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

Before You Begin

Make sure you have already installed CockroachDB.

Step 1. Install the Go pq driver

To install the Go pq driver, run the following command:

$ go get -u github.com/lib/pq

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 --background \
--store=hello-1

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 --background \
--store=hello-2 \
--port=26258 \
--http-port=8081 \
--join=localhost:26257

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

Step 3. Create a user

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

$ cockroach user set maxroach

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 -e 'CREATE DATABASE bank'

Then grant privileges to the maxroach user

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

Step 5. Run the Go code

Basic Statements

The following code connects as the maxroach user and executes some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.

Copy the code or download it directly.

package main

import (
	"database/sql"
	"fmt"
	"log"

	_ "github.com/lib/pq"
)

func main() {
	// Connect to the "bank" database.
	db, err := sql.Open("postgres", "postgresql:[email protected]:26257/bank?sslmode=disable")
	if err != nil {
		log.Fatalf("error connection to the database: %s", err)
	}

	// Create the "accounts" table.
	if _, err := db.Exec(
		"CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)"); err != nil {
		log.Fatal(err)
	}

	// Insert two rows into the "accounts" table.
	if _, err := db.Exec(
		"INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)"); err != nil {
		log.Fatal(err)
	}

	// Print out the balances.
	rows, err := db.Query("SELECT id, balance FROM accounts")
	if err != nil {
		log.Fatal(err)
	}
	defer rows.Close()
	fmt.Println("Initial balances:")
	for rows.Next() {
		var id, balance int
		if err := rows.Scan(&id, &balance); err != nil {
			log.Fatal(err)
		}
		fmt.Printf("%d %d\n", id, balance)
	}
}

Then run the code:

$ go run basic-sample.go

The output should be:

Initial balances:
1 1000
2 250

Transaction (with retry logic)

The following code again connects as the maxroach user but this time executes 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.

package main

import (
	"database/sql"
	"fmt"
	"log"

	"github.com/cockroachdb/cockroach-go/crdb"
)

func transferFunds(tx *sql.Tx, from int, to int, amount int) error {
	// Read the balance.
	var fromBalance int
	if err := tx.QueryRow(
		"SELECT balance FROM accounts WHERE id = $1", from).Scan(&fromBalance); err != nil {
		return err
	}

	if fromBalance < amount {
		return fmt.Errorf("insufficient funds")
	}

	// Perform the transfer.
	if _, err := tx.Exec(
		"UPDATE accounts SET balance = balance - $1 WHERE id = $2", amount, from); err != nil {
		return err
	}
	if _, err := tx.Exec(
		"UPDATE accounts SET balance = balance + $1 WHERE id = $2", amount, to); err != nil {
		return err
	}
	return nil
}

func main() {
	db, err := sql.Open("postgres", "postgresql:[email protected]:26257/bank?sslmode=disable")
	if err != nil {
		log.Fatal("error connection to the database: ", err)
	}

	// Run a transfer in a transaction.
	err = crdb.ExecuteTx(db, func(tx *sql.Tx) error {
		return transferFunds(tx, 1 /* from acct# */, 2 /* to acct# */, 100 /* amount */)
	})
	if err == nil {
		fmt.Println("Success")
	} else {
		log.Fatalf("error: %s", err)
	}
}

Because the CockroachDB transaction model requires the client to initiate retries in the case of contention, CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. For Go, the CockroachDB retry function is in the crdb package of the CockroachDB Go client. Clone the library into your $GOPATH as follows:

$ mkdir -p $GOPATH/github.com/cockroachdb
$ cd $GOPATH/github.com/cockroachdb
$ git clone [email protected]:cockroachdb/cockroach-go.git

Then run the code:

$ go run txn-sample.go

The output should just be:

Success

However, if you want to verify that funds were, in fact, transferred from one account to another, you can again use the built-in SQL client:

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

What’s Next?

Read more about using the Go pq driver.

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



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