Migrate to HttpClient in Operation module.

src/operations/category.service.ts

@@ -5,14 +5,14 @@ import * as moment from 'moment';
 import { Injectable } from '@angular/core';
 import { Observable } from 'rxjs/Rx';
 
-import { Restangular } from "ngx-restangular";
+import { HttpClient, HttpParams } from "@angular/common/http";
 
 import { Category } from './category';
 
 @Injectable()
 export class CategoryService {
   constructor(
-    private restangular: Restangular
+    private http: HttpClient
   ) {}
 
   formatDate(date: Date|string) {
@@ -24,16 +24,16 @@ export class CategoryService {
   }
 
   query(id: number, minDate: Date = null, maxDate: Date = null): Observable<Category[]> {
-    var dateRange: any = {};
+    let params: HttpParams = new HttpParams();
 
     if(minDate) {
-      dateRange.begin = this.formatDate(minDate);
+      params = params.set('begin', this.formatDate(minDate));
     }
 
     if(maxDate) {
-      dateRange.end = this.formatDate(maxDate);
+      params = params.set('end', this.formatDate(maxDate));
     }
 
-    return this.restangular.one('account', id).getList('category', dateRange);
+    return this.http.get<Category[]>(`/api/account/${id}/category`, { params: params});
   }
 }