I have this code that works:
require! [async]
action = for let m from 1 to 12
(p) ->
p null, m
err, data <- async.series action
console.log data
but I having difficulties to have the code works on a nested loop:
action = for let m from 1 to 12
for let d from 1 to 12
(p) ->
p null, (m + "-" + d)
err, data <- async.series action
console.log data
error message:
fn(function (err) {
^
TypeError: object is not a function
As requested by the comment, the compiled js code, generated by Livescript:
var async, action, res$, i$;
async = require('async');
res$ = [];
for (i$ = 1; i$ <= 12; ++i$) {
res$.push((fn$.call(this, i$)));
}
action = res$;
async.series(action, function(err, data){
return console.log(data);
});
function fn$(m){
var i$, results$ = [];
for (i$ = 1; i$ <= 12; ++i$) {
results$.push((fn$.call(this, i$)));
}
return results$;
function fn$(d){
return function(p){
return p(null, m + "-" + d);
};
}
}
The action you got for the nested loop is probably a nested arrays of closures, like [[fn, fn], [fn, fn]]
so you want to flatten them by concatenating:
err, data <- async.series action.reduce (++)
Related
I am trying to write a function that simply repeats the string 3 times by making a loop inside this function:
repeatString('hey', 3) // returns 'heyheyhey'
so far I have the following code and am trying to make a loop;
const repeatString = function() {
}
module.exports = repeatString
a bit clean way Repeat function
const repeatString = function(str, num) {
return (num < 0) ? new Error("Error") : str.repeat(num);
}
module.exports = repeatString
This is the Code I came up with and worked!
const repeatString = function repeatString( str, num) {
str ='hey';
if (num > 0) {
return str.repeat(num);
} else if (num < 0) {
return 'ERROR';
} else {
return '';
}
}
module.exports = repeatString
Edit:
Here is my full code that throws no errors:
router.get('/:id/all', async (req, res, next) => {
let id = req.params.id;
let t;
let d;
let o;
let p;
let data = [];
let entry = {};
try {
let rowConfig = await methods.runQuery('SELECT SystemID, Begin, End, Power FROM Configuration WHERE ID = ?', id);
p = rowConfig[0].Power;
let begin = rowConfig[0].Begin;
let end = rowConfig[0].End;
let counter = [Var1, Var2, Var3];
let result = await methods.runQuery('SELECT * FROM Table1 WHERE ID = ?', id);
result.forEach(async function(row) {
let resultT;
if (!row.EventStop) {
t = row.EventBegin - begin;
resultT = await methods.runQuery('SELECT EventBegin, EventStop FROM Table1 WHERE ID = ? AND RootID IN (4, 5) AND IsValid = TRUE AND EventBegin < ?', [id, row.EventBegin]);
}
else {
t = row.EventStop - begin;
resultT = await methods.runQuery('SELECT EventBegin, EventStop FROM Table1 WHERE ID = ? AND RootID IN (4, 5) AND IsValid = TRUE AND EventBegin < ?', [id, row.EventStop]);
}
console.log(t);
d = 0;
resultT.forEach(function(row) {
let dt = row.EventStop - row.EventBegin;
d = d + dt;
});
o = t - d;
console.log(o);
entry = {'1': t, '2':o};
data.push({entry});
});
}
catch (error) {
res.status(500).send({ error: true, message: 'Error' });
}
return res.send({ data: data });
});
But the data array that is sent remains emtpy! So i looked in my console and two stand out.
The values of tand o are wrong
They get logged in the console when the get method already has finsihed. So when the data array is sent, obviously there are no entry in there.
The order in which the code should be excuted:
For each row of Table1 i want to have t and o, so it should be:
forEach loop (row1)
-> if/else -> calculate t
-> get resultT
-> forEach loop (row1)
-> calculate d
-> forEach loop (row2)
-> calculate d
-> ...
-> calculate o
-> push entry to data
-> forEach loop (row2)
-> ...
I am working with node and express for creating a Rest API. I am currently struggling because of the asynchronous behaviour of node. This is what I am trying to achieve:
In a get method, I want to collect all the data of table from my database.
router.get('/:id/all', async (req, res, next) => {
...
try {
let result = await methods.runQuery('SELECT SystemID, Begin, End, Power FROM Configuration WHERE ID = ?', id);
The runQuery method looks like this :
module.exports.runQuery = function(sql, parameter){
return new Promise((resolve, reject) => {
dbConn.query(sql, parameter, function (error, result, fields) {
if (error) reject(error);
else {
resolve(result);
}
});
});
}
This works so far. Now my problems start.
For each row of this table I want to do something.
Inside this for loop I need to do calculations that depend on each other.
}
As I have mentioned in the comment, await won't work in forEach loop. Try for...of loop instead.
Example:
for (let row of result) {
// await will work here
}
for/forEach loops in javascript are not promise/async/await aware so you will need to use Promise.all instead of for loop. Basically something like
Promise.all(result.map(result => doSomethingAsync()))
Make sure there are not large data in result as you will be spinning those many promises in parallel. Better will be to use promise batch or streaming.
EDIT: I'm using node v8.0.0
I just started learning how to access SQL databases with node-postgres, and I'm having a little bit of trouble accessing multiple databases to collect the data in a work able format, particularly with executing multiple queries within forEach loops. After a few tries, I'm trying async/await, but I get the following error:
await client.connect()
^^^^^^
SyntaxError: Unexpected identifier
When I tried using a pool or calling .query sequentially, I would get something along the lines of
1
[]
could not connect to postgres Error: Connection terminated
Here is an abbreviated version of my code:
const { Client } = require('pg');
const moment = require('moment');
const _ = require('lodash');
const turf = require('#turf/turf');
const connString = // connection string
var collected = []
const CID = 300
const snaptimes = // array of times
var counter=0;
const client = new Client(connString);
function createArray(i,j) {
// return array of i arrays of length j
}
await client.connect()
snaptimes.forEach(function(snaptime){
var info = {}; // an object of objects
// get information at given snaptime from database 1
const query1 = // parametrized query selecting two columns from database 1
const result1 = await client.query(query1, [CID,snaptime]);
var x = result1.rows;
for (var i = 0; i < x.length; i++) {
// store data from database 1 into info
// each row is an object with two fields
}
// line up subjects on the hole
const query2 = // parametrized query grabbing JSON string from database 2
const result2 = await client.query(query2, [CID,snaptime]);
const raw = result2.rows[0].JSON_col;
const line = createArray(19,0); // an array of 19 empty arrays
for (var i = 0; i < raw.length; i++) {
// parse JSON object and record data into line
}
// begin to collect data
var n = 0;
var g = 0;
// walk down the line
for (var i = 18; i > 0; i--) {
// if no subjects are found at spot i, do nothing, except maybe update g
if ((line[i] === undefined || line[i].length == 0) && g == 0){
g = i;
} else if (line[i] !== undefined && line[i].length != 0) {
// collect data for each subject if subjects are found
line[i].forEach(function(subject){
const query 3 = // parametrized query grabbing data for each subject
const result3 = await client.query(query3,[CID,subject,snaptime]);
x = result3.rows;
const y = moment(x[0].end_time).diff(moment(snaptime),'minutes');
var yhat = 0;
// the summation over info depends on g
if (g===0){
for (var j = i; j <= 18; j++){
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
} else {
for (var j = i; j <= 18; j++){
if (i<j && j<g+1) {
yhat = moment.duration(info[j].field2).add(yhat,'m').asMinutes();
} else {
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
}
}
collected.push([y,yhat,n,i]);
});
}
n+=line[i].length;
g=0;
}
// really rough work-around I once used for printing results after a forEach of queries
counter++;
if (counter===snaptimes.length){
console.log(counter);
console.log(collected);
client.end();
}
});
The problem is caused by your forEach callback not being async:
snaptimes.forEach(function(snaptime){
should be:
snaptimes.forEach(async function (snaptime) {
for the await to be recognizable at all.
Keep in mind that an async function returns immediately and it returns a promise that gets eventually resolved by return statements of the async function (or rejected with uncaught exceptions raised inside the async function).
But also make sure your Node version supports async/await:
Since Node 7.6 it can be used with no --harmony flag.
In Node 7.x before 7.6 you have to use the --harmony flag.
It was not available in Node before 7.0.
See: http://node.green/#ES2017-features-async-functions
Also note that you can use await only inside of functions declared with the async keyword. If you want to use it in the top level of your script or module then you need to wrap it in an immediately invoked function expression:
// cannot use await here
(async () => {
// can use await here
})();
// cannot use await here
Example:
const f = () => new Promise(r => setTimeout(() => r('x'), 500));
let x = await f();
console.log(x);
prints:
$ node t1.js
/home/rsp/node/test/prom-async/t1.js:3
let x = await f();
^
SyntaxError: Unexpected identifier
but this:
const f = () => new Promise(r => setTimeout(() => r('x'), 500));
(async () => {
let x = await f();
console.log(x);
})();
prints:
$ node t2.js
x
after 0.5s delay, as expected.
On versions of Node that don't support async/await the first (incorrect) example will print:
$ ~/opt/node-v6.7.0/bin/node t1.js
/home/rsp/node/test/prom-async/t1.js:3
let x = await f();
^
SyntaxError: Unexpected identifier
and the second (correct) example will print a different error:
$ ~/opt/node-v6.7.0/bin/node t2.js
/home/rsp/node/test/prom-async/t2.js:3
(async () => {
^
SyntaxError: Unexpected token (
It's useful to know because Node versions that don't support async/await will not give you a meaningful error like "async/await not supported" or something like that, unfortunately.
Make sure that you should use async block outside like:
async function() {
return await Promise.resolve('')
}
And it is default supported after node 7.6.0. Before 7.6.0, you should use --harmony option to work for it.
node -v first to check your version.
First of all, you don't know enough about async-await just yet. don't worry, it's actually quite easy; but you need to read the documentation to be able to use that stuff.
More to the point, the problem with your code is that you can only await inside async functions; you're doing that outside of any function.
First of all, here's the solution that is closest to the code you wrote:
const { Client } = require('pg');
const moment = require('moment');
const _ = require('lodash');
const turf = require('#turf/turf');
const connString = // connection string
var collected = []
const CID = 300
const snaptimes = // array of times
var counter=0;
const client = new Client(connString);
function createArray(i,j) {
// return array of i arrays of length j
}
async function processSnaptime (snaptime) {
var info = {}; // an object of objects
// get information at given snaptime from database 1
const query1 = // parametrized query selecting two columns from database 1
const result1 = await client.query(query1, [CID,snaptime]);
var x = result1.rows;
for (var i = 0; i < x.length; i++) {
// store data from database 1 into info
// each row is an object with two fields
}
// line up subjects on the hole
const query2 = // parametrized query grabbing JSON string from database 2
const result2 = await client.query(query2, [CID,snaptime]);
const raw = result2.rows[0].JSON_col;
const line = createArray(19,0); // an array of 19 empty arrays
for (var i = 0; i < raw.length; i++) {
// parse JSON object and record data into line
}
// begin to collect data
var n = 0;
var g = 0;
// walk down the line
for (var i = 18; i > 0; i--) {
// if no subjects are found at spot i, do nothing, except maybe update g
if ((line[i] === undefined || line[i].length == 0) && g == 0){
g = i;
} else if (line[i] !== undefined && line[i].length != 0) {
// collect data for each subject if subjects are found
line[i].forEach(function(subject){
const query 3 = // parametrized query grabbing data for each subject
const result3 = await client.query(query3,[CID,subject,snaptime]);
x = result3.rows;
const y = moment(x[0].end_time).diff(moment(snaptime),'minutes');
var yhat = 0;
// the summation over info depends on g
if (g===0){
for (var j = i; j <= 18; j++){
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
} else {
for (var j = i; j <= 18; j++){
if (i<j && j<g+1) {
yhat = moment.duration(info[j].field2).add(yhat,'m').asMinutes();
} else {
yhat = moment.duration(info[j].field1).add(yhat,'m').asMinutes();
}
}
}
collected.push([y,yhat,n,i]);
});
}
n+=line[i].length;
g=0;
}
// really rough work-around I once used for printing results after a forEach of queries
counter++;
if (counter===snaptimes.length){
console.log(counter);
console.log(collected);
}
}
async function run () {
for (let snaptime of snaptimes) {
await processSnaptime(snaptime);
}
}
/* to run all of them concurrently:
function run () {
let procs = [];
for (let snaptime of snaptimes) {
procs.push(processSnaptime(snaptime));
}
return Promise.all(procs);
}
*/
client.connect().then(run).then(() => client.end());
client.connect returns a promise and I use then to call run once it's resolved. When that part is over, client.end() can be called safely.
run is an async function, therefore it can use await to make the code more readable. The same goes for processSnaptime.
Of course I can't actually run your code, so I can only hope I didn't make any mistakes.
I have created a generator function that recursively checks a string and returns a parsed output. I am trying to make a request within the generator using koa-request however, it is returning undefined.
var parseUserExpression = function *() {
var body = yield bodyParser.json(this);
var fnString = body.ts;
var res = yield parseRulesAndFunctions(fnString, null);
this.body = res;
};
// Recursive function
var parseRulesAndFunctions = function *(aStr, start) {
var res;
start = start || 0;
var fnDetails = getFnDetails(aStr, start);
if (fnDetails.fnType === 'run') {
var url = yield request(fnDetails.url);
res = aStr.slice(0, fnDetails.startIndex) + 'yield request(' + fnDetails.fnName + ',' + fnDetails.fnParams + aStr.slice(fnDetails.endIndex);
}
// Recurse
if (res.indexOf('call') === -1 && res.indexOf('run') === -1) {
return res;
}
return parseRulesAndFunctions(res, fnDetails.paramEnd).next();
}
Returns the Promise instead of a string when yielding the request(fnDetails.url).
If you are recursively calling a generator function, you must yield all results from the generator. You can do that using yield*. Only returning a single .next() result won't do it.
You're looking for
return yield* parseRulesAndFunctions(res, fnDetails.paramEnd);
Of course, you could easily convert your tail-recursive function into a loop.
I have this collection in MongoDB (I'm omitting _ids for brevity):
test> db.entries.find();
{
"val": 1
}
{
"val": 2
}
{
"val": 3
}
{
"val": 4
}
{
"val": 5
}
I need to perform some processing on each document which I cannot do with db.update(). So, in a nutshell, what I need to do is retrieving one document at a time, process it in Node and save it back to Mongo.
I'm using the Monk library, and Q for promises. Here's what I've done — I didn't include the processing/save bit for brevity:
var q = require('q');
var db = require('monk')('localhost/test');
var entries = db.get('entries');
var i = 1;
var total;
var f = function (entry) {
console.log('i = ' + i);
console.log(entry.val);
i++;
if (i <= total) {
var promise = entries.findOne({ val: i });
loop.then(function (p) {
return f(p);
});
return promise;
}
};
var loop = q.fcall(function () {
return entries.count({});
}).then(function (r) {
total = r;
return entries.findOne({ val: i });
}).then(f);
I would expect this code to print out:
i = 1
1
i = 2
2
i = 3
3
i = 4
4
i = 5
5
but it actually prints out:
i = 1
1
i = 2
2
i = 3
2
i = 4
2
i = 5
2
What am I doing wrong?
In your code, loop is one and only one promise. It is executed only once. It is not a function.
Inside f, loop.then(f) just trigger f with the result of the promise (it has already been executed so it is not executed again).
You actually want to create several promises.
What you are looking for is something that should looks like:
var q = require('q');
var db = require('monk')('localhost/test');
var entries = db.get('entries');
var i = 1;
var total;
var f = function (entry) {
console.log('i = ' + i);
console.log(entry.val);
i++;
if (i <= total) {
// I am not sure why you put entries.findOne here (looks like a mistake,
// its returned value isn't used) but if you really need it to be done
// before loop, then you must pipe it before loop
return entries.findOne({ val: i }).then(loop);
// do not pipe f again here, it is already appended at the end of loop
}
};
function loop(){
return q.fcall(function () {
return entries.count({});
}).then(function (r) {
total = r;
return entries.findOne({ val: i });
}).then(f);
}
loop();
If you are interested, here is a very nice article about promises.