Always generate db tag (either from dbname or name)

sam/_gen.php

@@ -81,3 +81,13 @@ foreach (array("routes") as $type) {
 
 	file_put_contents($filename, $contents);
 }
+
+// camel case to snake case
+function decamel($input) {
+  preg_match_all('!([A-Z][A-Z0-9]*(?=$|[A-Z][a-z0-9])|[A-Za-z][a-z0-9]+)!', $input, $matches);
+  $ret = $matches[0];
+  foreach ($ret as &$match) {
+    $match = $match == strtoupper($match) ? strtolower($match) : lcfirst($match);
+  }
+  return implode('_', $ret);
+}

sam/templates/http_structs.tpl

@@ -20,7 +20,7 @@ type ({foreach $structs as $struct}
 	// {api.title}
 	{struct.name} struct {
 {foreach $struct.fields as $field}
-		{field.name} {field.type}{if $field.tag || $field.dbname} `{$field.tag}{if $field.dbname} db:"{$field.dbname}"{/if}`{/if}{newline}
+		{field.name} {field.type} `{if $field.tag}{$field.tag} {/if}db:"{if $field.dbname}{$field.dbname}{else}{$field.name|decamel}{/if}"`{newline}
 {/foreach}
 
 		changed []string