Foreign key constraint error when refreshing migrations - Laravel - php

Question

I'm having a problem with migration on my Laravel project.
Since i'm fairly new to Laravel I can't figure it out.
I want to add a foreign key to an already existing table and this works, but when I refresh my migrations I get this error:
[Illuminate\Database\QueryException]
SQLSTATE[23000]: Integrity constraint violation: 1217 Cannot delete or update a parent row: a foreign key
constraint fails (SQL: drop table `battles`)
[PDOException]
SQLSTATE[23000]: Integrity constraint violation: 1217 Cannot delete or update a parent row: a foreign key
constraint fails
These are the migrations I currently have:
Table Projects
class CreateProjectsTable extends Migration
{
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::create('projects', function (Blueprint $table) {
$table->increments('id');
$table->string('title');
$table->string('body');
$table->string('tags');
$table->string('img');
$table->string('img_tricolor');
$table->integer('user_id')->unsigned();
$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
$table->timestamps();
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::drop('projects');
}
}
Table Battles
class CreateBattlesTable extends Migration
{
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::create('battles', function (Blueprint $table) {
$table->increments('id');
$table->string('battle_theme');
$table->boolean('battle_active');
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::drop('battles');
}
}
Adding foreign key for battles in projects
class AddProjectsBattleIdFk extends Migration
{
/**
* Run the migrations.
*
* #return void
*/
public function up()
{
Schema::table('projects', function (Blueprint $table) {
$table->integer('battle_id')->unsigned();
$table->foreign('battle_id')->references('id')->on('battles')->onDelete('set null');
});
}
/**
* Reverse the migrations.
*
* #return void
*/
public function down()
{
Schema::table('projects', function (Blueprint $table) {
//
});
}
}
I suppose it has something to do with the battles table.

Answer 1

In down methods you need to remove foreign keys first:
In CreateProjectsTable
public function down()
{
Schema::table('projects', function (Blueprint $table) {
$table->dropForeign('projects_user_id_foreign');
});
Schema::drop('projects');
}
In AddProjectsBattleIdFk
public function down()
{
Schema::table('projects', function (Blueprint $table) {
$table->dropForeign('projects_battle_id_foreign');
$table->dropColumn('battle_id');
});
}

Answer 2

I had the same problem,the Marcin's answer worked but I also found that another option is using fresh instead of refresh, in that case you don't need to remove foreign keys.

Answer 3

I don't know if this is more updated solution will help someone that is facing the same problem:
use this in your migration down function
Schema::disableForeignKeyConstraints();
I usually create as the last migration or name it to be sorted as last (cause migration comand runs the files under migration folder by order) something like 2099_12_32_AlterTablesCreateForeignKeysmigration where in the up function I specify all my keys for every table and at the end enable foreign keys constraints Schema::enableForeignKeyConstraints(); and then then in the down i just disabled them Schema::disableForeignKeyConstraints(); to allow the reset to truncate the tables.