Doctrine migration and fixtures error - symfony

Question

I execute migrations to create the database, after that, I want to fill database with some data. Why generate id strategy is not working?
bin/console doctrine:migrations:migrate
Migrations
WARNING! You are about to execute a database migration that could result in schema changes and data lost. Are you sure you wish to continue? (y/n)y
Migrating up to 20160510103145 from 0
++ migrating 20160510103145
-> CREATE TABLE navieras (id INTEGER NOT NULL, nombre VARCHAR(255) NOT NULL)
++ migrated (0.14s)
------------------------
++ finished in 0.14s
++ 1 migrations executed
++ 1 sql queries
bin/console doctrine:fixtures:load
Careful, database will be purged. Do you want to continue y/N ?y
> purging database
> loading AppBundle\DataFixtures\ORM\LoadNavieraData
[Doctrine\DBAL\Exception\NotNullConstraintViolationException]
An exception occurred while executing 'INSERT INTO navieras (nombre) VALUES (?)' with params ["Royal Caribbean"]:
SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: navieras.id
[Doctrine\DBAL\Driver\PDOException]
SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: navieras.id
[PDOException]
SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: navieras.id
Fixture load function
public function load(ObjectManager $manager)
{
$naviera = new Naviera();
$naviera->setNombre('aaaaaaaaaaaaaaa');
$naviera2 = new Naviera();
$naviera2->setNombre('bbbbbbbbbbbbbb');
$manager->persist($naviera);
$manager->persist($naviera2);
$manager->flush();
}
Migration
public function up(Schema $schema)
{
$navieras = $schema->createTable('navieras');
$navieras->addColumn('id', "integer");
$navieras->addColumn('nombre', "string");
}
/**
* #param Schema $schema
*/
public function down(Schema $schema)
{
$schema->dropTable('navieras');
}
Naviera Entity
/**
* Modelo naviera
*
* #Entity
* #Table(name="navieras")
*/
class Naviera
{
/**
* #Id
* #Column(type="integer")
* #GeneratedValue
*/
private $id;
/**
* #Column(type="string");
*/
private $nombre;
/**
* #return integer
*/
public function getId()
{
return $this->id;
}
/**
* #param integer $id
*/
public function setId($id)
{
$this->$id = $id;
}
/**
* #return string
*/
public function getNombre()
{
return $this->nombre;
}
/**
* #param string $nombre
*/
public function setNombre($nombre)
{
$this->nombre = $nombre;
}
}
I'm using SQLite

Answer 1

Your migration up does not create an auto incrementing id column. Just an integer column. If you change your migration up function to the following it should fix your issue:
public function up(Schema $schema)
{
$navieras = $schema->createTable('navieras');
$navieras->addColumn('id', 'integer', ['Autoincrement' => true]);
$navieras->addColumn('nombre', 'string');
$navieras->setPrimaryKey('id', true);
}