Angular 2第一次服务调用.subscribe（）失败并显示“连接已关闭”

Question

第一个失败而第二个失败。

this.doelplatformService.getAllDoelplatformen()
  .subscribe(
  doelplatformData => this.doelplatformGridOptions.api.setDatasource(doelplatformData));

this.userService.getAllUsers()
  .subscribe(
  userData => this.userGridOptions.api.setRowData(userData));

这是错误：

{ ConnectionError: Connection is closed.
at C:\Users\myname\Documents\Octopus\Octopus 2.0\node_modules\mssql\lib\main.js:1569:17
at _combinedTickCallback (internal/process/next_tick.js:67:7)
at process._tickCallback (internal/process/next_tick.js:98:9)
name: 'ConnectionError',
message: 'Connection is closed.',
code: 'ECONNCLOSED' }
(node:7376) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): ConnectionError: Connection is closed.

我做错了什么，我该如何解决？ 提前谢谢！

修改

以下是getAllDoelplatformen（）函数的代码

getAllDoelplatformen() {
return this.http.get('/api/doelplatformen')
  .map(res => res.json());
}

它指向这个api：

const express = require('express');
const router = express.Router();

var sql = require("mssql");

var dbconfig = {
server: "**********",
user: "**********",
password: "***********",
options: {
    database: "*********"
}
};

// Get all doelplatformen
router.get('/doelplatformen', (req, res) => {
sql.connect(dbconfig, function (err) {
    var request = new sql.Request();
    if (err) {
        console.log(err);
        return;
    }
    request.query("SELECT [Alg].[DefTarget].[ShortName] Platform, [Alg].[DefTarget].[ID] FROM [Alg].[DefTarget];", function (err, recordset) {
        if (err) {
            console.log(err);
            return;
        }
        else {
            res.end(JSON.stringify(recordset));
        }
    });
    request.query();
});
});