PMA\libraries\Table::updateForeignKeys PHP Method

    public function updateForeignKeys($destination_foreign_db, $multi_edit_columns_name, $destination_foreign_table, $destination_foreign_column, $options_array, $table, $existrel_foreign)
    {
        $html_output = '';
        $preview_sql_data = '';
        $display_query = '';
        $seen_error = false;
        foreach ($destination_foreign_db as $master_field_md5 => $foreign_db) {
            $create = false;
            $drop = false;
            // Map the fieldname's md5 back to its real name
            $master_field = $multi_edit_columns_name[$master_field_md5];
            $foreign_table = $destination_foreign_table[$master_field_md5];
            $foreign_field = $destination_foreign_column[$master_field_md5];
            if (isset($existrel_foreign[$master_field_md5]['ref_db_name'])) {
                $ref_db_name = $existrel_foreign[$master_field_md5]['ref_db_name'];
            } else {
                $ref_db_name = $GLOBALS['db'];
            }
            $empty_fields = false;
            foreach ($master_field as $key => $one_field) {
                if (!empty($one_field) && empty($foreign_field[$key]) || empty($one_field) && !empty($foreign_field[$key])) {
                    $empty_fields = true;
                }
                if (empty($one_field) && empty($foreign_field[$key])) {
                    unset($master_field[$key]);
                    unset($foreign_field[$key]);
                }
            }
            if (!empty($foreign_db) && !empty($foreign_table) && !$empty_fields) {
                if (isset($existrel_foreign[$master_field_md5])) {
                    $constraint_name = $existrel_foreign[$master_field_md5]['constraint'];
                    $on_delete = !empty($existrel_foreign[$master_field_md5]['on_delete']) ? $existrel_foreign[$master_field_md5]['on_delete'] : 'RESTRICT';
                    $on_update = !empty($existrel_foreign[$master_field_md5]['on_update']) ? $existrel_foreign[$master_field_md5]['on_update'] : 'RESTRICT';
                    if ($ref_db_name != $foreign_db || $existrel_foreign[$master_field_md5]['ref_table_name'] != $foreign_table || $existrel_foreign[$master_field_md5]['ref_index_list'] != $foreign_field || $existrel_foreign[$master_field_md5]['index_list'] != $master_field || $_REQUEST['constraint_name'][$master_field_md5] != $constraint_name || $_REQUEST['on_delete'][$master_field_md5] != $on_delete || $_REQUEST['on_update'][$master_field_md5] != $on_update) {
                        // another foreign key is already defined for this field
                        // or an option has been changed for ON DELETE or ON UPDATE
                        $drop = true;
                        $create = true;
                    }
                    // end if... else....
                } else {
                    // no key defined for this field(s)
                    $create = true;
                }
            } elseif (isset($existrel_foreign[$master_field_md5])) {
                $drop = true;
            }
            // end if... else....
            $tmp_error_drop = false;
            if ($drop) {
                $drop_query = 'ALTER TABLE ' . Util::backquote($table) . ' DROP FOREIGN KEY ' . Util::backquote($existrel_foreign[$master_field_md5]['constraint']) . ';';
                if (!isset($_REQUEST['preview_sql'])) {
                    $display_query .= $drop_query . "\n";
                    $this->_dbi->tryQuery($drop_query);
                    $tmp_error_drop = $this->_dbi->getError();
                    if (!empty($tmp_error_drop)) {
                        $seen_error = true;
                        $html_output .= Util::mysqlDie($tmp_error_drop, $drop_query, false, '', false);
                        continue;
                    }
                } else {
                    $preview_sql_data .= $drop_query . "\n";
                }
            }
            $tmp_error_create = false;
            if (!$create) {
                continue;
            }
            $create_query = $this->_getSQLToCreateForeignKey($table, $master_field, $foreign_db, $foreign_table, $foreign_field, $_REQUEST['constraint_name'][$master_field_md5], $options_array[$_REQUEST['on_delete'][$master_field_md5]], $options_array[$_REQUEST['on_update'][$master_field_md5]]);
            if (!isset($_REQUEST['preview_sql'])) {
                $display_query .= $create_query . "\n";
                $this->_dbi->tryQuery($create_query);
                $tmp_error_create = $this->_dbi->getError();
                if (!empty($tmp_error_create)) {
                    $seen_error = true;
                    if (substr($tmp_error_create, 1, 4) == '1005') {
                        $message = Message::error(__('Error creating foreign key on %1$s (check data ' . 'types)'));
                        $message->addParam(implode(', ', $master_field));
                        $html_output .= $message->getDisplay();
                    } else {
                        $html_output .= Util::mysqlDie($tmp_error_create, $create_query, false, '', false);
                    }
                    $html_output .= Util::showMySQLDocu('InnoDB_foreign_key_constraints') . "\n";
                }
            } else {
                $preview_sql_data .= $create_query . "\n";
            }
            // this is an alteration and the old constraint has been dropped
            // without creation of a new one
            if ($drop && $create && empty($tmp_error_drop) && !empty($tmp_error_create)) {
                // a rollback may be better here
                $sql_query_recreate = '# Restoring the dropped constraint...' . "\n";
                $sql_query_recreate .= $this->_getSQLToCreateForeignKey($table, $master_field, $existrel_foreign[$master_field_md5]['ref_db_name'], $existrel_foreign[$master_field_md5]['ref_table_name'], $existrel_foreign[$master_field_md5]['ref_index_list'], $existrel_foreign[$master_field_md5]['constraint'], $options_array[$existrel_foreign[$master_field_md5]['on_delete']], $options_array[$existrel_foreign[$master_field_md5]['on_update']]);
                if (!isset($_REQUEST['preview_sql'])) {
                    $display_query .= $sql_query_recreate . "\n";
                    $this->_dbi->tryQuery($sql_query_recreate);
                } else {
                    $preview_sql_data .= $sql_query_recreate;
                }
            }
        }
        // end foreach
        return array($html_output, $preview_sql_data, $display_query, $seen_error);
    }

 /**
  * Update for FK
  *
  * @return void
  */
 public function updateForForeignKeysAction()
 {
     $multi_edit_columns_name = isset($_REQUEST['foreign_key_fields_name']) ? $_REQUEST['foreign_key_fields_name'] : null;
     // (for now, one index name only; we keep the definitions if the
     // foreign db is not the same)
     list($html, $preview_sql_data, $display_query, $seen_error) = $this->upd_query->updateForeignKeys($_POST['destination_foreign_db'], $multi_edit_columns_name, $_POST['destination_foreign_table'], $_POST['destination_foreign_column'], $this->options_array, $this->table, isset($this->existrel_foreign) ? $this->existrel_foreign['foreign_keys_data'] : null);
     $this->response->addHTML($html);
     // If there is a request for SQL previewing.
     if (isset($_REQUEST['preview_sql'])) {
         PMA_previewSQL($preview_sql_data);
     }
     if (!empty($display_query) && !$seen_error) {
         $GLOBALS['display_query'] = $display_query;
         $this->response->addHTML(Util::getMessage(__('Your SQL query has been executed successfully.'), null, 'success'));
     }
 }