nodejs pg transactions without nesting - node.js

I would like to know if it's possible to run a series of SQL statements and have them all committed in a single transaction.
The scenario I am looking at is where an array has a series of values that I wish to insert into a table, not individually but as a unit.
I was looking at the following item which provides a framework for transactions in node using pg. The individual transactions appear to be nested within one another so I am unsure of how this would work with an array containing a variable number of elements.
https://github.com/brianc/node-postgres/wiki/Transactions
var pg = require('pg');
var rollback = function(client, done) {
client.query('ROLLBACK', function(err) {
//if there was a problem rolling back the query
//something is seriously messed up. Return the error
//to the done function to close & remove this client from
//the pool. If you leave a client in the pool with an unaborted
//transaction weird, hard to diagnose problems might happen.
return done(err);
});
};
pg.connect(function(err, client, done) {
if(err) throw err;
client.query('BEGIN', function(err) {
if(err) return rollback(client, done);
//as long as we do not call the `done` callback we can do
//whatever we want...the client is ours until we call `done`
//on the flip side, if you do call `done` before either COMMIT or ROLLBACK
//what you are doing is returning a client back to the pool while it
//is in the middle of a transaction.
//Returning a client while its in the middle of a transaction
//will lead to weird & hard to diagnose errors.
process.nextTick(function() {
var text = 'INSERT INTO account(money) VALUES($1) WHERE id = $2';
client.query(text, [100, 1], function(err) {
if(err) return rollback(client, done);
client.query(text, [-100, 2], function(err) {
if(err) return rollback(client, done);
client.query('COMMIT', done);
});
});
});
});
});
My array logic is:
banking.forEach(function(batch){
client.query(text, [batch.amount, batch.id], function(err, result);
}

pg-promise offers a very flexible support for transactions. See Transactions.
It also supports partial nested transactions, aka savepoints.
The library implements transactions automatically, which is what should be used these days, because too many things can go wrong, if you try organizing a transaction manually as you do in your example.
See a related question: Optional INSERT statement in a transaction

Here's a simple TypeScript solution to avoid pg-promise
import { PoolClient } from "pg"
import { pool } from "../database"
const tx = async (callback: (client: PoolClient) => void) => {
const client = await pool.connect();
try {
await client.query('BEGIN')
try {
await callback(client)
await client.query('COMMIT')
} catch (e) {
await client.query('ROLLBACK')
}
} finally {
client.release()
}
}
export { tx }
Usage:
...
let result;
await tx(async client => {
const { rows } = await client.query<{ cnt: string }>('SELECT COUNT(*) AS cnt FROM users WHERE username = $1', [username]);
result = parseInt(rows[0].cnt) > 0;
});
return result;

Related

MongoError: pool destroyed when fetching all data without conditions

I am new to mongoDb, as I am trying to query from different collection and in order to do that, when I am fetching data from category collection I mean when I am running select * from collection it is throwing error, MongoError: pool destroyed.
As per my understanding it is because of some find({}) is creating a pool and that is being destroyed.
The code which I am using inside model is below,
const MongoClient = require('mongodb').MongoClient;
const dbConfig = require('../configurations/database.config.js');
export const getAllCategoriesApi = (req, res, next) => {
return new Promise((resolve, reject ) => {
let finalCategory = []
const client = new MongoClient(dbConfig.url, { useNewUrlParser: true });
client.connect(err => {
const collection = client.db(dbConfig.db).collection("categories");
debugger
if (err) throw err;
let query = { CAT_PARENT: { $eq: '0' } };
collection.find(query).toArray(function(err, data) {
if(err) return next(err);
finalCategory.push(data);
resolve(finalCategory);
// db.close();
});
client.close();
});
});
}
When my finding here is when I am using
let query = { CAT_PARENT: { $eq: '0' } };
collection.find(query).toArray(function(err, data) {})
When I am using find(query) it is returning data but with {} or $gte/gt it is throwing Pool error.
The code which I have written in controller is below,
import { getAllCategoriesListApi } from '../models/fetchAllCategory';
const redis = require("redis");
const client = redis.createClient(process.env.REDIS_PORT);
export const getAllCategoriesListData = (req, res, next, query) => {
// Try fetching the result from Redis first in case we have it cached
return client.get(`allstorescategory:${query}`, (err, result) => {
// If that key exist in Redis store
if (false) {
res.send(result)
} else {
// Key does not exist in Redis store
getAllCategoriesListApi(req, res, next).then( function ( data ) {
const responseJSON = data;
// Save the Wikipedia API response in Redis store
client.setex(`allstorescategory:${query}`, 3600, JSON.stringify({ source: 'Redis Cache', responseJSON }));
res.send(responseJSON)
}).catch(function (err) {
console.log(err)
})
}
});
}
Can any one tell me what mistake I am doing here. How I can fix pool issue.
Thanking you in advance.
I assume that toArray is asynchronous (i.e. it invokes the callback passed in as results become available, i.e. read from the network).
If this is true the client.close(); call is going to get executed prior to results having been read, hence likely yielding your error.
The close call needs to be done after you have finished iterating the results.
Separately from this, you should probably not be creating the client instance in the request handler like this. Client instances are expensive to create (they must talk to all of the servers in the deployment before they can actually perform queries) and generally should be created per running process rather than per request.

Perform side effects for mongoose/mongodb query

I need to query my database for users based on an array of emails and then execute a function for each result, I do this with eachAsync:
mongoose.model('User')
.find({email: {$in: ['foo#bar.com', 'bar#foo.com']}})
/* -- Run side effects before continuing -- */
.cursor()
.eachAsync((doc) => {
// do stuff
});
The problem I'm having is that I need to return a 404 status if any of the users with the given emails do not exist.
I've been looking through the mongoose docs but I can't seem to find a way of running "side effects" when working with queries. Simply "resolving" the DocumentQuery with .then doesn't work since you can't turn it into a cursor afterwards.
How can I achieve this?
You could try implementing it as shown below. I hope it helps.
// Function using async/await
getCursor: async (_, res) => {
try {
const result = []; // To hold result of cursor
const searchArray = ['foo#bar.com', 'bar#foo.com'];
let hasError = false; // to track error when email from find isn't in the array
const cursor = await mongoose.model('User').find({ email: { $in: searchArray } }).cursor();
// NOTE: Use cursor.on('data') to read the stream of data passed
cursor.on('data', (cursorChunk) => {
// NOTE: Run your side effect before continuing
if (searchArray.indexOf(cursorChunk.email) === -1) {
hasError = true;
res.status(404).json({ message: 'Resource not found!' });
} else {
// Note: Push chunk to result array if you need it
result.push(cursorChunk);
}
});
// NOTE: listen to the cursor.on('end')
cursor.on('end', () => {
// Do stuff or return result to client
if (!hasError) {
res.status(200).json({ result, success: true });
}
});
} catch (error) {
// Do error log and/or return to client
res.status(404).json({ error, message: 'Resource not found!' });
}
}

How to 'pipe' oracle-db data from 'on data' event

I've been using node-oracledb for a few months and I've managed to achieve what I have needed to so far.
I'm currently working on a search app that could potentially return about 2m rows of data from a single call. To ensure I don't get a disconnect from the browser and the server, I thought I would try queryStream so that there is a constant flow of data back to the client.
I implemented the queryStream example as-is, and this worked fine for a few hundred thousand rows. However, when the returned rows is greater than one million, Node runs out of memory. By logging and watching both client and server log events, I can see that client is way behind the server in terms of rows sent and received. So, it looks like Node is falling over because it's buffering so much data.
It's worth noting that at this point, my selectstream implementation is within a req/res function called via Express.
To return the data, I do something like....
stream.on('data', function (data) {
rowcount++;
let obj = new myObjectConstructor(data);
res.write(JSON.stringify(obj.getJson());
});
I've been reading about how streams and pipe can help with flow, so what I'd like to be able to do is to be able to pipe the results from the query to a) help with flow and b) to be able to pipe the results to other functions before sending back to the client.
E.g.
function getData(req, res){
var stream = myQueryStream(connection, query);
stream
.pipe(toSomeOtherFunction)
.pipe(yetAnotherFunction)
.pipe(res);
}
I'm spent a few hours trying to find a solution or example that allows me to pipe results, but I'm stuck and need some help.
Apologies if I'm missing something obvious, but I'm still getting to grips with Node and especially streams.
Thanks in advance.
There's a bit of an impedance mismatch here. The queryStream API emits rows of JavaScript objects, but what you want to stream to the client is a JSON array. You basically have to add an open bracket to the beginning, a comma after each row, and a close bracket to the end.
I'll show you how to do this in a controller that uses the driver directly as you have done, instead of using separate database modules as I advocate in this series.
const oracledb = require('oracledb');
async function get(req, res, next) {
try {
const conn = await oracledb.getConnection();
const stream = await conn.queryStream('select * from employees', [], {outFormat: oracledb.OBJECT});
res.writeHead(200, {'Content-Type': 'application/json'});
res.write('[');
stream.on('data', (row) => {
res.write(JSON.stringify(row));
res.write(',');
});
stream.on('end', () => {
res.end(']');
});
stream.on('close', async () => {
try {
await conn.close();
} catch (err) {
console.log(err);
}
});
stream.on('error', async (err) => {
next(err);
try {
await conn.close();
} catch (err) {
console.log(err);
}
});
} catch (err) {
next(err);
}
}
module.exports.get = get;
Once you get the concepts, you can simplify things a bit with a reusable Transform class which allows you to use pipe in the controller logic:
const oracledb = require('oracledb');
const { Transform } = require('stream');
class ToJSONArray extends Transform {
constructor() {
super({objectMode: true});
this.push('[');
}
_transform (row, encoding, callback) {
if (this._prevRow) {
this.push(JSON.stringify(this._prevRow));
this.push(',');
}
this._prevRow = row;
callback(null);
}
_flush (done) {
if (this._prevRow) {
this.push(JSON.stringify(this._prevRow));
}
this.push(']');
delete this._prevRow;
done();
}
}
async function get(req, res, next) {
try {
const toJSONArray = new ToJSONArray();
const conn = await oracledb.getConnection();
const stream = await conn.queryStream('select * from employees', [], {outFormat: oracledb.OBJECT});
res.writeHead(200, {'Content-Type': 'application/json'});
stream.pipe(toJSONArray).pipe(res);
stream.on('close', async () => {
try {
await conn.close();
} catch (err) {
console.log(err);
}
});
stream.on('error', async (err) => {
next(err);
try {
await conn.close();
} catch (err) {
console.log(err);
}
});
} catch (err) {
next(err);
}
}
module.exports.get = get;
Rather than writing your own logic to create a JSON stream, you can use JSONStream to convert an object stream to (stringified) JSON, before piping it to its destination (res, process.stdout etc) This saves the need to muck around with .on('data',...) events.
In the example below, I've used pipeline from node's stream module rather than the .pipe method: the effect is similar (with better error handling I think). To get objects from oracledb.queryStream, you can specify option {outFormat: oracledb.OUT_FORMAT_OBJECT} (docs). Then you can make arbitrary modifications to the stream of objects produced. This can be done using a transform stream, made perhaps using through2-map, or if you need to drop or split rows, through2. Below the stream is sent to process.stdout after being stringified as JSON, but you could equally send to it express's res.
require('dotenv').config() // config from .env file
const JSONStream = require('JSONStream')
const oracledb = require('oracledb')
const { pipeline } = require('stream')
const map = require('through2-map') // see https://www.npmjs.com/package/through2-map
oracledb.getConnection({
user: process.env.DB_USER,
password: process.env.DB_PASSWORD,
connectString: process.env.CONNECT_STRING
}).then(connection => {
pipeline(
connection.queryStream(`
select dual.*,'test' as col1 from dual
union select dual.*, :someboundvalue as col1 from dual
`
,{"someboundvalue":"test5"} // binds
,{
prefetchRows: 150, // for tuning
fetchArraySize: 150, // for tuning
outFormat: oracledb.OUT_FORMAT_OBJECT
}
)
,map.obj((row,index) => {
row.arbitraryModification = index
return row
})
,JSONStream.stringify() // false gives ndjson
,process.stdout // or send to express's res
,(err) => { if(err) console.error(err) }
)
})
// [
// {"DUMMY":"X","COL1":"test","arbitraryModification":0}
// ,
// {"DUMMY":"X","COL1":"test5","arbitraryModification":1}
// ]

res.send after two forEach have finished executing

const collect = [];
req.body.product.forEach(function(entry) {
mongoClient.connect(databaseServerUrl, function(err, db) {
let testCollection = db.collection('Tests');
testCollection.find({Product: entry}).toArray((err, docs) => {
let waiting = docs.length;
docs.forEach(function (doc) {
collect.push(doc);
finish();
});
function finish() {
waiting--;
if (waiting === 0) {
res.send(collect);
}
}
});
db.close();
});
});
this is only getting back the first set. If I have two nodes in my array of req.body.product for example. I am only getting back the first set. But I need to get back everything not just from one Collection.
Rather than performing two queries and combining the results into one array, I suggest performing a single query that gets all of the results, which would look something like this:
mongoClient.connect(databaseServerUrl, function(err, db) {
const query = { $or: req.body.product.map(Product => ({ Product })) };
db.collection('Tests').find(query).toArray((err, docs) => {
// ...handle `err` here...
res.send(docs);
db.close();
});
});
Note that I haven't tested this since I don't have a MongoDB database in front of me.
your mongoClient.connect() is asyncronous but your loop just execute without waiting for the callback.
Try async forEach loop: enter link description here
This should solve your problem

How to properly return a result from mysql with Node?

In the code
var stuff_i_want = '';
stuff_i_want = get_info(parm);
And the function get_info:
get_info(data){
var sql = "SELECT a from b where info = data"
connection.query(sql, function(err, results){
if (err){
throw err;
}
console.log(results[0].objid); // good
stuff_i_want = results[0].objid; // Scope is larger than function
console.log(stuff_i_want); // Yep. Value assigned..
}
in the larger scope
stuff_i_want = null
What am i missing regarding returning mysql data and assigning it to a variable?
============ New code per Alex suggestion
var parent_id = '';
get_info(data, cb){
var sql = "SELECT a from b where info = data"
connection.query(sql, function(err, results){
if (err){
throw err;
}
return cb(results[0].objid); // Scope is larger than function
}
==== New Code in Use
get_data(parent_recording, function(result){
parent_id = result;
console.log("Parent ID: " + parent_id); // Data is delivered
});
However
console.log("Parent ID: " + parent_id);
In the scope outside the function parent_id is null
You're going to need to get your head around asynchronous calls and callbacks with javascript, this isn't C#, PHP, etc...
Here's an example using your code:
function get_info(data, callback){
var sql = "SELECT a from b where info = data";
connection.query(sql, function(err, results){
if (err){
throw err;
}
console.log(results[0].objid); // good
stuff_i_want = results[0].objid; // Scope is larger than function
return callback(results[0].objid);
})
}
//usage
var stuff_i_want = '';
get_info(parm, function(result){
stuff_i_want = result;
//rest of your code goes in here
});
When you call get_info this, in turn, calls connection.query, which takes a callback (that's what function(err, results) is
The scope is then passed to this callback, and so on.
Welcome to javascript callback hell...
It's easy when you get the hang of it, just takes a bit of getting used to, coming from something like C#
I guess what you really want to do here is returning a Promise object with the results. This way you can deal with the async operation of retrieving data from the DBMS: when you have the results, you make use of the Promise resolve function to somehow "return the value" / "resolve the promise".
Here's an example:
getEmployeeNames = function(){
return new Promise(function(resolve, reject){
connection.query(
"SELECT Name, Surname FROM Employee",
function(err, rows){
if(rows === undefined){
reject(new Error("Error rows is undefined"));
}else{
resolve(rows);
}
}
)}
)}
On the caller side, you use the then function to manage fulfillment, and the catch function to manage rejection.
Here's an example that makes use of the code above:
getEmployeeNames()
.then(function(results){
render(results)
})
.catch(function(err){
console.log("Promise rejection error: "+err);
})
At this point you can set up the view for your results (which are indeed returned as an array of objects):
render = function(results){ for (var i in results) console.log(results[i].Name) }
Edit
I'm adding a basic example on how to return HTML content with the results, which is a more typical scenario for Node. Just use the then function of the promise to set the HTTP response, and open your browser at http://localhost:3001
require('http').createServer( function(req, res){
if(req.method == 'GET'){
if(req.url == '/'){
res.setHeader('Content-type', 'text/html');
getEmployeeNames()
.then(function(results){
html = "<h2>"+results.length+" employees found</h2>"
html += "<ul>"
for (var i in results) html += "<li>" + results[i].Name + " " +results[i].Surname + "</li>";
html += "</ul>"
res.end(html);
})
.catch(function(err){
console.log("Promise rejection error: "+err);
res.end("<h1>ERROR</h1>")
})
}
}
}).listen(3001)
Five years later, I understand asynchronous operations much better.
Also with the new syntax of async/await in ES6 I refactored this particular piece of code:
const mysql = require('mysql2') // built-in promise functionality
const DB = process.env.DATABASE
const conn = mysql.createConnection(DB)
async function getInfo(data){
var sql = "SELECT a from b where info = data"
const results = await conn.promise().query(sql)
return results[0]
}
module.exports = {
getInfo
}
Then, where ever I need this data, I would wrap it in an async function, invoke getInfo(data) and use the results as needed.
This was a situation where I was inserting new records to a child table and needed the prent record key, based only on a name.
This was a good example of understanding the asynchronous nature of node.
I needed to wrap the all the code affecting the child records inside the call to find the parent record id.
I was approaching this from a sequential (PHP, JAVA) perspective, which was all wrong.
Easier if you send in a promise to be resolved
e.g
function get_info(data, promise){
var sql = "SELECT a from b where info = data";
connection.query(sql, function(err, results){
if (err){
throw err;
}
console.log(results[0].objid); // good
stuff_i_want = results[0].objid; // Scope is larger than function
promise.resolve(results[0].objid);
}
}
This way Node.js will stay fast because it's busy doing other things while your promise is waiting to be resolved
I've been working on this goal since few weeks, without any result, and I finally found a way to assign in a variable the result of any mysql query using await/async and promises.
You don't need to understand promises in order to use it, eh, I don't know how to use promises neither anyway
I'm doing it using a Model class for my database like this :
class DB {
constructor(db) {
this.db = db;
}
async getUsers() {
let query = "SELECT * FROM asimov_users";
return this.doQuery(query)
}
async getUserById(array) {
let query = "SELECT * FROM asimov_users WHERE id = ?";
return this.doQueryParams(query, array);
}
// CORE FUNCTIONS DON'T TOUCH
async doQuery(queryToDo) {
let pro = new Promise((resolve,reject) => {
let query = queryToDo;
this.db.query(query, function (err, result) {
if (err) throw err; // GESTION D'ERREURS
resolve(result);
});
})
return pro.then((val) => {
return val;
})
}
async doQueryParams(queryToDo, array) {
let pro = new Promise((resolve,reject) => {
let query = queryToDo;
this.db.query(query, array, function (err, result) {
if (err) throw err; // GESTION D'ERREURS
resolve(result);
});
})
return pro.then((val) => {
return val;
})
}
}
Then, you need to instantiate your class by passing in parameter to constructor the connection variable given by mysql. After this, all you need to do is calling one of your class methods with an await before. With this, you can chain queries without worrying of scopes.
Example :
connection.connect(function(err) {
if (err) throw err;
let DBModel = new DB(connection);
(async function() {
let oneUser = await DBModel.getUserById([1]);
let allUsers = await DBModel.getUsers();
res.render("index.ejs", {oneUser : oneUser, allUsers : allUsers});
})();
});
Notes :
if you need to do another query, you just have to write a new method in your class and calling it in your code with an await inside an async function, just copy/paste a method and modify it
there are two "core functions" in the class, doQuery and doQueryParams, the first one only takes a string as a parameter which basically is your mysql query. The second one is used for parameters in your query, it takes an array of values.
it's relevant to notice that the return value of your methods will always be an array of objects, it means that you'll have to do var[0] if you do a query which returns only one row. In case of multiple rows, just loop on it.

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