Add sorting by multiple criteria option

Closes #29

README.md

@@ -348,12 +348,14 @@ The `options` param can have the following (optional) fields:
 
 ```javascript
 const options = {
-  sortBy: 'name:desc',
-  limit: 5,
-  page: 2,
+  sortBy: 'name:desc', // sort order
+  limit: 5, // maximum results per page
+  page: 2, // page number
 };
 ```
 
+The plugin also supports sorting by multiple criteria (separated by a comma): `sortBy: name:desc,role:asc`
+
 The `paginate` method returns a Promise, which fulfills with an object having the following properties:
 
 ```json

src/models/plugins/paginate.plugin.js

@@ -13,17 +13,22 @@ const paginate = (schema) => {
    * Query for documents with pagination
    * @param {Object} [filter] - Mongo filter
    * @param {Object} [options] - Query options
-   * @param {string} [options.sortBy] - Sort option in the format: sortField:(desc|asc)
+   * @param {string} [options.sortBy] - Sorting criteria using the format: sortField:(desc|asc). Multiple sorting criteria should be separated by commas (,)
    * @param {number} [options.limit] - Maximum number of results per page (default = 10)
    * @param {number} [options.page] - Current page (default = 1)
    * @returns {Promise<QueryResult>}
    */
   schema.statics.paginate = async function (filter, options) {
-    const sort = {};
+    let sort = '';
     if (options.sortBy) {
-      const parts = options.sortBy.split(':');
-      sort[parts[0]] = parts[1] === 'desc' ? -1 : 1;
+      const sortingCriteria = [];
+      options.sortBy.split(',').forEach((sortOption) => {
+        const [key, order] = sortOption.split(':');
+        sortingCriteria.push((order === 'desc' ? '-' : '') + key);
+      });
+      sort = sortingCriteria.join(' ');
     }
+
     const limit = options.limit && parseInt(options.limit, 10) > 0 ? parseInt(options.limit, 10) : 10;
     const page = options.page && parseInt(options.page, 10) > 0 ? parseInt(options.page, 10) : 1;
     const skip = (page - 1) * limit;

tests/integration/user.test.js

@@ -219,7 +219,7 @@ describe('User routes', () => {
       expect(res.body.results[1].id).toBe(userTwo._id.toHexString());
     });
 
-    test('should correctly sort returned array if descending sort param is specified', async () => {
+    test('should correctly sort the returned array if descending sort param is specified', async () => {
       await insertUsers([userOne, userTwo, admin]);
 
       const res = await request(app)
@@ -242,7 +242,7 @@ describe('User routes', () => {
       expect(res.body.results[2].id).toBe(admin._id.toHexString());
     });
 
-    test('should correctly sort returned array if ascending sort param is specified', async () => {
+    test('should correctly sort the returned array if ascending sort param is specified', async () => {
       await insertUsers([userOne, userTwo, admin]);
 
       const res = await request(app)
@@ -265,6 +265,40 @@ describe('User routes', () => {
       expect(res.body.results[2].id).toBe(userTwo._id.toHexString());
     });
 
+    test('should correctly sort the returned array if multiple sorting criteria are specified', async () => {
+      await insertUsers([userOne, userTwo, admin]);
+
+      const res = await request(app)
+        .get('/v1/users')
+        .set('Authorization', `Bearer ${adminAccessToken}`)
+        .query({ sortBy: 'role:desc,name:asc' })
+        .send()
+        .expect(httpStatus.OK);
+
+      expect(res.body).toEqual({
+        results: expect.any(Array),
+        page: 1,
+        limit: 10,
+        totalPages: 1,
+        totalResults: 3,
+      });
+      expect(res.body.results).toHaveLength(3);
+
+      const expectedOrder = [userOne, userTwo, admin].sort((a, b) => {
+        if (a.role < b.role) {
+          return 1;
+        }
+        if (a.role > b.role) {
+          return -1;
+        }
+        return a.name < b.name ? -1 : 1;
+      });
+
+      expectedOrder.forEach((user, index) => {
+        expect(res.body.results[index].id).toBe(user._id.toHexString());
+      });
+    });
+
     test('should limit returned array if limit param is specified', async () => {
       await insertUsers([userOne, userTwo, admin]);