Add custom string index support

- Added custom string index support
- Optimized calculating logical expressions with return-early pattern
- Fixed: return value only checked if the index was an array

lib/metadata.js

@@ -61,14 +61,18 @@ class Options {
 class Indexes {
   extract(key, field) {
     const { index, primary, unique, many } = field;
-    const isIndex = Array.isArray(index || primary || unique);
-    const isStringIndex =
-      typeof index === 'string' &&
-      index.indexOf('(') !== -1 &&
-      index.lastIndexOf(')') !== -1 &&
-      index.substring(index.indexOf('('), index.lastIndexOf(')')).trim()
-        .length !== 0;
-    if (isIndex || isStringIndex || many) this[key] = field;
+    const chosenIndex = index || primary || unique;
+    const isStringIndex = (index) => {
+      if (typeof index !== 'string') return false;
+      if (index.indexOf('(') === -1 && index.indexOf(')') === -1) return false;
+      const expression = index.substring(
+        index.indexOf('(') + 1,
+        index.lastIndexOf(')'),
+      );
+      return expression.trim().length !== 0;
+    };
+    const isIndex = Array.isArray(chosenIndex) || isStringIndex(chosenIndex);
+    if (isIndex || many) this[key] = field;
     return isIndex;
   }
 }