本系列文章我们将介绍如何为 SAP S4HANA Cloud 系统开发扩展程序 （Extension App）。在做 SAP （以及 Microsoft, Salesforce 等 ERP）产品时少不了面对 OData Service，那么对于 Node.js 程序怎么样开发 OData 服务呐？本文（项目源代码可下载自 GitLab sourcecode）将介绍使用 odata-v4-server 这个组件来开发 OData 服务。
Step 1. Setup OData v4 Server Module
在 app 文件夹内安装 odata-v4-server dependencies ：
npm install odata-v4-server --save
因为 odata-v4-server 会使用到 decorator 语法，所以我们需要更新 TypeScript 配置文件 tsconfig.json 去支持此语法
{
"compilerOptions": {
...
"emitDecoratorMetadata": true,
"experimentalDecorators": true
},
...
}
Node.js 10 已经 Native 支持大部分 ES6 标准语法了，所以我们把编译 target 改成 es6
"compilerOptions": {
/* Basic Options */
"target": "es6"
}
后面会遇到编译错误:
node_modules/odata-v4-server/build/lib/processor.d.ts:21:22 - error TS2415: Class 'ODataProcessor' incorrectly extends base class 'Transform'.
Property '_flush' is protected in type 'ODataProcessor' but public in type 'Transform'.
21 export declare class ODataProcessor extends Transform {
~~~~~~~~~~~~~~
这个的意思是 ODataProcessor 类的 _flush 不该声明为 protected 而应该是父类 Transform 里的此方法的 public ，不能比父类访问范围小。似乎暂时联系不上此包作者，所以暂时可以用脚本修改这个代码，或者 fork 出来修改项目。脚本修改，在 package.json 里加入
"scripts": {
"postinstall": "sh scripts/postinstall.sh",
...
},
新建脚本文件 scripts/postinstall.sh 内容为
set -e
set -x
sed -i.bak 's/protected _flush/public _flush/' node_modules/odata-v4-server/build/lib/processor.d.ts
Step 2. Coding OData
Data Interfaces
新建文件 src/BusinessPartner.ts
export interface BusinessPartner {
_id?: number;
firstName?: string;
lastName?: string;
fullName?: string;
}
const businessPartners = [
{
_id: 1,
firstName: "Tiven",
lastName: "Wang",
fullName: "Tiven Wang"
},
{
_id: 2,
firstName: "Elon",
lastName: "Musk",
fullName: "Elon Musk"
}
] as BusinessPartner[];
var lastId = 2;
export const findBusinessPartners = () =>
new Promise<BusinessPartner[]>(resolve => {
resolve(businessPartners);
});
export const findOneBusinessPartner = (id: number) =>
new Promise<BusinessPartner>((resolve, reject) => {
const bp = businessPartners.find(element => element._id === id);
if (bp === undefined) {
reject();
}
resolve(bp);
});
export const insertBusinessPartner = ({ firstName = '', lastName = '' }: BusinessPartner) =>
new Promise<BusinessPartner>(resolve => {
lastId += 1;
const bp = {
_id: lastId,
firstName,
lastName,
fullName: firstName + " " + lastName
};
businessPartners.push(bp);
resolve(bp);
});
export const updateBusinessPartner = (id: number, { firstName, lastName }: BusinessPartner) =>
new Promise((resolve, reject) => {
const index = businessPartners.findIndex(element => element._id === id);
if (index === -1) {
reject();
return;
}
const prevBP = businessPartners[index];
const bp = {
_id: prevBP._id,
firstName: firstName !== undefined ? firstName : prevBP.firstName,
lastName: lastName !== undefined ? lastName : prevBP.lastName,
fullName: firstName + " " + lastName,
};
businessPartners[index] = bp;
resolve();
});
export const deleteBusinessPartner = (id: number) =>
new Promise((resolve, reject) => {
const index = businessPartners.findIndex(element => element._id === id);
if (index === -1) {
reject();
return;
}
businessPartners.splice(index, 1);
resolve();
});
这个代码实现了一个实体 BusinessPartner 和其相应的 CRUD 操作函数，为了简单起见没有使用数据库持久化存储数据，而是直接使用了个数组，后续我们会介绍使用数据库服务做持久化等操作。
因为真实使用数据库时 CRUD 一般会是异步操作，所以这里我们使用 Promises 来模拟异步功能。
OData Service Implementation
Models
创建 OData 的 Models ，文件为 src/MyODataServer/models/BusinessPartner.ts
import { Edm } from 'odata-v4-server';
import { BusinessPartner as IBP } from '../../BusinessPartner'
export default class BusinessPartner implements IBP {
@Edm.Key
@Edm.Int32
public _id?: number;
@Edm.String
public firstName?: string;
@Edm.String
public lastName?: string;
@Edm.String
public fullName?: string;
}
此类就代表了 OData 里的 Entity BusinessPartner
Controller
创建 Controller 文件 src/MyODataServer/controllers/BusinessPartnersController.ts
import { odata, ODataController } from 'odata-v4-server';
import { deleteBusinessPartner, findOneBusinessPartner, findBusinessPartners, insertBusinessPartner, updateBusinessPartner } from '../../BusinessPartner';
import BusinessPartner from '../models/BusinessPartner';
@odata.type(BusinessPartner)
export default class BusinessPartnersController extends ODataController {
@odata.GET
public async find(): Promise<BusinessPartner[]> {
const bps = await findBusinessPartners();
return bps;
}
@odata.GET
public async findOne(@odata.key id: number): Promise<BusinessPartner> {
const bps = await findOneBusinessPartner(id);
return bps;
}
@odata.POST
public async insert(@odata.body body: any): Promise<BusinessPartner> {
// BUG: CANNOT BE EMPTY OBJECT
const bps = await insertBusinessPartner(body);
return bps;
}
@odata.PATCH
public async update(@odata.key id: number, @odata.body body: any) {
// BUG: CANNOT BE EMPTY OBJECT
await updateBusinessPartner(id, body);
}
@odata.DELETE
public async remove(@odata.key id: number) {
await deleteBusinessPartner(id);
}
}
此 Controller 继承了 ODataController 实现了基本的 HTTP Operators，调用了模拟访问数据库读写数据的操作
Module Export
最后定义一个文件夹或者叫 Module 的默认输出，文件为 src/MyODataServer/index.ts
import { odata, ODataServer } from 'odata-v4-server';
import BusinessPartnersController from './controllers/BusinessPartnerController';
@odata.namespace('My')
@odata.controller(BusinessPartnersController, true)
export default class MyODataServer extends ODataServer {}
Step 3. Routing
最后把我们的 OData Server 添加到 Express 路由里发布出去
...
import MyODataServer from './MyODataServer';
...
app.use('/odata', MyODataServer.create());
app.listen(appEnv.port || port, appEnv.bind, () => {
console.log("Express server listening on port " + appEnv.url);
});
export default app;
Step 4. Testing
运行命令启动应用 npm run start:local, 然后访问链接 *
Wrap Up
对于这种个人开发的程序包使用起来感受确实不好。建议如果是 SAP 产品开发要用 OData 服务还是考虑使用 SAP Cloud Foundry XSA 去开发。
Comments