How to handle Promise in nodejs - mysql

Question

I'm trying to execute a callback function in nodejs, using expressjs and angular 2 (i don't know if the angular2 part it's relevant).
What I do is:
I have a formular in angular2, with that I send a get request to my API route, then I send the text field in the formular to the URL via get, then I do an MYSQL query to look into a phonebook database, and I'm expecting to get a complete user with his details, from the phonebook.
Formular:
<div class="container">
<div class="col-md-4">
<h1>Addressbook</h1>
<form [formGroup]="searchForm" (ngSubmit)="doSearch($event)">
<input formControlName="searchString" type="text" placeholder="Name">
<button type="submit">Search</button>
</form>
</div>
</div>
First function, doSearch:
doSearch(event) {
let formData = this.searchForm.value;
var searchString = this.searchForm.value.searchString;
this.http.get('/phonebook/search/'+searchString, function(req, res){}).subscribe(
function(response) {
console.log("Success Response");
},
function(error) { console.log("Error happened" + error)},
function() { console.log("the subscription is completed")}
);
}
This calls to the route sending a parameter, so not so hard.
Now the create router gets into the game:
public static create(router: Router, basePath: string) {
console.log("[SearchRoute::create] Creating routes for /search.");
// call the function for retrieving the address book results
router.get(basePath + "/search/:searchString", (req: Request, res: Response, next: NextFunction) => {
console.log("## [SearchRoute] Called GET /search.");
var object = searchUser(req);
console.log(object);
});
}
And finally, the function searchUser gets called:
function searchUser(req: Request) {
console.log("searchUser Function executed.");
var searchString = req.params.searchString;
var query = p_query('SELECT XXXX')
.then(function (results) {
console.log("query executed and all okay");
return (results);
})
.catch(function (error) {
console.error("Wooopsi", error);
});
console.log("query result: "+query);
}
Additionally, I post here the new query function that I build to be able to handle promises (which I don't know if it was the best choice):
function p_query(q) {
return new Promise(function (resolve, reject) {
// The Promise constructor should catch any errors thrown on
// this tick. Alternately, try/catch and reject(err) on catch.
myMYSQL.db.query(
q,
function (error, results) {
if (error)
reject(error);
resolve(results);
});
})
};
So, what I actually want to do, what's my issue?
I want to send the result of the query back to the client (the angular2 formular), and I was not being able to do it...
So after this really long post, I really appreciate if you read til here, and sorry for the complicated question!
PS: I know i explain myself really bad :(
Regards,
Daniel

Answer 1

In this official angular 2 documentation on the http client they propose to put the http logic into a separate service. I've setup it similar to the example just for a search.service.ts:
import { Injectable } from '#angular/core';
import { Http, Response,Headers, RequestOptions,URLSearchParams }
from '#angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/map';
#Injectable()
export class SearchService {
constructor(private http: Http) {
}
getSearchResult(searchString) : Observable<any> {
return this.http.get('/phonebook/search/'+searchString)
.map(this.extractData)
.catch(this.handleError);
}
private extractData(res: Response) {
let body = res.json();
return body;
}
private handleError (error: Response | any) {
let errMsg: string;
if (error instanceof Response) {
const body = error.json() || '';
const err = body.error || JSON.stringify(body);
errMsg = `${error.status} - ${error.statusText || ''} ${err}`;
} else {
errMsg = error.message ? error.message : error.toString();
}
return Observable.throw(errMsg);
}
}
In your component import the service and do the code snippets:
// don't forget to put the service in the app.modul or the component providers!
constructur(public mySearchService : SearchService) {}
// in your doSearch of your component:
doSearch(event) {
let formData = this.searchForm.value;
var searchString = this.searchForm.value.searchString;
mySearchService.getSearchResult(searchString).subscribe(
data => mylist.data, // or which datastructure I want to write to.
error => console.error(error) // or how I log the errors..
);
}
EDIT: The search_user in your database model:
function searchUser(searchString) {
console.log("searchUser Function executed.");
return myMYSQL.db.select('phonebookentry', {
pbe_lastname: searchString, pbe_syncstate: 'new'
}) // returning the promise/observable to the main function...
} // Currently I don't know, how the returned data looks like.
On the node/express side in the router send it with res.json EDIT: use asynchronous call to searchUser:
router.get(basePath + "/search/:searchString",
(req: Request, res: Response, next: NextFunction) => {
console.log("## [SearchRoute] Called GET /search.");
searchUser(req)
.then( data => res.json(data);console.log(data) )
.catch (error => console.log(error));
});

Answer 2

You should go with recursive callback with each query results try to enjoy the beauty of async platform.
Send data to client via
res.send(data);

Answer 3

Your answer it's completely perfect, i understand everything! The only problem that i'm facing now, its this one:
I'm calling the function searchUser, and it doesn't return anything, just an undefined object, so i quess i'm not doing the return correctly.
That's my searchUser function:
function searchUser(searchString) {
console.log("searchUser Function executed.");
myMYSQL.db.select('phonebookentry', {
pbe_lastname: searchString,
pbe_syncstate: 'new'
}).then(function (user) {
console.log("user before: "+user);
return (user);
}).catch(function (err) {
console.log(err);
})}
Thank you so much for your useful answer! I'm almost finished here