inheritance support (#7)

* use prototype chain for searching fields

.eslintrc.js

@@ -1,4 +1,5 @@
 module.exports = {
+  root: true,
   parser: '@typescript-eslint/parser',  // Specifies the ESLint parser
   plugins: ["@typescript-eslint"],
   extends: [

README.md

@@ -7,6 +7,8 @@ This lib provide decorator for fixed width file so that the domain class and spe
 ## Example
 This lib uses [reflect-metadata](https://github.com/rbuckton/reflect-metadata) for Meta programming.
 
+Inheritance is supported that fields decorated in parent classes will also be included/processed.
+
 ### Model definition
 
 ```typescript
@@ -17,7 +19,7 @@ export class Transaction extends FixedWidthConvertible {
 
   @FixedWidth({ start: 5, width: 40 })
   parentName: string;
-  
+
   @FixedWidth({ start: 45, width: 40, format: { type: DataType.Float } })
   taxAmount: number;
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fixed-width-ts-decorator",
-  "version": "1.1.0",
+  "version": "1.2.0",
   "description": "Fixed width file handler with TypeScript Decorator",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

src/fixed-width-convertible.ts

@@ -6,7 +6,7 @@ export abstract class FixedWidthConvertible {
   }
 
   static convertFixedWidth<T extends Record<string, any>>(line: string, target: T): T {
-    const fields = Reflect.getMetadata(fixedWidthVariableKey, target.constructor, fixedWidthVariableKey);
+    const fields = this.getAllFields(target.constructor);
     for (const field of fields) {
       const options: FixedWidthOptions = Reflect.getMetadata(fixedWidthMetadataKey, target, field);
       const value = line.substring(options.start, options.start + options.width).trim();
@@ -21,5 +21,17 @@ export abstract class FixedWidthConvertible {
     }
     return target;
   }
+
+  /**
+   * @param clz the class/constructor
+   * @returns the fields decorated with @FixedWidth all the way up the prototype chain.
+   */
+  static getAllFields(clz: Record<string, any>): string[] {
+    if(!clz) return [];
+    const fields: string[] | undefined = Reflect.getMetadata(fixedWidthVariableKey, clz, fixedWidthVariableKey);
+    // get `__proto__` and (recursively) all parent classes
+    const rs = new Set([...(fields || []), ...this.getAllFields(Object.getPrototypeOf(clz))]);
+    return Array.from(rs);
+  }
 }
 

src/fixed-width-decorator.test.ts

@@ -1,5 +1,6 @@
 import fs from 'fs';
 import { FixedWidthConvertible } from './fixed-width-convertible';
+import { ChildTransaction } from './scripts/ChildTransaction';
 import { Transaction } from './scripts/Transaction';
 
 describe('fixed width file test', () => {
@@ -35,5 +36,22 @@ describe('fixed width file test', () => {
     expect(rs[1].taxAmount).toBe(123.45);
     expect(rs[2].taxAmount).toBe(12.35);
     expect(rs[0].clientId).toBe('20000');
+    // should not have child class field
+    expect((rs[0] as any).paymentId).toBeUndefined();
   });
+
+  test('should get Field from parent class', () => {
+    const rs: Array<ChildTransaction> = lines.map(line => {
+      const trans = new ChildTransaction();
+      FixedWidthConvertible.convertFixedWidth(line, trans);
+      return trans;
+    });
+    expect(rs.length).toBe(4);
+    // should have parent class fields
+    expect(rs[1].taxAmount).toBe(123.45);
+    expect(rs[2].taxAmount).toBe(12.35);
+    expect(rs[0].clientId).toBe('20000');
+    expect(rs[0].paymentId).not.toBeUndefined();
+  });
+
 });

src/scripts/ChildTransaction.ts

@@ -0,0 +1,7 @@
+import { FixedWidth } from '../fixed-width-decorator';
+import { Transaction } from './Transaction';
+
+export class ChildTransaction extends Transaction {
+  @FixedWidth({ start: 225, width: 40 })
+  paymentId: string;
+}

src/scripts/Transaction.ts

@@ -7,7 +7,7 @@ export class Transaction extends FixedWidthConvertible {
 
   @FixedWidth({ start: 5, width: 40 })
   parentName: string;
-  
+
   @FixedWidth({ start: 45, width: 40, format: { type: DataType.Float } })
   taxAmount: number;
 
@@ -31,8 +31,6 @@ export class Transaction extends FixedWidthConvertible {
   @FixedWidth({ start: 145, width: 40 })
   userId: string;
 
-  @FixedWidth({ start: 225, width: 40 })
-  paymentId: string;
   // other non-decorated fields
   otherField: string;
 }

src/scripts/trigger.ts

@@ -1,12 +1,13 @@
 import 'reflect-metadata';
 import fs from 'fs';
 import { Transaction } from './Transaction';
+import { ChildTransaction } from './ChildTransaction';
 
 (() => {
   const file = fs.readFileSync('data/sample.txt', { encoding: 'utf8' });
   const lines = file.split('\n').filter(l => l);
   const rs: Array<Transaction> = lines.map(line => {
-    const trans = new Transaction();
+    const trans = new ChildTransaction();
     trans.convertFixedWidth(line);
     // FixedWidthConvertible.convertFixedWidth(line, trans);
     return trans;