feat(repository): add null type

packages/repository/src/__tests__/unit/type/type.unit.ts

@@ -349,6 +349,45 @@ describe('types', () => {
     });
   });
 
+  describe('null', () => {
+    const nullType = new types.NullType();
+    it('checks isInstance', () => {
+      expect(nullType.isInstance('str')).to.be.false();
+      expect(nullType.isInstance(null)).to.be.true();
+      expect(nullType.isInstance(undefined)).to.be.false();
+      expect(nullType.isInstance(true)).to.be.false();
+      expect(nullType.isInstance(false)).to.be.false();
+      expect(nullType.isInstance({x: 1})).to.be.false();
+      expect(nullType.isInstance([1, 2])).to.be.false();
+      expect(nullType.isInstance(1)).to.be.false();
+      expect(nullType.isInstance(new Date())).to.be.false();
+    });
+
+    it('checks isCoercible', () => {
+      expect(nullType.isCoercible('str')).to.be.false();
+      expect(nullType.isCoercible(null)).to.be.true();
+      expect(nullType.isCoercible(undefined)).to.be.true();
+      expect(nullType.isCoercible(true)).to.be.false();
+      expect(nullType.isCoercible({x: 1})).to.be.false();
+      expect(nullType.isCoercible(1)).to.be.false();
+      expect(nullType.isCoercible(new Date())).to.be.false();
+    });
+
+    it('creates defaultValue', () => {
+      expect(nullType.defaultValue()).to.be.null();
+    });
+
+    it('coerces values', () => {
+      expect(nullType.coerce(null)).to.null();
+      expect(nullType.coerce(undefined)).to.null();
+    });
+
+    it('serializes values', () => {
+      expect(nullType.serialize(null)).null();
+      expect(nullType.serialize(undefined)).null();
+    });
+  });
+
   describe('array', () => {
     const stringType = new types.StringType();
     const arrayType = new types.ArrayType(stringType);

packages/repository/src/type-resolver.ts

@@ -51,6 +51,13 @@ export function isTypeResolver<T extends object>(
   return true;
 }
 
+/**
+ * A boxed type for `null`
+ */
+export function Null() {
+  return null;
+}
+
 /**
  * Check if the provided function is a built-in type provided by JavaScript
  * and/or Node.js. E.g. `Number`, `Array`, `Buffer`, etc.
@@ -67,6 +74,7 @@ export function isBuiltinType(fn: Function): boolean {
     fn === Date ||
     fn === RegExp ||
     fn === Buffer ||
+    fn === Null ||
     // function as a type
     fn === Function
   );

packages/repository/src/types/index.ts

@@ -15,17 +15,18 @@
  * - ArrayType: Array<T>
  * - UnionType: Union of types
  */
-import {Type} from './type';
-import {StringType} from './string';
-import {BooleanType} from './boolean';
-import {NumberType} from './number';
-import {DateType} from './date';
-import {BufferType} from './buffer';
 import {AnyType} from './any';
 import {ArrayType} from './array';
-import {UnionType} from './union';
-import {ObjectType} from './object';
+import {BooleanType} from './boolean';
+import {BufferType} from './buffer';
+import {DateType} from './date';
 import {ModelType} from './model';
+import {NullType} from './null';
+import {NumberType} from './number';
+import {ObjectType} from './object';
+import {StringType} from './string';
+import {Type} from './type';
+import {UnionType} from './union';
 
 export {
   Type,
@@ -38,6 +39,7 @@ export {
   ArrayType,
   UnionType,
   ModelType,
+  NullType,
   ObjectType,
 };
 
@@ -47,3 +49,4 @@ export const NUMBER = new NumberType();
 export const DATE = new DateType();
 export const BUFFER = new BufferType();
 export const ANY = new AnyType();
+export const NULL = new NullType();

packages/repository/src/types/null.ts

@@ -0,0 +1,35 @@
+// Copyright IBM Corp. 2017,2019. All Rights Reserved.
+// Node module: @loopback/repository
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+import {Type} from './type';
+
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
+/**
+ * Null type
+ */
+export class NullType implements Type<null> {
+  readonly name = 'boolean';
+
+  isInstance(value: any) {
+    return value === null;
+  }
+
+  defaultValue() {
+    return null;
+  }
+
+  isCoercible(value: any): boolean {
+    return value == null;
+  }
+
+  coerce(value: any) {
+    return null;
+  }
+
+  serialize(value: boolean | null | undefined) {
+    return null;
+  }
+}