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<?php
class Migrator {
private $Database;
private $version;
private $directory;
private $migrations = [];
const CURRENT_SCHEMA_VERSION = 5;
#===============================================================================
# Fetch on-disk schema version from migration table
#===============================================================================
public function __construct(Database $Database) {
$this->Database = $Database;
try {
$Statement = $Database->query('SELECT schema_version FROM migration');
# Explicitly check for FALSE, because result can be "0"
if(($this->version = $Statement->fetchColumn()) === FALSE) {
throw new Exception('The migration table does exist, but there is
no row containing the currently used on-disk schema version!');
}
} catch(PDOException $Exception) {
if($Exception->getCode() === '42S02') /* Table not found */ {
$this->version = $this->determineFallbackSchemaVersion();
$this->createMigrationTable($this->version);
} else {
throw $Exception;
}
}
}
#===============================================================================
# Specify the directory which contains the migration files
#===============================================================================
public function setMigrationsDir(string $directory): void {
if(!is_readable($this->directory = rtrim($directory, '/'))) {
throw new Exception('Migrator cannot read migration directory.');
};
}
#===============================================================================
# Check if new migrations needs to be applied
#===============================================================================
public function isMigrationNeeded(): bool {
$databaseSchema = $this->version;
$codebaseSchema = self::CURRENT_SCHEMA_VERSION;
return $databaseSchema < $codebaseSchema;
}
#===============================================================================
# Check if this is an unsupported downgrade attempt
#===============================================================================
public function isDowngradeAttempt(): bool {
$databaseSchema = $this->version;
$codebaseSchema = self::CURRENT_SCHEMA_VERSION;
return $databaseSchema > $codebaseSchema;
}
#===============================================================================
# Add a migration to the queue
#===============================================================================
private function enqueue(int $sequence, string $migration): void {
$this->migrations[$sequence] = $migration;
}
#===============================================================================
# Remove a migration from the queue
#===============================================================================
private function dequeue(int $sequence): void {
unset($this->migrations[$sequence]);
}
#===============================================================================
# Get the currently used on-disk schema version
#===============================================================================
public function getVersionFromTable(): int {
return $this->version;
}
#===============================================================================
# Get an array with all migration commands
#===============================================================================
public function getMigrations(): array {
$databaseSchema = $this->version;
$codebaseSchema = self::CURRENT_SCHEMA_VERSION;
if(!$this->isMigrationNeeded()) {
return [];
}
foreach(range($databaseSchema+1, $codebaseSchema) as $number) {
$file = sprintf("%s/%d.sql", $this->directory, $number);
if(!is_readable($file)) {
throw new Exception("Migrator cannot read migration file: »{$file}«");
}
$this->enqueue($number, file_get_contents($file));
}
return $this->migrations;
}
#===============================================================================
# Run migrations sequentially
#===============================================================================
public function runMigrations(): array {
foreach($this->getMigrations() as $sequence => $migration) {
try {
if($this->Database->query($migration)) {
$this->dequeue($sequence);
$this->updateMigrationTable($sequence);
$migrated[] = $sequence;
}
} catch(PDOException $Exception) {
$error = 'Migration from %d to %d failed with PDO error:<br>';
$error .= sprintf($error, $sequence-1, $sequence);
$error .= sprintf('<code>%s</code>', $Exception->getMessage());
if(!empty($migrated ?? [])) {
$error .= '<br>The following migrations were successful: ';
$error .= '<code>'.implode(', ', $migrated).'</code>';
}
throw new Exception($error);
}
}
return $migrated ?? [];
}
#===============================================================================
# Update the migration table with the specified schema version
#===============================================================================
private function updateMigrationTable(int $version): int {
$query = 'UPDATE migration SET schema_version = ?';
$Statement = $this->Database->prepare($query);
if($Statement->execute([$version])) {
return $this->version = $version;
}
}
#===============================================================================
# Create the migration table with the specified schema version
#===============================================================================
private function createMigrationTable(int $version): bool {
$create = 'CREATE TABLE migration (schema_version smallint(4) NOT NULL)
ENGINE=InnoDB DEFAULT CHARSET=utf8mb4';
$insert = 'INSERT INTO migration (schema_version) VALUES (?)';
$this->Database->query($create);
$Statement = $this->Database->prepare($insert);
return $Statement->execute([$version]);
}
#===============================================================================
# Determine on-disk schema version if migration table does not exist
#===============================================================================
private function determineFallbackSchemaVersion(): int {
# If the migration table does not yet exist, the user may have upgraded from
# an older release of the application and sits somewhere between 0 and 4. So
# we run some checks against the tables to determine the schema version.
$test[4] = 'SHOW COLUMNS FROM post WHERE Field = "argv" AND Type = "varchar(250)"';
$test[3] = 'SHOW INDEX FROM post WHERE Key_name = "search"';
$test[2] = 'SHOW INDEX FROM post WHERE Key_name = "time_insert"';
$test[1] = 'SHOW COLUMNS FROM post WHERE Field = "argv"';
foreach($test as $version => $query) {
try {
$Statement = $this->Database->query($query);
if ($Statement && $Statement->fetch()) {
return $version;
}
} catch(PDOException $Exception) {}
}
return 0;
}
}
|
