definition:
$table->integer('paper');

Answer 3

I have made some edits to your migration code. Hope this will work
Schema::create('exampapers', function (Blueprint $table) {
$table->engine = 'InnoDB';
$table->increments('id');
$table->integer('paper_id')->unsigned()->index();
$table->integer('question_no')->unsigned()->index();
$table->text('question');
$table->string('answer1');
$table->string('answer2');
$table->string('answer3');
$table->string('answer4');
$table->integer('answerC');
$table->string('knowarea');
$table->timestamps();
//$table->index(['paper_id','question_no']);
});
Schema::create('answers', function (Blueprint $table) {
$table->engine = 'InnoDB';
$table->increments('id');
$table->integer('paper')->unsigned()->index();
$table->integer('question')->unsigned()->index();
$table->integer('answers');
$table->timestamps();
});
Schema::table('answers',function($table){
$table->foreign('paper')->references('paper_id')->on('exampapers');
$table->foreign('question')->references('question_no')->on('exampapers');
});