节点异步函数返回'is not a function'

Question

我一直在遵循关于在Node中设置REST api的教程，使用Express为访问现有MariaDB数据库的应用程序。我的版本只需要读取数据，并且我有与Node应用程序(同一主机)共同定位的DB。

这个入门级示例的目标是使用静态SQL访问数据，因此我可以看到它通过JSON排序符呈现在网页中。

[接下来，我想在一个表(EJS?)中显示数据。稍后，当我可以让它工作时，我将添加表单控件(React?)，让用户为SQL查询指定开始和结束日期界限。最后，我的目标是将数据呈现为线形图(D3js)。

教程运行web服务器成功(它返回'OK'的基础URL)，但当我去到URL/solarData它尝试异步函数从数据库中获取多行，它响应solarData.getMultiple is not a function TypeError: solarData.getMultiple is not a function

。/app.js

const express = require('express');
const app = express();
const port = process.env.PORT || 3800;
const solarDataRouter = require('./routes/solarData');
app.use(express.json());
app.use(
express.urlencoded({
extended: true,
})
);
app.get('/', (req, res) => {
res.json({'message': 'ok'});
})
app.use('/solarData', solarDataRouter);
/* Error handler middleware */
app.use((err, req, res, next) => {
const statusCode = err.statusCode || 500;
console.error(err.message, err.stack);
res.status(statusCode).json({'message': err.message});

return;
});
app.listen(port, () => {
console.log(`Example app listening at http://localhost:${port}`)
});

。/线路/solarData.js

const express = require('express');
const router = express.Router();
const solarData = require('../services/solarData');
/* GET solar data. */
router.get('/', async function(req, res, next) {
try {
res.json(await solarData.getMultiple(req.query.page));
} catch (err) {
console.error(`Error while getting solar data `, err.message);
next(err);
}
});
module.exports = router;

。/config.js

const env = process.env;
const config = {
db: { 
host: env.SUNNY_HOST,
user: env.SUNNY_USER,
password: env.SUNNY_PW,
database: env.SUNNY_DB,
},
listPerPage: env.LIST_PER_PAGE,
};
module.exports = config;

。/服务/solarData.js

const db = require('./db');
const helper = require('../helper');
const config = require('../config');
async function getMultiple(page = 1){
const offset = helper.getOffset(page, config.listPerPage);
const rows = await db.query(
`SELECT idxDTP, year(DT) AS Year, month(DT) AS Month, day(DT) AS Day, hour(DT) AS Hour, minute(DT) AS Min, PWR AS Power FROM DTP WHERE (DT >= '2021-01-12 12:30:00') AND (DT <= '2021-01-12 12:40:00') ORDER BY Year ASC, Month ASC, Day ASC, Hour ASC, Min ASC LIMIT ?,?`, 
[offset, config.listPerPage]
);
const data = helper.emptyOrRows(rows);
const meta = {page};
return {
data,
meta
}
}

。/服务/db.js

const mysql = require('mysql2/promise');
const config = require('../config');
async function query(sql, params) {
const connection = await mysql.createConnection(config.db);
const [results, ] = await connection.execute(sql, params);
return results;
}
module.exports = {
query
}

我省略了。/helper.js

一切运行正常，直到我把网页指向/solarData。在这一点上，我得到:<<strong>调试控制台/strong>(vscode)

/Error while getting solar data  solarData.getMultiple is not a function
routes/solarData.js:10
solarData.getMultiple is not a function TypeError: solarData.getMultiple is not a function
at /SunnyData/solarViz/routes/solarData.js:8:30
at Layer.handle [as handle_request] (/SunnyData/solarViz/node_modules/express/lib/router/layer.js:95:5)
at next (/SunnyData/solarViz/node_modules/express/lib/router/route.js:137:13)
at Route.dispatch (/SunnyData/solarViz/node_modules/express/lib/router/route.js:112:3)
at Layer.handle [as handle_request] (/SunnyData/solarViz/node_modules/express/lib/router/layer.js:95:5)
at /SunnyData/solarViz/node_modules/express/lib/router/index.js:281:22
at Function.process_params (/SunnyData/solarViz/node_modules/express/lib/router/index.js:335:12)
at next (/SunnyData/solarViz/node_modules/express/lib/router/index.js:275:10)
at Function.handle (/SunnyData/solarViz/node_modules/express/lib/router/index.js:174:3)
at router (/SunnyData/solarViz/node_modules/express/lib/router/index.js:47:12)

毫无疑问，这是一个简单的问题，但我找不到现有的问题，以一种我能理解的方式涵盖这个场景(我是Node/Express等的新手)

希望我已经把足够的信息。如果我还需要补充什么，请告诉我。

Answer 1

你应该在./services/solarData.js下面一行导出函数;

module.exports.getMultiple = getMultiple;

它将允许Node.js导出该函数并在其他文件中需要它