While running the installation of a module, there are four files executed to create schemas and insert data. To create schemas, the files used are as follows:

Setup/InstallSchema.php

Setup/UpgradeSchema.php

The installation file is executed only when there is no record in the setup_module table for the module. The upgrade file is executed only when the current version number in the setup_module table is lower than the version configured in your etc/module.xml file.

When it's necessary to insert default values into a table or new EAV attributes need to be created, these actions need to be configured in the following files:

Setup/InstallData.php

Setup/UpgradeData.php

Magento keeps track of which version is installed for an extension in the setup_module table; here, the current installed version for the schema and data is stored:

Follow these steps to create your database tables:

In Magento 2, the running of the setup scripts is no longer triggered by the first request after flushing the cache; to initiate the running of these scripts, run the command specified in step 2. When running the upgrade command, all modules are evaluated on their current version and module version in the configuration file. First, all schema installations/updates are executed, and next, the data installations/updates are processed.

The InstallData and InstallSchema files are executed only when there is no prior registration of the extension in the setup_module table. To run the installation files during testing, it is possible to remove the module row from the table and run the bin/magento setup:upgrade command.

The available methods to create a new table are defined in the MagentoFrameworkDBAdapterAdapterInterfaceTable class and are as follows:

When changing an existing table, it is possible to use the following methods; these are the methods that can be used directly on the $installer->getConnection() class:

When, in a later version of the extension, there are extra fields necessary (or the current fields need to be changed), this is handled through the UpgradeSchema function, upgrade:

Setup/UpgradeSchema.php

<?php
namespace GenmatoSampleSetup;

use MagentoFrameworkDBDdlTable;
use MagentoFrameworkSetupUpgradeSchemaInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoFrameworkSetupSchemaSetupInterface;

class UpgradeSchema implements UpgradeSchemaInterface
{
  public function upgrade(SchemaSetupInterface $setup, ModuleContextInterface $context)
  {
    $setup->startSetup();

    if (version_compare($context->getVersion(), '0.1.1', '<')) {
      $connection = $setup->getConnection();

      $column = [
        'type' => Table::TYPE_SMALLINT,
        'length' => 6,
        'nullable' => false,
        'comment' => 'Is Visible',
        'default' => '1'
      ];
      $connection->addColumn($setup->getTable('genmato_demo'), 'is_visible', $column);
    }

    $setup->endSetup();
  }
}

As this file is run every time the module version is different than the currently installed version, it is necessary to check the current version that is installed to execute only the updates necessary:

if (version_compare($context->getVersion(), '0.1.1', '<')) {

The preceding statement will make sure that the schema changes are executed only if the current version is less than 0.1.1.

<?php
namespace GenmatoSampleSetup;

use GenmatoSampleModelDemo;
use GenmatoSampleModelDemoFactory;
use MagentoFrameworkSetupInstallDataInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoFrameworkSetupModuleDataSetupInterface;

class InstallData implements InstallDataInterface
{
  /**
  * Demo factory
  *
  * @var DemoFactory
  */
  private $demoFactory;

  /**
  * Init
  *
  * @param DemoFactory $demoFactory
  */
  public function __construct(DemoFactory $demoFactory)
  {
    $this->demoFactory = $demoFactory;
  }

  /**
  * {@inheritdoc}
  * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
  */
  public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
  {
    $demoData = [
      'title' => 'Demo Title',
      'is_active' => 1,
    ];

    /**
    * Insert demo data
    */
    $this->createDemo()->setData($demoData)->save();

  }

  /**
  * Create demo
  *
  * @return Demo
  */
  public function createDemo()
  {
    return $this->demoFactory->create();
  }
}

$this->demoFactory->create();