RainLab\Builder\Classes\TableMigrationCodeGenerator::generateCreateOrUpdateDownCode PHP Method

    protected function generateCreateOrUpdateDownCode($tableDiff, $isNewTable, $newOrUpdatedTable)
    {
        $result = '';
        if ($isNewTable) {
            $result = $this->generateTableDropCode($tableDiff->name);
        } else {
            $changedPrimaryKey = $this->getChangedOrRemovedPrimaryKey($tableDiff);
            $addedPrimaryKey = $this->findPrimaryKeyIndex($tableDiff->addedIndexes, $newOrUpdatedTable);
            if ($this->tableHasNameOrColumnChanges($tableDiff) || $changedPrimaryKey || $addedPrimaryKey) {
                $hasColumnChanges = $this->tableHasNameOrColumnChanges($tableDiff, true);
                if ($tableDiff->getNewName()) {
                    $result .= $this->generateTableRenameCode($tableDiff->newName, $tableDiff->name);
                    if ($hasColumnChanges || $changedPrimaryKey || $addedPrimaryKey) {
                        $result .= $this->eol;
                    }
                }
                if (!$hasColumnChanges && !$changedPrimaryKey && !$addedPrimaryKey) {
                    return $this->makeTabs($result);
                }
                $result .= $this->generateSchemaTableMethodStart($tableDiff->name, $isNewTable);
                if ($changedPrimaryKey || $addedPrimaryKey) {
                    $result .= $this->generatePrimaryKeyDrop($newOrUpdatedTable);
                }
                foreach ($tableDiff->addedColumns as $column) {
                    $result .= $this->generateColumnDrop($column);
                }
                foreach ($tableDiff->changedColumns as $columnDiff) {
                    $result .= $this->generateColumnCode($columnDiff, self::COLUMN_MODE_REVERT);
                }
                foreach ($tableDiff->renamedColumns as $oldName => $column) {
                    $result .= $this->generateColumnRenameCode($column->getName(), $oldName);
                }
                foreach ($tableDiff->removedColumns as $name => $column) {
                    $result .= $this->generateColumnCode($column, self::COLUMN_MODE_CREATE);
                }
                if ($changedPrimaryKey || $addedPrimaryKey) {
                    $primaryKey = $this->findPrimaryKeyIndex($tableDiff->fromTable->getIndexes(), $tableDiff->fromTable);
                    if ($primaryKey) {
                        $result .= $this->generatePrimaryKeyCode($primaryKey, self::COLUMN_MODE_CREATE);
                    }
                }
                $result .= $this->generateSchemaTableMethodEnd();
            }
        }
        return $this->makeTabs($result);
    }