pre_schema_upgrade

函数
pre_schema_upgrade ( No parameters )

pre_schema_upgrade动作是一个钩子,在WordPress中运行模式升级过程之前被触发。这个动作是用来让插件和主题在模式升级过程运行之前执行任何必要的动作。

在模式升级前运行。

function pre_schema_upgrade() {
	global $wp_current_db_version, $wpdb;

	// Upgrade versions prior to 2.9.
	if ( $wp_current_db_version < 11557 ) {
		// Delete duplicate options. Keep the option with the highest option_id.
		$wpdb->query( "DELETE o1 FROM $wpdb->options AS o1 JOIN $wpdb->options AS o2 USING (`option_name`) WHERE o2.option_id > o1.option_id" );

		// Drop the old primary key and add the new.
		$wpdb->query( "ALTER TABLE $wpdb->options DROP PRIMARY KEY, ADD PRIMARY KEY(option_id)" );

		// Drop the old option_name index. dbDelta() doesn't do the drop.
		$wpdb->query( "ALTER TABLE $wpdb->options DROP INDEX option_name" );
	}

	// Multisite schema upgrades.
	if ( $wp_current_db_version < 25448 && is_multisite() && wp_should_upgrade_global_tables() ) {

		// Upgrade versions prior to 3.7.
		if ( $wp_current_db_version < 25179 ) {
			// New primary key for signups.
			$wpdb->query( "ALTER TABLE $wpdb->signups ADD signup_id BIGINT(20) NOT NULL AUTO_INCREMENT PRIMARY KEY FIRST" );
			$wpdb->query( "ALTER TABLE $wpdb->signups DROP INDEX domain" );
		}

		if ( $wp_current_db_version < 25448 ) {
			// Convert archived from enum to tinyint.
			$wpdb->query( "ALTER TABLE $wpdb->blogs CHANGE COLUMN archived archived varchar(1) NOT NULL default '0'" );
			$wpdb->query( "ALTER TABLE $wpdb->blogs CHANGE COLUMN archived archived tinyint(2) NOT NULL default 0" );
		}
	}

	// Upgrade versions prior to 4.2.
	if ( $wp_current_db_version < 31351 ) {
		if ( ! is_multisite() && wp_should_upgrade_global_tables() ) {
			$wpdb->query( "ALTER TABLE $wpdb->usermeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
		}
		$wpdb->query( "ALTER TABLE $wpdb->terms DROP INDEX slug, ADD INDEX slug(slug(191))" );
		$wpdb->query( "ALTER TABLE $wpdb->terms DROP INDEX name, ADD INDEX name(name(191))" );
		$wpdb->query( "ALTER TABLE $wpdb->commentmeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
		$wpdb->query( "ALTER TABLE $wpdb->postmeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
		$wpdb->query( "ALTER TABLE $wpdb->posts DROP INDEX post_name, ADD INDEX post_name(post_name(191))" );
	}

	// Upgrade versions prior to 4.4.
	if ( $wp_current_db_version < 34978 ) {
		// If compatible termmeta table is found, use it, but enforce a proper index and update collation.
		if ( $wpdb->get_var( "SHOW TABLES LIKE '{$wpdb->termmeta}'" ) && $wpdb->get_results( "SHOW INDEX FROM {$wpdb->termmeta} WHERE Column_name = 'meta_key'" ) ) {
			$wpdb->query( "ALTER TABLE $wpdb->termmeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
			maybe_convert_table_to_utf8mb4( $wpdb->termmeta );
		}
	}
}

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