Fix sorting in dropdown (#187)

* fix: fix order of page categories with raw type

* refactor: change method location and others

* refactor: fix method names and variables also split methods to be clear their role

* fix: fix variable name

* fix: change the method to group of pages

* refactor: replace filter metethod to querying database

* refactor: fix typo, rename variable, add comments, improve code quality

* fix: add exit infinite loop

* fix: replace exiting loop to throwing exception

src/backend/models/pageOrder.ts

@@ -75,6 +75,28 @@ class PageOrder {
     return Promise.all(docs.map(doc => new PageOrder(doc)));
   }
 
+  /**
+   * Returns only root page's order
+   *
+   * @returns {Promise<PageOrder[]>}
+   */
+  public static async getRootPageOrder(): Promise<PageOrder> {
+    const docs = await db.findOne({ 'page': '0' });
+
+    return new PageOrder(docs);
+  }
+
+  /**
+   * Returns only child page's order
+   *
+   * @returns {Promise<PageOrder[]>}
+   */
+  public static async getChildPageOrder(): Promise<PageOrder[]> {
+    const docs = await this.getAll({ 'page': { $ne: '0' } });
+
+    return Promise.all(docs.map(doc => new PageOrder(doc)));
+  }
+
   /**
    * constructor data setter
    *