I'm following the tutorial. In Asynchronous hooks, there's a snippet like this:
todoService.before({
find(hook) {
return this.find().then(data => {
hook.params.message = 'Ran through promise hook';
hook.data.result = data;
// Always return the hook object
return hook;
});
}
});
Would you please let me know what this.find() is supposed to do?
find is a Feathers service method and this is the service the hook is running on.
Related
i want to make a method in my class. This method should connect to a MySQL database. I created my SQL code. And now I don't want to do a callback because this is old, I want to start using promises.
My function with callback (old school):
public does_player_exist(username: string, callback: any) {
this.mysql.connect();
this.mysql.query('USE devdb');
this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'"', (err: Error, result: any[]) {
if (result.length === 1) {
callback(true)
} else {
callback(false);
}
});
}
And here follows the method I tried to make a promise, but I failed:
public does_player_exist(username: string): Promise<boolean> {
this.mysql.connect();
this.mysql.query('USE devdb');
return this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'").toPromise().then((result) => {
return result.length === 1;
})
}
When I call this method:
service.does_player_exist('test').then((result) => { console.log(result) })
I hope someone can help me. Because I really don't want to be old school forever xD
Thanks in advance.
create a new Promise and resolve it / reject it in the callback functions of query. then return the promise. now does_player_exist returns a Promise object which contains for example then function
public does_player_exist(username: string, callback: any): Promise<boolean> {
this.mysql.connect();
this.mysql.query('USE devdb');
var promise = new Promise<boolean>();
this.mysql.query('SELECT p_name FROM players WHERE p_name = "'+username+'"', (err: Error, result: any[]) {
if (!err) promise.resolve(!!result.length);
else promise.reject();
});
return promise;
}
you will have to make sure that you have a Promise class available. that depends on your environment.
please be aware that without sanitizing your input (username) your application will be vulnerable and attackers could hijack your app.
Tip #1. Please use some kind of factory function to build your connection and reuse it later on.
Tip #2. Use prepared statement to prevent SQL injection.
Tip #3. Please use some promise library for that like Bluebird or Q. Most of the 3rd party promise libraries have a lot of useful utility methods to work with promises on of them is promisify. Promisify can wrap any nodejs type callback function into function which returns a promise.
Your example would look like:
// it's not a factory function*
public query() {
this.mysql.connect();
this.mysql.query('USE devdb');
return Promise.promisify(this.mysql.query.bind(this.mysql))
}
public does_player_exist(username: string): Promise<boolean> {
return this
.query('SELECT p_name FROM players WHERE p_name = ?', [username])
.then(result => result.length === 1);
}
I wrote a simple npm package to do this in a way that retains type-safety:
ts-promisify-callback
It requires you use typescript#^4.0 (upcoming release) and currently only works for callbacks in the popular format of (err, result) => {}.
I know this has something to do with using $q and promises, but I've been at it for hours and still can't quite figure out how it's supposed to work with my example.
I have a .json file with the data I want. I have a list of people with id's. I want to have a service or factory I can query with a parameter that'll http.get a json file I have, filter it based on the param, then send it back to my controller.
angular
.module("mainApp")
.controller('personInfoCtrl',['$scope', '$stateParams', 'GetPersonData', function($scope, $stateParams, GetPersonData) {
$scope.personId = $stateParams.id; //this part work great
$scope.fullObject = GetPersonData($stateParams.id);
//I'm having trouble getting ^^^ to work.
//I'm able to do
//GetPersonData($stateParams.id).success(function(data)
// { $scope.fullObject = data; });
//and I can filter it inside of that object, but I want to filter it in the factory/service
}]);
Inside my main.js I have
//angular.module(...
//..a bunch of urlrouterprovider and stateprovider stuff that works
//
}]).service('GetPersonData', ['$http', function($http)
{
return function(id) {
return $http.get('./data/people.json').then(function(res) {
//I know the problem lies in it not 'waiting' for the data to get back
//before it returns an empty json (or empty something or other)
return res.data.filter(function(el) { return el.id == id)
});
}
}]);
The syntax of the filtering and everything works great when it's all in the controller, but I want to use the same code in several controls, so I'm trying to break it out to a service (or factory, I just want the controllers to be 'clean' looking).
I'm really wanting to be able to inject "GetPersonData" to a controller, then call GetPersonData(personId) to get back the json
You seems to be syntax issue in your filter function in the service.
.service('GetPersonData', ['$http', function($http){
return function(id) {
return $http.get('./data/people.json').then( function (res) {
return res.data.filter(function(el) { return el.id == id });
});
}}]);
But regarding the original issue you cannot really access the success property of the $q promise that you are returning from your function because there is no such property exist, It exists only on the promise directly returned by the http function. So you just need to use the then to chain it through in your controller.
GetPersonData($stateParams.id).then(function(data){ $scope.fullObject = data; });
If you were to return return $http.get('./data/people.json') from your service then you will see the http's custom promise methods success and error.
I want write two services one with a $http.get method and one with $resource
This service should receive a Json Object and looks like this, at the moment this code is direct in my controller and not in a service:
var csvPromise= $http.get(base_url + 'DataSource/1').success(function(data) {
$scope.data4=JSON.stringify(data);
});
The problem is, I want save received data in $scope.data4 and I want use this data after the $http.get call but the value is empty.
Direct after this call there is and Object that needs this value:
new myObject($scope.data4)
so myObject must wait so long until the data has arrived.
or can I make a synchronous call with $http or $resource ?
How can i do this ? I have found so many examples with promise and .then but nothing has worked for me.
EDIT: I have now written a service but it didn`t work:
var test=angular.module('myApp.getCSV', ['ngResource']);
test.factory('getCSV',function($log, $http,$q, $resource){
return {
getData: function (id) {
var csvPromise= $http.get(base_url +'DataSource/'+id)
.success(function(data) {
return data;
});
return csvPromise;
}
}
});
and then in my controller I call this:
getCSV.getData(1).then(function(theData){
$scope.data4=JSON.stringify(theData);
new myObject( $scope.data4); });
but this did not work. I thought if the $http.get receives the data then the then Function is called.
I don't believe you can do synchronous calls. That said, you have at least two options:
1) Pass in the data using the $routeProvider resolve feature. From the documentation:
An optional map of dependencies which should be injected into the controller. If any of these dependencies are promises, the router will wait for them all to be resolved or one to be rejected before the controller is instantiated. If all the promises are resolved successfully, the values of the resolved promises are injected
An example on how to use this:
$routeProvider
.when('/your/path', {
templateUrl: '/app/yourtemplate.html',
controller: 'yourController',
resolve: {
data: ['$route', '$http', function($route, $http) {
return $http.get(base_url +'DataSource/1');
}]
}
})
And then in your controller:
app.controller('yourController', ['$scope', 'data', function($scope, data) {
$scope.data4 = JSON.stringufy(data);
var yourObj = new myObject($scope.data4);
}]);
2) The second option is to use promises and only instantiate your new myObject($scope.data4) once the promise successfully completes.
Your code needs to be changed just a bit:
$scope.data4 = '';
var csvPromise= $http.get(base_url +'DataSource/1');
csvPromise.then(function(data){
$scope.data4 = JSON.stringify(data);
}, function(data){
//error handling should go here
window.alert(data);
});
This should give you what it sounds to me like you need.
As i know, there's no way to sync~ call the http or resource. They're hard coded on AngularJS core file :
xhr.open(method, url, true);
And you don't want to hurt your users too by blocking the browser wait the data arrived. You'll better show how you make the nothing has worked for me so we can start working to fix it.
Have you try call new myObject($scope.data4) inside success method?
$http.get(...).success(function(data){
$scope.data4 = JSON.stringify(data); // I've no idea why do you need this.
var stuff = new myObject($scope.data4); // THis is now your.
});
I need to get some JSON data from the server with Angular. Let's say the user data. I created a service like that:
app.service('User', function($http) {
retrun $http({method: 'GET', url:'/current_user'});
});
And in my controller:
app.controller('SomeCtrl', function($scope, User) {
User.success(function(data) {
$scope.user = data;
});
});
That works just fine but what if I want to add some methods to the user? For instance in the view I would like to do {{user.isAdmin()}}. Is it the correct approach? Where can I add those methods?
If you wanted your service to always return an object with this method, do something like this:
app.service('User', function($http) {
return $http({method: 'GET', url:'/current_user'}).
then(function(response) {
response.data.isAdmin = function() { return true; };
return response.data;
});
});
Now any future code that references this promise and uses .then() will retrieve the new object. Take a look at the promise documentation for more information.
http://docs.angularjs.org/api/ng.$q
Keep in mind by using 'then' on an httpPromise it will be converted to a normal promise. You no longer have the convenience methods 'success' and 'error'.
It may be better practice to create a class for the object you are returning with a constructor function which takes the data object and assigns appropriate properties (or extends the instance). This way you can simply do something like
return new User(val);
And you will get all of the methods you want (with a prototype, etc).
You can do this in a few ways in the service you created:
Start using $resource and use a transform on the response:
http://jsfiddle.net/roadprophet/prtAP/
...
transformResponse: function (data, headers) {
data = {};
data.coolThing = 'BOOM-SHAKA-LAKA';
return data;
}
...
I recommend this method because it scales cleaner due to the use of $resource.
Setup a transformResponse with $http:
http://jsfiddle.net/roadprophet/bPfcz/
Use your own promise that resolves after the get promise resolves but with the mapped data. This is probably the most manual way to handle it since it requires you to manage multiple promises.
Anyone knows what the status of Web Worker support in NodeJS is? I found a two year old implementation, node-webworkers, but it didn't run with the current build of NodeJS.
Now there is https://github.com/audreyt/node-webworker-threads which appears to be actively maintained.
Worker Threads reached stable status in 12 LTS. Usage example
const {
Worker, isMainThread, parentPort, workerData
} = require('worker_threads');
if (isMainThread) {
module.exports = function parseJSAsync(script) {
return new Promise((resolve, reject) => {
const worker = new Worker(__filename, {
workerData: script
});
worker.on('message', resolve);
worker.on('error', reject);
worker.on('exit', (code) => {
if (code !== 0)
reject(new Error(`Worker stopped with exit code ${code}`));
});
});
};
} else {
const { parse } = require('some-js-parsing-library');
const script = workerData;
parentPort.postMessage(parse(script));
}
You can use the child processes, they solve similar problems.
You can look at the specifics of the HTML5 WebWorker source.
With a little care, you can 'redress' the WebWorker to fit as a Node.js worker, by adding a prelude that may look something like this:
const { parentPort } = require('worker_threads')
global.postMessage = function(msg){
parentPort.postMessage(msg)
}
var handler
global.addEventListener = function(kind, callback){
handler = callback
}
parentPort.on('message', msg => {
handler(msg)
})
The specific HTML5 worker added a message event handler using addEventListener, so I registered such a function in global and saved the handler. I also had to supply a postMessage implementation. Finally I registered a Node.js message handler that invokes the HTML5 handler.
Everything works perfectly. No need for any special dependency, just looking at the HTML5 worker code and identify the points where it deals with messages.