Added simple database evolutions to ease future database changes

evolutions/001-event-initiator.sql

@@ -0,0 +1,3 @@
+alter table `event` add column `initiator` bigint(20);
+alter table `event` add constraint `e_f_initiator`
+      foreign key(`initiator`) references `user`(`id`);

include/functions.php

@@ -312,6 +312,42 @@ if($db->connect_errno) {
     $error = 'Failed to connect to db. The error was: '.$db->connect_error;
     throw new Exception($error);
 }
+evolve_db();
+
+function evolve_db() {
+    global $db;
+
+    $init = prepare(<<<SQL
+        create table if not exists `evolutions`
+        (`filename` varchar(64) not null,
+         primary key(`filename`),
+         `apply_date` bigint(20) not null,
+         `index` bigint(20) not null auto_increment,
+         key(`index`))
+    SQL);
+    execute($init);
+
+    $applied = prepare('select `filename`, `index` from `evolutions`');
+    execute($applied);
+    $applied_files = array();
+    foreach(result_list($applied) as $row) {
+        $applied_files[$row['filename']] = $row['index'];
+    }
+
+    begin_trans();
+    foreach(glob("./evolutions/*.sql") as $path) {
+        $filename = basename($path);
+        if(!array_key_exists($filename, $applied_files)) {
+            $db->multi_query(file_get_contents($path));
+            $save = prepare('insert into `evolutions`
+                                 (`filename`, `apply_date`)
+                                 values (?, ?)');
+            bind($save, 'si', $filename, time());
+            execute($save);
+        }
+    }
+    commit_trans();
+}
 
 function prepare($statement) {
     global $db;