laravel and artisan error cannot add foreign key on migrate - php

Question

I know this has been answered many times as i saw many answers suggestions when i wrote the question, but none of them actually get me the correct answer.
When i try to add new field to the table and use artisan migrate in laravel i get an error
General error: 1215 Cannot add foreign key constraint (SQL: alter table `pages` add constraint pages_page_status_foreign foreign key (`page_status`) references `page_status` (`status_value`))
But i don't understand why do i get an error when before i have done the same thing and with no errors, only answer i could think of is that it's not possible to have two or more foreign keys on same table. Here is my migrate function
class CreateStatusTable extends Migration {
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::create('page_status', function($table) {
$table->increments('id');
$table->string('status_name');
$table->integer('status_value')->unsigned();
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::drop('page_status');
}
}
This is for status table, and now i have to add new field to pages table using this.
class AddStatusToPagesTable extends Migration {
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::table('pages', function($table) {
$table->integer('page_status')->unsigned();
$table->foreign('page_status')->references('status_value')->on('page_status');
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::table('pages', function($table) {
$table->dropForeign('pages_page_status_foreign');
});
}
}
And this is where the error appears, for some reason it does not let me set foreign key on page_status field into pages table.
I am using xampp installation on my localhost and in phpmyadmin i can see that table is set to innodb, actually everything is set to innodb by default. and inside my database in pages table looking at page_status field i have first to set it index than i am able to use relations. why it's not set to index i don't know but i already have on that table id as an index and author as foreign key.
Before this i also added few fields when creating pages table and using this
class CreatePagesTable extends Migration {
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::create('pages', function($table){
$table->increments('id');
$table->integer('author')->unsigned();
$table->foreign('author')->references('id')->on('users');
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::drop('pages');
}
}
I did not had any problems when using migrate, it worked well and author is set as foreign key.
So why i can't add new foreign key now ?

Answer 1

This is probably due to the fact that a foreign key can't be added if the current records do not meet the condition. If page_status is optional make the field nullable:
$table->integer('page_status')->unsigned()->nullable();
If you don't want to make it nullable and are going to insert valid foreign key values later you can disable foreign key checks temporarily:
DB::statement('SET FOREIGN_KEY_CHECKS = 0');
Schema::table('pages', function($table) {
$table->integer('page_status')->unsigned();
$table->foreign('page_status')->references('status_value')->on('page_status');
});
DB::statement('SET FOREIGN_KEY_CHECKS = 1');

Answer 2

I found where the problem is, after adding a new field to the table you have to set the index on that field, so there is a one step further on migration for setting the field as index.
I still do not understand why in my first migration when i added "author" field it made it automatically as an index but for this one i got it working by setting index additionally like this:
Schema::table('pages', function($table) {
$table->integer('status')->unsigned()->nullable();
$table->index('status');
$table->foreign('status')->references('status_value')->on('page_status');
});