feat: support _is_null and _is_not_null operators

Author: zlargon

README.md

@@ -105,7 +105,7 @@ __Please help me build OSS__ 👉 [GitHub Sponsors](https://github.com/sponsors/
 
 ## Getting started
 
-Install JSON Server 
+Install JSON Server
 
 ```
 npm install -g json-server
@@ -142,7 +142,7 @@ Also when doing requests, it's good to know that:
 - If you make POST, PUT, PATCH or DELETE requests, changes will be automatically and safely saved to `db.json` using [lowdb](https://github.com/typicode/lowdb).
 - Your request body JSON should be object enclosed, just like the GET output. (for example `{"name": "Foobar"}`)
 - Id values are not mutable. Any `id` value in the body of your PUT or PATCH request will be ignored. Only a value set in a POST request will be respected, but only if not already taken.
-- A POST, PUT or PATCH request should include a `Content-Type: application/json` header to use the JSON in the request body. Otherwise it will return a 2XX status code, but without changes being made to the data. 
+- A POST, PUT or PATCH request should include a `Content-Type: application/json` header to use the JSON in the request body. Otherwise it will return a 2XX status code, but without changes being made to the data.
 
 ## Routes
 
@@ -239,6 +239,18 @@ Add `_like` to filter (RegExp supported)
 GET /posts?title_like=server
 ```
 
+Add `_is_null` for getting a null value
+
+```
+GET /todos?completeDate_is_null
+```
+
+Add `_is_not_null` for getting a non-null value
+
+```
+GET /todos?completeDate_is_not_null
+```
+
 ### Full-text search
 
 Add `q`

__tests__/server/plural.js

@@ -42,6 +42,13 @@ describe('Server', () => {
       { id: 5, body: 'quux', published: false, postId: 2, userId: 1 },
     ]
 
+    db.todos = [
+      { id: 1, completeDate: null },
+      { id: 2, completeDate: null },
+      { id: 3, completeDate: '2022-11-20T13:02:47.210Z' },
+      { id: 4, completeDate: '2023-12-05T17:58:17.420Z' },
+    ]
+
     db.buyers = [
       { id: 1, name: 'Aileen', country: 'Colombia', total: 100 },
       { id: 2, name: 'Barney', country: 'Colombia', total: 200 },
@@ -305,6 +312,22 @@ describe('Server', () => {
     })
   })
 
+  describe('GET /:resource?attr_is_null', () => {
+    test('should respond with null value array', () =>
+      request(server)
+        .get('/todos?completeDate_is_null')
+        .expect('Content-Type', /json/)
+        .expect(200, db.todos.slice(0, 2)))
+  })
+
+  describe('GET /:resource?attr_is_not_null', () => {
+    test('should respond with non-null value array', () =>
+      request(server)
+        .get('/todos?completeDate_is_not_null')
+        .expect('Content-Type', /json/)
+        .expect(200, db.todos.slice(2)))
+  })
+
   describe('GET /:resource?attr_gte=&attr_lte=', () => {
     test('should respond with a limited array', () =>
       request(server)

src/server/router/plural.js

@@ -81,6 +81,8 @@ module.exports = (db, name, opts) => {
           _.has(arr[i], query) ||
           query === 'callback' ||
           query === '_' ||
+          /_is_null$/.test(query) ||
+          /_is_not_null$/.test(query) ||
           /_lte$/.test(query) ||
           /_gte$/.test(query) ||
           /_ne$/.test(query) ||
@@ -117,22 +119,30 @@ module.exports = (db, name, opts) => {
         // Always use an array, in case req.query is an array
         const arr = [].concat(req.query[key])
 
+        const isNull = /_is_null$/.test(key)
+        const isNotNull = /_is_not_null$/.test(key)
         const isDifferent = /_ne$/.test(key)
         const isRange = /_lte$/.test(key) || /_gte$/.test(key)
         const isLike = /_like$/.test(key)
-        const path = key.replace(/(_lte|_gte|_ne|_like)$/, '')
+        const path = key.replace(
+          /(_is_null|_is_not_null|_lte|_gte|_ne|_like)$/,
+          '',
+        )
 
         chain = chain.filter((element) => {
           return arr
-            .map(function (value) {
+            .map((value) => {
               // get item value based on path
               // i.e post.title -> 'foo'
               const elementValue = _.get(element, path)
+              const isElementValueNull =
+                typeof elementValue === 'undefined' || elementValue === null
+
+              if (isNull) return isElementValueNull
+              if (isNotNull) return !isElementValueNull
 
               // Prevent toString() failing on undefined or null values
-              if (elementValue === undefined || elementValue === null) {
-                return undefined
-              }
+              if (isElementValueNull) return undefined
 
               if (isRange) {
                 const isLowerThan = /_gte$/.test(key)