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joplin notion extension/Web Development/nodejs/postgresql.md
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joplin notion extension/Web Development/nodejs/postgresql.md
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postgresql
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- Install pg module
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https://node-postgres.com/
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For multiple queries there r 2 methods
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In Node.js, when using the `pg` library (node-postgres) to work with PostgreSQL databases, executing multiple queries consecutively is a common requirement. There are several ways to achieve this depending on the nature of your queries and how they should be executed (e.g., in parallel, in sequence, within a transaction). Below are some approaches:
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#### 1. Sequential Execution (with async/await)
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If your queries are dependent on each other and need to be executed in a sequential manner, you can use `async/await` syntax to execute them one after the other.
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```javascript
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const { Client } = require('pg');
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const client = new Client({
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// Your database connection parameters
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});
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const executeQueriesSequentially = async () => {
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try {
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await client.connect();
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const result1 = await client.query('SELECT * FROM table1;');
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console.log('Result 1:', result1.rows);
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const result2 = await client.query('SELECT * FROM table2;');
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console.log('Result 2:', result2.rows);
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// Continue for more queries
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} catch (err) {
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console.error(err);
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} finally {
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await client.end();
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}
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};
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executeQueriesSequentially();
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```
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#### 2. Parallel Execution
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If your queries are independent of each other, you can execute them in parallel using `Promise.all`.
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```javascript
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const executeQueriesInParallel = async () => {
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try {
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await client.connect();
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const promises = [
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client.query('SELECT * FROM table1;'),
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client.query('SELECT * FROM table2;'),
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// Add more queries as needed
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];
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const results = await Promise.all(promises);
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results.forEach((result, index) => {
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console.log(`Result ${index + 1}:`, result.rows);
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});
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} catch (err) {
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console.error(err);
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} finally {
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await client.end();
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}
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};
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executeQueriesInParallel();
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```
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### 3. Using Transactions
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For cases where your queries must be executed as a single atomic operation, you will want to use a transaction. This is particularly important i
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## Defending from SQL injection
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Also this way will prevent from situation like when we use `insert into tablename values ('${str}')` and if str is `i won't do` then it will like `insert into tablename values ('i won't do)` so strng will be `i won` as later is single quote closing in.
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This method is called parameterized queries or prepared statements instead of manually constructing query strings which handles sql injection and escaping characters.
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- For PostgreSQL (pg package example):
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```js
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const { Pool } = require('pg')
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const pool = new Pool()
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const text = 'INSERT INTO your_table(name) VALUES($1,$2)'
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const values = [`there isn't anything to do`, `ok go`]
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pool.query(text, values, (err, res) => {
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if (err) {
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console.log(err.stack)
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} else {
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console.log(res.rows[0])
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}
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})
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```
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- For MySQL (mysql package example):
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```js
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const mysql = require('mysql');
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const connection = mysql.createConnection({
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host: 'example.org',
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user: 'your_user',
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password: 'your_pass',
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database: 'your_db'
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});
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connection.connect();
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const post = {name: `there isn't anything to do`};
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const query = connection.query('INSERT INTO your_table SET ?', post, (err, result) => {
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if (err) throw err;
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console.log(result);
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});
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connection.end();
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```
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### Reconnecting database
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Sometimes database gets disconnected. There r various ways like reconnecting ir but few things needed to be noted. When reconnecting sometimes we need to create new object too instead of just reconnecting
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Eg:
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```js
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const pg = require("pg");
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let pgClient
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const createPGConnection=()=>{
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pgClient=new pg.Client(conString);
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pgClient.connect()
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console.log('database connected')
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}
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const conString = process.env.CONNECTION_URI;
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client.on("ready", async () => {
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console.log(`Logged in as ${client.user.tag}!`);
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});
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createPGConnection()
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pgClient.on('error',async(err)=>{
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console.log('err: ',err)
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await pgClient.end()
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console.log('connection ended')
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console.log('trying to reconnect')
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await promiseSetTimeOut(5000)
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await createPGConnection()
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})
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```
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**Pooling**
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https://node-postgres.com/features/pooling
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```js
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import pg from "pg";
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const { Pool } = pg;
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const poolConfig = {
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user: process.env.PGUSER,
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password: process.env.PGPASSWORD,
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database: process.env.PGDATABASE,
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host: process.env.PGHOST,
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port: process.env.PGPORT,
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max: 20,
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idleTimeoutMillis: 30000,
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connectionTimeoutMillis: 5000,
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};
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export const pool = new Pool(poolConfig);
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pool.on("error", (error) => {
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console.error("unexpected error on idle client:", error.message);
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process.exit(1);
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});
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export const query = (text, params) => pool.query(text, params);
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```
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some testing
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```js
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const test = async () => {
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try {
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await query("SELECT 1");
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console.log("database connected bro.");
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return true;
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} catch (err) {
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}
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};
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```
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transactions
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```js
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import { Pool } from 'pg'
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const pool = new Pool()
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const client = await pool.connect()
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try {
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await client.query('BEGIN')
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const queryText = 'INSERT INTO users(name) VALUES($1) RETURNING id'
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const res = await client.query(queryText, ['brianc'])
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const insertPhotoText = 'INSERT INTO photos(user_id, photo_url) VALUES ($1, $2)'
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const insertPhotoValues = [res.rows[0].id, 's3.bucket.foo']
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await client.query(insertPhotoText, insertPhotoValues)
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await client.query('COMMIT')
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} catch (e) {
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await client.query('ROLLBACK')
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throw e
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} finally {
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client.release()
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}
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```
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