This tutorial shows you how build a simple Ruby application with CockroachDB using a PostgreSQL-compatible driver or ORM. We’ve tested and can recommend the Ruby pg driver and the ActiveRecord ORM, so those are featured here.

Before You Begin

Make sure you have already installed CockroachDB.

Step 1. Install the Ruby pg driver

To install the Ruby pg driver, run the following command:

$ gem install pg

Step 2. Start a cluster

For the purpose of this tutorial, you need only one CockroachDB node running in insecure mode:

# Start node 1:
$ cockroach start --insecure \
--store=hello-1 \
--host=localhost \
--background

But as you might’ve seen in the Start a Local Cluster tutorial, it’s incredibly easy to start and join addition nodes, if you want to simulate a real cluster:

# Start node 2:
$ cockroach start --insecure \
--store=hello-2 \
--host=localhost \
--port=26258 \
--http-port=8081 \
--join=localhost:26257 \
--background

# Start node 3:
$ cockroach start --insecure \
--store=hello-3 \
--host=localhost \
--port=26259 \
--http-port=8082 \
--join=localhost:26257 \
--background

Step 3. Create a user

As the root user, use the cockroach user command to create a new user, maxroach.

$ cockroach user set maxroach --insecure

Step 4. Create a database and grant privileges

As the root user, use the built-in SQL client to create a bank database.

$ cockroach sql --insecure -e 'CREATE DATABASE bank'

Then grant privileges to the maxroach user

$ cockroach sql --insecure -e 'GRANT ALL ON DATABASE bank TO maxroach'

Step 5. Run the Ruby code

Now that you have a database and a user, you’ll run code to create a table and insert some rows, and then you’ll run code to read and update values as an atomic transaction.

Basic Statements

First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.

Copy the code or download it directly.

# Import the driver.
require 'pg'

# Connect to the "bank" database.
conn = PG.connect(user: 'maxroach', dbname: 'bank', host: 'localhost', port: 26257)

# Create the "accounts" table.
conn.exec('CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)')

# Insert two rows into the "accounts" table.
conn.exec('INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)')

# Print out the balances.
puts 'Initial balances:'
conn.exec('SELECT id, balance FROM accounts') do |res|
  res.each do |row|
    puts row
  end
end

# Close communication with the database.
conn.close()

Then run the code:

$ ruby basic-sample.rb

The output should be:

Initial balances:
{"id"=>"1", "balance"=>"1000"}
{"id"=>"2", "balance"=>"250"}

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

Copy the code or download it directly.

With the default SERIALIZABLE isolation level, CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code.
# Import the driver.
require 'pg'

# Wrapper for a transaction.
# This automatically re-calls "op" with the open transaction as an argument
# as long as the database server asks for the transaction to be retried.
def run_transaction(conn)
  conn.transaction do |txn|
    txn.exec('SAVEPOINT cockroach_restart')
    while
      begin
        # Attempt the work.
        yield txn

        # If we reach this point, commit.
        txn.exec('RELEASE SAVEPOINT cockroach_restart')
        break
      rescue PG::TRSerializationFailure
        txn.exec('ROLLBACK TO SAVEPOINT cockroach_restart')
      end
    end
  end
end

def transfer_funds(txn, from, to, amount)
  txn.exec_params('SELECT balance FROM accounts WHERE id = $1', [from]) do |res|
    res.each do |row|
      raise 'insufficient funds' if Integer(row['balance']) < amount
    end
  end
  txn.exec_params('UPDATE accounts SET balance = balance - $1 WHERE id = $2', [amount, from])
  txn.exec_params('UPDATE accounts SET balance = balance + $1 WHERE id = $2', [amount, to])
end

# Connect to the "bank" database.
conn = PG.connect(user: 'maxroach', dbname: 'bank', host: 'localhost', port: 26257)

run_transaction(conn) do |txn|
  transfer_funds(txn, 1, 2, 100)
end

# Close communication with the database.
conn.close()

Then run the code:

$ ruby txn-sample.rb

To verify that funds were transferred from one account to another, use the built-in SQL client:

$ cockroach sql --insecure -e 'SELECT id, balance FROM accounts' --database=bank
+----+---------+
| id | balance |
+----+---------+
|  1 |     900 |
|  2 |     350 |
+----+---------+
(2 rows)

What’s Next?

Read more about using the Ruby pg driver.

You might also be interested in using a local cluster to explore the following core CockroachDB features:



Yes No