I'm struggling to retrieve data from firebase. basically im creating a dating app and when a user "likes" someone, it should check the displayed users liked people array to see if the current user is in there and then "match" them if they are
I have this function:
pullFromFirebase = (displayedUser) => {
return new Promise((resolve, reject) => {
firebase.database().ref('users/' + displayedUser.id + '/usersLiked/').once('value').then(function(snapshot) {
const users = Object.keys(snapshot.val()).map(function(key) {
return snapshot.val()[key];
})
});
})
}
This function is working, coz when I console.log(users), I get the array of the people who are liked. however, when I call this function like so
async checkForMatch (currentUser, displayedUser) {
const likedUsers = await this.pullFromFirebase(displayedUser);
console.log(likedUsers, 'likedUsers');
}
nothing is being logged in the console? and when I take away the async stuff, the console.log just says it's pending. what have i done wrong or why cant i get the users displayed in my checkformatch function?
you never resolved your promise in pullFromFirebase method
checkout the code
pullFromFirebase = (displayedUser) =>
{
return new Promise((resolve, reject) =>
{
firebase.database().ref('users/' + displayedUser.id + '/usersLiked/').once('value').then(function (snapshot)
{
const users = Object.keys(snapshot.val()).map(function (key) {
return snapshot.val()[key];
})
resolve(users); // <--- here is the fix
});
})
}
You may have added a Promise there unnecessairily and your function returns a Promise which never resolves. firebase.database returns a Promise already but you also need to return the users you get within .then():
pullFromFirebase = (displayedUser) => {
return firebase.database().ref('users/' + displayedUser.id + '/usersLiked/').once('value').then(function(snapshot) {
const users = Object.keys(snapshot.val()).map(function(key) {
return snapshot.val()[key];
});
return users;
});
}
Or alternately, if you need that wrapping Promise you need to resolve it with the return value:
pullFromFirebase = (displayedUser) => {
return new Promise((resolve, reject) => {
firebase.database().ref('users/' + displayedUser.id + '/usersLiked/').once('value').then(function(snapshot) {
const users = Object.keys(snapshot.val()).map(function(key) {
return snapshot.val()[key];
})
resolve(users);
});
})
}
Related
I have few api call requests which i am trying to create promises and then execute all using Promise.all but, its giving empty value instead of array. Below is my code.
function getUser(arrUser) {
var student = [];
return new Promise((resolve, reject) => {
if (arrUser.length > 0) {
var promises = arrUseridRequest.map(userRequeset => {
return getRequest(userRequeset).then(result => {
student.push(JSON.parse(result.body).result[0].Name);
console.log(student); //This is giving right details.
}).catch(error => {
reject(error);
});
});
Promise.all(promises).then(StuName => {
resolve(StuName.join());
})
}
});
}
and this is how i am trying to get the values at once:
getUser('123').then(student => {
console.log(Student) //Coming as empty
});
getRequest is my api call nodeJs request module. What's wrong in my code?
All your promises fulfill with the value undefined since you're just logging the student names, but not returning them from the then callback. As you seem to be doing only a single request, the array will be [undefined], which is joined into the empty string.
Also avoid the Promise constructor antipattern:
function getUsers(arrUser) {
const promises = arrUser.map(userId => {
return getRequest(userId).then(result => {
const students = JSON.parse(result.body).result;
return students[0].Name;
});
});
return Promise.all(promises);
}
getUsers(['123']).then(studentNames => {
console.log(studentNames);
console.log(studentNames.join());
}).catch(console.error);
In node.js i have a databaseMapper.js file, that uses the Ojai node MapR api. to extract data. So far i have it working with single documents, but since this is an async api, i have a bit of issues with querying multiple documents.
This is what i have so far:
function queryResultPromise(queryResult) {
//this should handle multiple promises
return new Promise((resolve, reject) => {
queryResult.on("data", resolve);
// ...presumably something here to hook an error event and call `reject`...
});
}
const getAllWithCondition = async (connectionString, tablename, condition) =>{
const connection = await ConnectionManager.getConnection(connectionString);
try {
const newStore = await connection.getStore(tablename);
const queryResult = await newStore.find(condition);
return await queryResultPromise(queryResult);
} finally {
connection.close();
}
}
here it will only return the first because queryResultPromise will resolve on the first document.. however the callback with "data" may occur multiple times, before the queryResult will end like this queryResult.on('end', () => connection.close())
i tried using something like Promise.all() to resolve all of them, but I'm not sure how i include the queryResult.on callback into this logic
This will work
const queryResultPromise = (queryResult) => {
return new Promise((resolve, reject) => {
let result = [];
queryResult.on('data', (data) => {
result.push(data)
});
queryResult.on('end', (data) => {
resolve(result);
});
queryResult.on('error', (err) => {
reject(err);
})
});
};
Previously I was using like this:
Opening Maxmind db in Nodejs
Now, updated the modules as per node 10.
So, need help to integrate it.
reference
const maxmind = require('maxmind');
exports.getIsoCountry = function(pIpAddress) {
modules.debugLog('inside getIsoCountry : ',pIpAddress);
maxmind.open(sGlAppVariable.maxmindDbPath)
.then(function(lookup) {
var ipData = lookup.get(pIpAddress);
//console.log(ipData);
console.log('iso_code',ipData.country.iso_code);
return ipData.country.iso_code;
});
}
console.log(getIsoCountry('66.6.44.4')); it should print country code. but it is undefined always. because this is a promise.
How to call this getIsoCountry function?
Any help will be appreciated.
You need to wait for execution to complete, for that, you should use Promise.
Modify your code as below, then it should work:
const maxmind = require('maxmind');
exports.getIsoCountry = function(pIpAddress) {
return new Promise((resolve, reject) => {
modules.debugLog('inside getIsoCountry : ',pIpAddress);
maxmind.open(sGlAppVariable.maxmindDbPath)
.then(function(lookup) {
var ipData = lookup.get(pIpAddress);
console.log('iso_code',ipData.country.iso_code);
resolve(ipData.country.iso_code);
});
});
}
getIsoCountry("66.6.44.4").then((rData) => {
console.log(rData)
});
Below is sample code:
var getIsoCountry = function(pIpAddress) {
return maxmind().then(function() {
return "Code for IP: " + pIpAddress;
});
function maxmind() {
return new Promise((resolve, reject) => {
resolve("done")
});
}
}
getIsoCountry("1.1.1.1").then((data) => {
console.log(data)
});
In my AngularJS Application, I want to access the return value of a Promise, which I access from a service outside of my controller and import it there. This Promise, return an object. I want to access that objects and properties inside it.
I created the service to get that endpoint. Look below:
export const getEndpoints = () => {
const options = {
method: httpMethod.GET,
url: endpoint.ENVIRONMENT,
};
return Instance(options);
};
The above service in return reads an endpoint which I provide and uses axios on the background. This part is working just fine.
Then imported it, on my angular Controller:
import { getEndpoints } from './config/service';
Finally I created this function:
$scope.isItAvailable = false; // I will use this later to check the actual value. It is not important in the scope of the question..
const checkIfItIsAvailable = () => {
return new Promise((resolve, reject) => {
resolve(getEndpoints)
console.log(getEndpoints)
})
}
// And in my main function I am just calling the above
const mainFn = () => {
checkIfItIsAvailable()
// Along with a few others..
}
Actual Results
Now, in my console, I get the functioncheckIfItAvailable printed out.
Expected Results
I instead want to print to the console, the actual value that is being returned by the original promise, the object, and its properties.
Probably You need to call that function instead of just passing it as a parameter.
const checkIfItIsAvailable = () => {
return new Promise((resolve, reject) => {
resolve(getEndpoints()) // here
console.log(getEndpoints())
})
}
Then to get that resolved later in your main function, or wherever - just use then:
const mainFn = () => {
checkIfItIsAvailable().then((result) => {
// do what you need with result here
// $scope.isItAvailable = result probably like this
});
}
Please comment if you need another result. I see at least this issue at the moment.
Also, here is a snipper, illustrating that you need to call it instead of just passing.
// here is an example function which just return some string
function getSomething() {
return 'something'; // it could be a promise also
}
// here is example without calling functions, but just passing:
const promise = new Promise((resolve, reject) => {
console.log('NO CALL: ', getSomething);
});
// here is example with calling, so value is resolved
const promise2 = new Promise((resolve, reject) => {
console.log('CALLED: ', getSomething());
});
Here, getEndpoints is an asynchronous function which returns a Promise, and the way to get a return value from promise is to use then callback. You can do it like this:
const checkIfItIsAvailable = () => {
return new Promise((resolve, reject) => {
getEndpoints().then(resultOfEndPoint => {
console.log(resultOfEndPoint);
resolve(resultOfEndPoint);
});
})
}
It's possible to access the resolved result of getEndpoints in checkIfItIsAvailable calling getEndpoints() and using then() function:
const checkIfItIsAvailable = () => {
return new Promise((resolve, reject) => {
// call getEndpoints
getEndpoints()
// call then to get a result from getEndpoints
.then(res => {
console.log(res);
// checkIfItIsAvailable will be resolved with
// the result of getEndpoints
resolve(res);
});
});
}
I'm struggling to wrap my head around a nested promise layout where one one object is returned at the end of it. My current code is as follows:
router
router.get(`/${config.version}/event/:id?`, function (req, res, next) {
var event = new Event(req, res, next);
event.getInfo(req.params.id).then((info) => {
res.send(info);
});
});
function
getInfo(id) {
db.main('events').where('id', id).select()
.then((result) => {
if(result.length > 0) {
var event = result[0];
//regular functions
event.status = this.getStatus(id);
event.content = this.getContent(id);
event.price = this.getPrice(id);
//promise functions
var users = this.getUsers(id);
var hosts = this.getHosts(id);
Promise.all([users, hosts]).then(values => {
event.users = values[0];
event.hosts = values[1];
//return whole event object to router
return event;
})
.catch((err) => {
return {
result: 'error',
error: err
};
});
} else {
return {
result: 'error',
error: "Event does not exist"
};
}
}).catch((e) => {
return {
result: 'error',
error: "Could not retrieve event info"
};
});
}
As you can see, the router initiates a call to get info about an event. The function then does a database call and gets some event data. Thereafter I need to get the users and hosts of the event from a different table, append that info to the event object as well and then return the whole object to the router to be sent to the client.
When I do this I get an error because I'm not returning a promise from the getInfo function, but I'm not sure how or which promise I'm supposed to return.
I'd appreciate some help with this. Thanks
using .then means that you are returning a promise.
function getInfo(id) {
return new Promise(function(resolve, reject) {
resolve('yay!');
})
}
getInfo().then(function(result) { //result = yay! });
to make your code work, simply replace all the returns with resolves, the errors with rejects, and wrap the whole thing with a return new Promise as i did.
getInfo(id) {
return new Promise(function(resolve, reject) {
db.main('events').where('id', id).select()
.then((result) => {
if (result.length > 0) {
var event = result[0];
//regular functions
event.status = this.getStatus(id);
event.content = this.getContent(id);
event.price = this.getPrice(id);
//promise functions
var users = this.getUsers(id);
var hosts = this.getHosts(id);
Promise.all([users, hosts]).then(values => {
event.users = values[0];
event.hosts = values[1];
//return whole event object to router
resolve(event);
})
.catch((err) => {
reject({
result: 'error',
error: err
});
});
} else {
reject({
result: 'error',
error: "Event does not exist"
});
}
}).catch((e) => {
reject({
result: 'error',
error: "Could not retrieve event info"
});
});
});
}
Just wrap your async code in Promise like this:
getInfo(id) {
return new Promise(function(resolve, reject) {
db.main('events').where('id', id).select()
.then((result) => {
//...
resolve(/* result */)
// OR
reject(/* Error */)
})
}
Note: Use resolve and reject instead return
It's a combination of several things, but the main one is that you are never returning anything from getInfo, so your router handler is calling .then on undefined.
Do not call .catch (without throwing inside it) on Promises you intend to return for a caller to consume. This makes it not possible to use .catch, because you recovered the Promise chain into a resolved one.
Whatever you return inside a .then will be merged into the promise chain, so it's not actually a "Promise that resolves with a Promise". Your whole code could be replaced with:
getInfo (id) {
return db.main('events').where('id', id).select()
.then(result => {
if (result.length == 0) {
// you can also just throw your error object thing,
// but standard Error are generally the convention
throw new Error('Event does not exist')
}
const [event] = result
event.status = this.getStatus(id)
event.content = this.getContent(id)
event.price = this.getPrice(id)
return Promise.all([this.getUsers(id), this.getHosts(id)])
.then(([users, hosts]) => {
event.users = users
event.hosts = hosts
// this is the only value that
// this.getInfo(id).then(value => {/* ... */}) will see
return event
}
})
}