This tutorial shows you how build a simple Node.js application with CockroachDB and the node-postgres driver.
Step 1. Start CockroachDB
Create a free cluster
Organizations without billing information on file can only create one CockroachDB Serverless cluster.
- If you haven't already, sign up for a CockroachDB Cloud account.
- Log in to your CockroachDB Cloud account.
- On the Clusters page, click Create Cluster.
- On the Select a plan page, select Serverless.
- On the Cloud & Regions page, select a cloud provider (GCP or AWS) in the Cloud provider section.
- In the Regions section, select a region for the cluster. Refer to CockroachDB Cloud Regions for the regions where CockroachDB Serverless clusters can be deployed. To create a multi-region cluster, click Add region and select additional regions. A cluster can have at most six regions.
- Click Next: Capacity.
- On the Capacity page, select Start for free. Click Next: Finalize.
On the Finalize page, click Create cluster.
Your cluster will be created in a few seconds and the Create SQL user dialog will display.
Set up your cluster connection
Navigate to the cluster's Overview page, and select Connect.
Under the Connection String tab, download the cluster certificate.
Take note of the connection string provided. You'll use it to connect to the database later in this tutorial.
- If you haven't already, download the CockroachDB binary.
Run the
cockroach start-single-node
command:$ cockroach start-single-node --advertise-addr 'localhost' --insecure
This starts an insecure, single-node cluster.
Take note of the following connection information in the SQL shell welcome text:
CockroachDB node starting at 2021-08-30 17:25:30.06524 +0000 UTC (took 4.3s) build: CCL v21.1.6 @ 2021/07/20 15:33:43 (go1.15.11) webui: http://localhost:8080 sql: postgresql://root@localhost:26257?sslmode=disable
You'll use the
sql
connection string to connect to the cluster later in this tutorial.
The --insecure
flag used in this tutorial is intended for non-production testing only. To run CockroachDB in production, use a secure cluster instead.
Step 2. Get the code
Clone the code's GitHub repo:
$ git clone https://github.com/cockroachlabs/example-app-node-postgres
The project has the following directory structure:
├── README.md
├── app.js
├── dbinit.sql
└── package.json
The dbinit.sql
file initializes the database schema that the application uses:
CREATE TABLE accounts (
id UUID PRIMARY KEY,
balance INT8
);
The app.js
file contains the code for INSERT
, SELECT
, UPDATE
, and DELETE
SQL operations:
const { Pool } = require("pg");
const { v4: uuidv4 } = require("uuid");
var accountValues = Array(3);
// Wrapper for a transaction. This automatically re-calls the operation with
// the client as an argument as long as the database server asks for
// the transaction to be retried.
async function retryTxn(n, max, client, operation, callback) {
const backoffInterval = 100; // millis
const maxTries = 5;
let tries = 0;
while (true) {
await client.query('BEGIN;');
tries++;
try {
const result = await operation(client, callback);
await client.query('COMMIT;');
return result;
} catch (err) {
await client.query('ROLLBACK;');
if (err.code !== '40001' || tries == maxTries) {
throw err;
} else {
console.log('Transaction failed. Retrying.');
console.log(err.message);
await new Promise(r => setTimeout(r, tries * backoffInterval));
}
}
}
}
// This function is called within the first transaction. It inserts some initial values into the "accounts" table.
async function initTable(client, callback) {
let i = 0;
while (i < accountValues.length) {
accountValues[i] = await uuidv4();
i++;
}
const insertStatement =
"INSERT INTO accounts (id, balance) VALUES ($1, 1000), ($2, 250), ($3, 0);";
await client.query(insertStatement, accountValues, callback);
const selectBalanceStatement = "SELECT id, balance FROM accounts;";
await client.query(selectBalanceStatement, callback);
}
// This function updates the values of two rows, simulating a "transfer" of funds.
async function transferFunds(client, callback) {
const from = accountValues[0];
const to = accountValues[1];
const amount = 100;
const selectFromBalanceStatement =
"SELECT balance FROM accounts WHERE id = $1;";
const selectFromValues = [from];
await client.query(
selectFromBalanceStatement,
selectFromValues,
(err, res) => {
if (err) {
return callback(err);
} else if (res.rows.length === 0) {
console.log("account not found in table");
return callback(err);
}
var acctBal = res.rows[0].balance;
if (acctBal < amount) {
return callback(new Error("insufficient funds"));
}
}
);
const updateFromBalanceStatement =
"UPDATE accounts SET balance = balance - $1 WHERE id = $2;";
const updateFromValues = [amount, from];
await client.query(updateFromBalanceStatement, updateFromValues, callback);
const updateToBalanceStatement =
"UPDATE accounts SET balance = balance + $1 WHERE id = $2;";
const updateToValues = [amount, to];
await client.query(updateToBalanceStatement, updateToValues, callback);
const selectBalanceStatement = "SELECT id, balance FROM accounts;";
await client.query(selectBalanceStatement, callback);
}
// This function deletes the third row in the accounts table.
async function deleteAccounts(client, callback) {
const deleteStatement = "DELETE FROM accounts WHERE id = $1;";
await client.query(deleteStatement, [accountValues[2]], callback);
const selectBalanceStatement = "SELECT id, balance FROM accounts;";
await client.query(selectBalanceStatement, callback);
}
// Run the transactions in the connection pool
(async () => {
const connectionString = process.env.DATABASE_URL;
const pool = new Pool({
connectionString,
application_name: "$ docs_simplecrud_node-postgres",
});
// Connect to database
const client = await pool.connect();
// Callback
function cb(err, res) {
if (err) throw err;
if (res.rows.length > 0) {
console.log("New account balances:");
res.rows.forEach((row) => {
console.log(row);
});
}
}
// Initialize table in transaction retry wrapper
console.log("Initializing accounts table...");
await retryTxn(0, 15, client, initTable, cb);
// Transfer funds in transaction retry wrapper
console.log("Transferring funds...");
await retryTxn(0, 15, client, transferFunds, cb);
// Delete a row in transaction retry wrapper
console.log("Deleting a row...");
await retryTxn(0, 15, client, deleteAccounts, cb);
// Exit program
process.exit();
})().catch((err) => console.log(err.stack));
All of the database operations are wrapped in a helper function named retryTxn
. This function attempts to commit statements in the context of an explicit transaction. If a retry error is thrown, the wrapper will retry committing the transaction, with exponential backoff, until the maximum number of retries is reached (by default, 15).
Step 3. Initialize the database
To initialize the example database, use the cockroach sql
command to execute the SQL statements in the dbinit.sql
file:
cat dbinit.sql | cockroach sql --url "<connection-string>"
Where <connection-string>
is the connection string you obtained earlier from the CockroachDB Cloud Console.
cat dbinit.sql | cockroach sql --url "postgresql://root@localhost:26257?sslmode=disable"
postgresql://root@localhost:26257?sslmode=disable
is the sql
connection string you obtained earlier from the cockroach
welcome text.
The SQL statements in the initialization file should execute:
SET
Time: 1ms
SET
Time: 2ms
DROP DATABASE
Time: 1ms
CREATE DATABASE
Time: 2ms
SET
Time: 10ms
CREATE TABLE
Time: 4ms
Step 4. Run the code
Install the app requirements:
$ npm install
Run the app:
$ node app.js
The program will prompt you for a connection string to the database:
prompt: connectionString:
Enter the connection string to your running cluster.
Tip:postgresql://root@localhost:26257?sslmode=disable
should be thesql
connection URL provided in thecockroach
welcome text.Tip:Use the connection string provided in the Connection info window of the CockroachDB Cloud Console.
Note:You need to provide a SQL user password in order to securely connect to a CockroachDB Cloud cluster. The connection string should have a placeholder for the password (
<ENTER-PASSWORD>
).
After entering the connection string, the program will execute.
The output should look like this:
Initializing accounts table...
New account balances:
{ id: 'aa0e9b22-0c23-469b-a9e1-b2ace079f44c', balance: '1000' }
{ id: 'bf8b96da-2c38-4d55-89a0-b2b6ed63ff9e', balance: '0' }
{ id: 'e43d76d6-388e-4ee6-8b73-a063a63a2138', balance: '250' }
Transferring funds...
New account balances:
{ id: 'aa0e9b22-0c23-469b-a9e1-b2ace079f44c', balance: '900' }
{ id: 'bf8b96da-2c38-4d55-89a0-b2b6ed63ff9e', balance: '0' }
{ id: 'e43d76d6-388e-4ee6-8b73-a063a63a2138', balance: '350' }
Deleting a row...
New account balances:
{ id: 'aa0e9b22-0c23-469b-a9e1-b2ace079f44c', balance: '900' }
{ id: 'e43d76d6-388e-4ee6-8b73-a063a63a2138', balance: '350' }
What's next?
Read more about using the node-postgres driver.
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