From 081177aebfe548cf0ad75a77aafe109aab62112a Mon Sep 17 00:00:00 2001
From: Elbarae Rguig <elbarae1921@gmail.com>
Date: Sat, 20 Aug 2022 23:25:48 +0100
Subject: [PATCH] feat: add ability to specify whether null values should be
 put at the beginning or the end of the result set when sorting (#296)

---
 README.md            |  8 ++++++++
 src/paginate.spec.ts | 16 ++++++++++++++++
 src/paginate.ts      |  7 +++++--
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 4053b8b..42ff434 100644
--- a/README.md
+++ b/README.md
@@ -124,6 +124,7 @@ export class CatsService {
   public findAll(query: PaginateQuery): Promise<Paginated<CatEntity>> {
     return paginate(query, this.catsRepository, {
       sortableColumns: ['id', 'name', 'color', 'age'],
+      nullSort: 'last',
       searchableColumns: ['name', 'color', 'age'],
       defaultSortBy: [['id', 'DESC']],
       filterableColumns: {
@@ -154,6 +155,13 @@ const paginateConfig: PaginateConfig<CatEntity> {
    * Description: These are the columns that are valid to be sorted by.
    */
   sortableColumns: ['id', 'name', 'color'],
+  /**
+   * Required: false
+   * Type: 'first' | 'last'
+   * Default: 'last'
+   * Description: Define whether to put null values at the beginning or end of the result set.
+   */
+  nullSort: 'last,
 
   /**
    * Required: false
diff --git a/src/paginate.spec.ts b/src/paginate.spec.ts
index 4a30671..65cf44e 100644
--- a/src/paginate.spec.ts
+++ b/src/paginate.spec.ts
@@ -196,6 +196,22 @@ describe('paginate', () => {
         expect(result.data).toStrictEqual(cats.slice(0).reverse())
     })
 
+    it('should put null values last when sorting', async () => {
+        const config: PaginateConfig<CatEntity> = {
+            sortableColumns: ['age', 'createdAt'],
+            nullSort: 'last',
+            defaultSortBy: [['age', 'DESC']],
+        }
+        const query: PaginateQuery = {
+            path: '',
+        }
+
+        const result = await paginate<CatEntity>(query, catRepo, config)
+
+        expect(result.meta.sortBy).toStrictEqual([['age', 'DESC']])
+        expect(result.data).toStrictEqual(cats)
+    })
+
     it('should sort result by multiple columns', async () => {
         const config: PaginateConfig<CatEntity> = {
             sortableColumns: ['name', 'color'],
diff --git a/src/paginate.ts b/src/paginate.ts
index 4bcbf91..e15b16d 100644
--- a/src/paginate.ts
+++ b/src/paginate.ts
@@ -46,6 +46,7 @@ export class Paginated<T> {
 export interface PaginateConfig<T> {
     relations?: RelationColumn<T>[]
     sortableColumns: Column<T>[]
+    nullSort?: 'first' | 'last'
     searchableColumns?: Column<T>[]
     select?: Column<T>[]
     maxLimit?: number
@@ -172,6 +173,8 @@ export async function paginate<T>(
 
     if (config.sortableColumns.length < 1) throw new ServiceUnavailableException()
 
+    const NULL_SORT = config.nullSort === 'last' ? 'NULLS LAST' : 'NULLS FIRST'
+
     if (query.sortBy) {
         for (const order of query.sortBy) {
             if (isEntityKey(config.sortableColumns, order[0]) && ['ASC', 'DESC'].includes(order[1])) {
@@ -219,9 +222,9 @@ export async function paginate<T>(
 
     for (const order of sortBy) {
         if (order[0].split('.').length > 1) {
-            queryBuilder.addOrderBy(`${queryBuilder.alias}_${order[0]}`, order[1])
+            queryBuilder.addOrderBy(`${queryBuilder.alias}_${order[0]}`, order[1], NULL_SORT)
         } else {
-            queryBuilder.addOrderBy(`${queryBuilder.alias}.${order[0]}`, order[1])
+            queryBuilder.addOrderBy(`${queryBuilder.alias}.${order[0]}`, order[1], NULL_SORT)
         }
     }