Feature/add preserve default nullable (#50)

* feat: add preserveDefaultNullable setting

* docs: document preserveDefaultNullable field

README.md

@@ -262,6 +262,8 @@ export class ProductDto extends IntersectionType(
     -   set prisma client import path manually, default value is **@prisma/client**
 -   _useNonNullableAssertions_
     -   Apply a ! after non-optional class fields to avoid strict mode warnings (Property has no initializer and is not definitely assigned in the constructor.)
+-   _preserveDefaultNullable_
+    -   Determines how null fields are handled. When set to **false** (default), it turns all null fields to undefined. Otherwise, it follows Prisma generation and adds null to the type.
 
 ### **How it works?**
 

src/components/field.component.ts

@@ -5,15 +5,21 @@ import { BaseComponent } from './base.component'
 export class FieldComponent extends BaseComponent implements Echoable {
 	name: string
 	nonNullableAssertion: boolean
+	preserveDefaultNullable: boolean
 	nullable: boolean
 	useUndefinedDefault: boolean
 	default?: string
 	type?: string
 
 	echo = () => {
 		let name = this.name
+		let type = this.type
 		if (this.nullable === true) {
-			name += '?'
+			if (this.preserveDefaultNullable) {
+				type = this.type + ' | null'
+			} else {
+				name += '?'
+			}
 		} else if (this.nonNullableAssertion === true) {
 			name += '!'
 		}
@@ -29,7 +35,7 @@ export class FieldComponent extends BaseComponent implements Echoable {
 
 		return FIELD_TEMPLATE.replace('#!{NAME}', name)
 			.replace('#!{NAME}', name)
-			.replace('#!{TYPE}', this.type)
+			.replace('#!{TYPE}', type)
 			.replace('#!{DECORATORS}', this.echoDecorators())
 			.replace('#!{DEFAULT}', defaultValue)
 	}

src/convertor.ts

@@ -354,6 +354,10 @@ export class PrismaConvertor {
 			field.nonNullableAssertion = true
 		}
 
+		if(this.config.preserveDefaultNullable) {
+			field.preserveDefaultNullable = true
+		}
+
 		if (dmmfField.default) {
 			if (typeof dmmfField.default !== 'object') {
 				field.default = dmmfField.default?.toString()

src/generator.ts

@@ -49,6 +49,10 @@ export const PrismaClassGeneratorOptions = {
 	useNonNullableAssertions: {
 		desc: 'applies non-nullable assertions (!) to class properties',
 		defaultValue: false
+	},
+	preserveDefaultNullable: {
+		defaultValue: false,
+		desc: 'preserve default nullable behavior'
 	}
 } as const