I am new to the Promise method used to retrieve multiple database records at the same time and I want to rewrite my existing code to use promises
I have this piece of code in Express:
getController.getData = function(req,res, collection, pagerender) {
var id = req.params.id;
collection.find({}, function(err, docs){
if(err) res.json(err);
else res.render(pagerender, {data:docs, ADusername: req.session.user_id, id: req.params.id});
console.log(docs);
});
};
Now I want to use promises here, so I can do more queries to the database. Anyone know how I can get this done?
First, check if collection.find({}) returns a promise. If it does, then you can call your code like:
collection.find({}).
then(function(docs){
res.render(pagerender, {data:docs, ADusername: req.session.user_id, id: req.params.id});
})
.catch( function(err) {
res.json(err);
})
If you want more calls here, just create new DB call and add another .then block.
I suggest you read the documentation on promises, just to get a general feeling about them (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then). You will also see how you can handle both success and rejection in the same function if you want.
Related
I have been trying to use the value from the JSON that I have got added successfully using fs.write() function,
There are two test cases in the same fixture, one to create an ID and 2nd to use that id. I can wrote the id successfully in the json file using fs.write() function and trying to use that id using importing json file like var myid=require('../../resources/id.json')
The json file storing correct id of the current execution but I get the id of first test execution in 2nd execution.
For example, id:1234 is stored during first test execution and id:4567 is stored in 2nd test execution. During 2nd test execution I need the id:4567 but I get 1234 this is weird, isn't it?
I use it like
t.typeText(ele, myid.orid)
my json file contains only id like {"orid":"4567"}
I am new to Javascript and Testcafe any help would really be appreciated
Write File class
const fs = require('fs')
const baseClass =require('../component/base')
class WriteIntoFile{
constructor(orderID){
const OID = {
orderid: orderID
}
const jsonString = JSON.stringify(OID)
fs.writeFile(`resources\id.json`, jsonString, err => {
if (err) {
console.log('Error writing file', err)
} else {
console.log('Successfully wrote file')
}
})
}
}
export default WriteIntoFile
I created 2 different classes in order to separate create & update operations and call the functions of create & update order in single fixture in test file
Create Order class
class CreateOrder{
----
----
----
async createNewOrder(){
//get text of created ordder and saved order id in to the json file
-----
-----
-----
const orId= await baseclass.getOrderId();
new WriteIntoFile(orId)
console.log(orId)
-----
-----
-----
}
}export default CreateOrder
Update Order class
var id=require('../../resources/id.json')
class UpdateOrder{
async searchOrderToUpdate(){
await t
***//Here, I get old order id that was saved during previous execution***
.typeText(baseClass.searchBox, id.orderid)
.wait(2500)
.click(baseClass.searchIcon)
.doubleClick(baseClass.orderAGgrid)
console.log(id.ordderid)
----
----
async updateOrder(){
this.searchOrderToUpdate()
.typeText(baseClass.phNo, '1234567890')
.click(baseClass.saveBtn)
}
}export default UpdateOrder
Test file
const newOrder = new CreateOrder();
const update = new UpdateOrder();
const role = Role(`siteurl`, async t => {
await t
login('id')
await t
.wait(1500)
},{preserveUrl:true})
test('Should be able to create an Order', async t=>{
await newOrder.createNewOrder();
});
test('Should be able to update an order', async t=>{
await update.updateOrder();
});
I'll reply to this, but you probably won't be happy with my answer, because I wouldn't go down this same path as you proposed in your code.
I can see a couple of problems. Some of them might not be problems right now, but in a month, you could struggle with this.
1/ You are creating separate test cases that are dependent on each other.
This is a problem because of these reasons:
what if Should be able to create an Order doesn't run? or what if it fails? then Should be able to update an order fails as well, and this information is useless, because it wasn't the update operation that failed, but the fact that you didn't meet all preconditions for the test case
how do you make sure Should be able to create an Order always runs before hould be able to update an order? There's no way! You can do it like this when one comes before the other and I think it will work, but in some time you decide to move one test somewhere else and you are in trouble and you'll spend hours debugging it. You have prepared a trap for yourself. I wrote this answer on this very topic, you can read it.
you can't run the tests in parallel
when I read your test file, there's no visible hint that the tests are dependent on each other. Therefore as a stranger to your code, I could easily mess things up because I have no way of knowing about it without going deeper in the code. This is a big trap for anyone who might come to your code after you. Don't do this to your colleagues.
2/ Working with files when all you need to do is pass a value around is too cumbersome.
I really don't see a reason why you need to same the id into a file. A slightly better approach (still violating 1/) could be:
const newOrder = new CreateOrder();
const update = new UpdateOrder();
// use a variable to pass the orderId around
// it's also visible that the tests are dependent on each other
let orderId = undefined;
const role = Role(`siteurl`, async t => {
// some steps, I omit this for better readability
}, {preserveUrl: true})
test('Should be able to create an Order', async t=>{
orderId = await newOrder.createNewOrder();
});
test('Should be able to update an order', async t=>{
await update.updateOrder(orderId);
});
Doing it like this also slightly remedies what I wrote in 1/, that is that it's not visible at first sight that the tests are dependent on each other. Now, this is a bit improved.
Some other approaches how you can pass data around are mentioned here and here.
Perhaps even a better approach is to use t.fixtureCtx object:
const newOrder = new CreateOrder();
const update = new UpdateOrder();
const role = Role(`siteurl`, async t => {
// some steps, I omit this for better readability
}, {preserveUrl:true})
test('Should be able to create an Order', async t=>{
t.fixtureCtx.orderId = await newOrder.createNewOrder();
});
test('Should be able to update an order', async t=>{
await update.updateOrder(t.fixtureCtx.orderId);
});
Again, I can at least see the tests are dependent on each other. That's already a big victory.
Now back to your question:
During 2nd test execution I need the id:4567 but I get 1234 this is weird, isn't it?
No, it's not weird. You required the file:
var id = require('../../resources/id.json')
and so it's loaded once and if you write into the file later, you won't read the new content unless you read the file again. require() is a function in Node to load modules, and it makes sense to load them once.
This demonstrates the problem:
const idFile = require('./id.json');
const fs = require('fs');
console.log(idFile); // { id: 5 }
const newId = {
'id': 7
};
fs.writeFileSync('id.json', JSON.stringify(newId));
// it's been loaded once, you won't get any other value here
console.log(idFile); // { id: 5 }
What you can do to solve the problem?
You can use fs.readFileSync():
const idFile = require('./id.json');
const fs = require('fs');
console.log(idFile); // { id: 5 }
const newId = {
'id': 7
};
fs.writeFileSync('id.json', JSON.stringify(newId));
// you need to read the file again and parse its content
const newContent = JSON.parse(fs.readFileSync('id.json'));
console.log(newContent); // { id: 7 }
And this is what I warned you against in the comment section. That this is too cumbersome, inefficient, because you write to a file and then read from the file just to get one value.
What you created is not very readable either:
const fs = require('fs')
const baseClass =require('../component/base')
class WriteIntoFile{
constructor(orderID){
const OID = {
orderid: orderID
}
const jsonString = JSON.stringify(OID)
fs.writeFile(`resources\id.json`, jsonString, err => {
if (err) {
console.log('Error writing file', err)
} else {
console.log('Successfully wrote file')
}
})
}
}
export default WriteIntoFile
All these operations for writing into a file are in a constructor, but a constructor is not the best place for all this. Ideally you have only variable assignments in it. I also don't see much reason for why you need to create a new class when you are doing only two operations that can easily fit on one line of code:
fs.writeFileSync('orderId.json', JSON.stringify({ orderid: orderId }));
Keep it as simple as possible. it's more readable like so than having to go to a separate file with the class and decypher what it does there.
I'm looking for a way to store the results of this select query like a "rank" chart for a game but I'm not sure if what I'm encountering is an async issue or a data-type issue or something else entirely. Any thoughts?
var ranksVar = [];
db.all("select * from user", function(err, rows){
if(err) {
throw err;
} else {
setValue(rows);
}
});
function setValue(value) {
ranksVar = value;
console.log(ranksVar);
}
I've found out a useful post about using SQLite with NodeJS and it gives you the basic examples needed to understand how to use it. Here it is: SQLite NodeJS
In your case, look under the section data query.
Here the example code:
const sqlite3 = require('sqlite3').verbose();
// open the database
let db = new sqlite3.Database('./db/chinook.db');
let sql = `SELECT DISTINCT Name name FROM playlists
ORDER BY name`;
db.all(sql, [], (err, rows) => {
if (err) {
throw err;
}
rows.forEach((row) => {
console.log(row.name);
});
});
// close the database connection
db.close();
As you can see, the rows variable is (I guess) a special type created by the module. To get all data from it, you might want to iterate over it and push it into your array variable.
Cheers 😁 !
I figured out the issue. It was a data type/async issue, I was trying to print a string for an undefined array.
Went back a loop and used the JSON.stringify method to display the array objects correctly.
I'm trying to get different chunks of data from a trello API using bluebird promises library. In my express router I'm using middleware isLoggedIn, and getBoards, which body looks something like:
trello.get("/1/members/me/boards") // resolves with array of board objects
.each((board) => {
// do some async stuff like saving board to db or other api calls, based on retrieved board
.catch(err => console.error('ERR: fetching boards error - ${err.message}'))
})
The question is: I want to redirect (res.redirect('/')) only when all boards were retrieved and saved. How can I do that? Where should I place xres.redirect('/') expression?
I think you need something like:
var Promise = require('bluebird');
var promises = [];
trello.get("/1/members/me/boards") // resolves with array of board objects
.each((board) => {
//
promises.push( /*some promisified async call that return a promise, saving data in db or whatever asynchronous action. The important bit is that this operation must return a Promise. */ );
});
//So now we have an array of promises. The async calls are getting done, but it will take time, so we work with the promises:
Promise.all(promises).catch(console.log).then( function(results){
/*This will fire only when all the promises are fullfiled. results is an array with the result of every async call to trello. */
res.redirect('/'); //now we are safe to redirect, all data is saved
} );
EDIT:
Actually, you can avoid some boilerplate code using map instead of each:
trello.get("/1/members/me/boards") // resolves with array of board objects
.map((board) => {
return somePromisifiedSaveToDbFunction(board);
}).all(promises).catch(console.log).then( function(results){
res.redirect('/');
} );
I'm new to using mongoose middleware and don't know if I'm following it well. Here is the purpose. After saving department, I want to populate university and save departmentId inside university object.
DepartmentSchema.post('save', function(next) {
var departmentId = this._id;
University.findOne({
_id: this.university
}, function(err, university) {
if (!university.departments) {
university.departments = [];
}
university.departments.push(new ObjectId(departmentId));
university.save(function(err) {
if (err) return console.log('err-->' + err);
// saved!
});
});
});
This is working fine but I'm not sure why in Cascade style delete in Mongoose they have used exec() and next() calls. Could you please tell me the purpose of these calls? I don't know what they do and not able to find relevant documentation. I just want to make sure I'm not missing anything.
clientSchema.pre('remove', function(next) {
// 'this' is the client being removed. Provide callbacks here if you want
// to be notified of the calls' result.
Sweepstakes.remove({
client_id: this._id
}).exec();
Submission.remove({
client_id: this._id
}).exec();
next();
});
Post middleware doesn't have reference to the next function and you cant do any flow control. Its actually passing the department that just got saved, so your code can be something like this:
DepartmentSchema.post('save', function(department) {
var departmentId = department._id;
In pre middleware you have access to the next middleware in the order of execution. Which is the order of definition on a particular hook.
// hook two middlewares before the execution of the save method
schema.pre('save', pre1);
schema.pre('save', pre2);
function pre1(next) {
// next is a reference to pre2 here
next()
}
function pre2(next) {
// next will reference the hooked method, in this case its 'save'
next(new Error('something went wrong');
}
// somewhere else in the code
MyModel.save(function(err, doc) {
//It'll get an error passed from pre2
});
Mongoose also gives you the ability to execute pre middlewares in parallel, in this case all middlewares will be executed in parallel but hooked method will not execute till the done is called from each middleware.
As for the exec() function, there are two ways of executing a query in Mongoose, either pass a callback to the query or chain it with an exec(): User.remove(criteria, callback) or User.remove(criteria).exec(callback), if you don't pass a callback to the query, it'll return a query object and it won't execute unless you chain it with exec()
I'd like to use custom headers to provide some more information about the response data. Is it possible to get the headers in a response from a dojo datagrid hooked up to a jsonRest object via an object store (dojo 1.7)? I see this is possible when you are making the XHR request, but in this case it is being made by the grid.
The API provides an event for a response error which returns the response object:
on(this.grid, 'FetchError', function (response, req) {
var header = response.xhr.getAllResponseHeaders();
});
using this I am successfully able to access my custom response headers. However, there doesn't appear to be a way to get the response object when the request is successful. I have been using the undocumented private event _onFetchComplete with aspect after, however, this does not allow access to the response object, just the response values
aspect.after(this.grid, '_onFetchComplete', function (response, request)
{
///unable to get headers, response is the returned values
}, true);
Edit:
I managed to get something working, but I suspect it is very over engineered and someone with a better understanding could come up with a simpler solution. I ended up adding aspect around to allow me to get hold of the deferred object in the rest store which is returned to the object store. Here I added a new function to the deffered to return the headers. I then hooked in to the onFetch of the object store using dojo hitch (because I needed the results in the current scope). It seems messy to me
aspect.around(restStore, "query", function (original) {
return function (method, args) {
var def = original.call(this, method, args);
def.headers = deferred1.then(function () {
var hd = def.ioArgs.xhr.getResponseHeader("myHeader");
return hd;
});
return def;
};
});
aspect.after(objectStore, 'onFetch', lang.hitch(this, function (response) {
response.headers.then(lang.hitch(this, function (evt) {
var headerResult = evt;
}));
}), true);
Is there a better way?
I solved this today after reading this post, thought I'd feed back.
dojo/store/JsonRest solves it also but my code ended up slightly different.
var MyStore = declare(JsonRest, {
query: function () {
var results = this.inherited(arguments);
console.log('Results: ', results);
results.response.then(function (res) {
var myheader = res.xhr.getResponseHeader('My-Header');
doSomethingWith(myheader);
});
return results;
}
});
So you override the normal query() function, let it execute and return its promise, and attach your own listener to its 'response' member resolving, in which you can access the xhr object that has the headers. This ought to let you interpret the JsonRest result while fitting nicely into the chain of the query() all invokers.
One word of warning, this code is modified for posting here, and actually inherited from another intermediary class that also overrode query(), but the basics here are pretty sound.
If what you want is to get info from the server, also a custom key-value in the cookie can be a solution, that was my case, first I was looking for a custom response header but I couldn't make it work so I did the cookie way getting the info after the grid data is fetched:
dojo.connect(grid, "_onFetchComplete", function (){
doSomethingWith(dojo.cookie("My-Key"));
});
This is useful for example to present a SUM(field) for all rows in a paginated datagrid, and not only those included in the current page. In the server you can fetch the COUNT and the SUM, the COUNT will be sent in the Content-Range header and the SUM can be sent in the cookie.