Build a Go App with CockroachDB the Go pq Driver

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This tutorial shows you how build a simple Go application with CockroachDB and the Go pq driver.

Step 1. Start CockroachDB

Choose whether to run a temporary local cluster or a free CockroachDB cluster on CockroachDB Serverless. The instructions below will adjust accordingly.

Create a free cluster

Note:

Organizations without billing information on file can only create one CockroachDB Basic 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 Basic.
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 Basic clusters can be deployed. To create a multi-region cluster, click Add region and select additional 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

Once your cluster is created, the Connect to cluster-name dialog displays. Use the information provided in the dialog to set up your cluster connection for the SQL user that was created by default:

In your terminal, run the second command from the dialog to create a new certs directory on your local machine and download the CA certificate to that directory:
```
curl --create-dirs -o ~/.postgresql/root.crt -O https://cockroachlabs.cloud/clusters/{cluster-id}/cert
```
Your cert file will be downloaded to ~/.postgresql/root.crt.
```
curl --create-dirs -o ~/.postgresql/root.crt -O https://cockroachlabs.cloud/clusters/{cluster-id}/cert
```
Your cert file will be downloaded to ~/.postgresql/root.crt.
```
mkdir -p $env:appdata\.postgresql\; Invoke-WebRequest -Uri https://cockroachlabs.cloud/clusters/{cluster-id}/cert -OutFile $env:appdata\.postgresql\root.crt
```
Your cert file will be downloaded to %APPDATA%/.postgresql/root.crt.
Copy the connection string provided, which will be used in the next steps (and to connect to your cluster in the future).

Warning:

This connection string contains your password, which will be provided only once. If you forget your password, you can reset it by going to the SQL Users page for the cluster, found at https://cockroachlabs.cloud/cluster/<CLUSTER ID>/users.
```
cockroach sql --url 'postgresql://<username>:<password>@<cluster-host>:26257/defaultdb?sslmode=verify-full&sslrootcert='$HOME'/.postgresql/root.crt'
```
```
cockroach sql --url 'postgresql://<username>:<password>@<cluster-host>:26257/defaultdb?sslmode=verify-full&sslrootcert='$HOME'/.postgresql/root.crt'
```
```
cockroach sql --url "postgresql://<username>:<password>@<cluster-host>:26257/defaultdb?sslmode=verify-full&sslrootcert=$env:appdata/.postgresql/root.crt"
```
Where:
- <username> is the SQL user. By default, this is your CockroachDB Cloud account username.
- <password> is the password for the SQL user. The password will be shown only once in the Connection info dialog after creating the cluster.
- <cluster-hostname> is the hostname of your CockroachDB Cloud cluster.
- <cluster-id> is a unique string used to identify your cluster when downloading the CA certificate. For example, 12a3bcde-4fa5-6789-1234-56bc7890d123.
You can find these settings in the Connection parameters tab of the Connection info dialog.

If you haven't already, download the CockroachDB binary.
Run the cockroach demo command:
```
$ cockroach demo \
--no-example-database
```
This starts a temporary, in-memory cluster and opens an interactive SQL shell to the cluster. Any changes to the database will not persist after the cluster is stopped.

Note:

If cockroach demo fails due to SSL authentication, make sure you have cleared any previously downloaded CA certificates from the directory ~/.postgresql.

Take note of the (sql) connection string in the SQL shell welcome text:

# Connection parameters:
#   (webui)    http://127.0.0.1:8080/demologin?password=demo76950&username=demo
#   (sql)      postgres://demo:demo76950@127.0.0.1:26257?sslmode=require
#   (sql/unix) postgres://demo:demo76950@?host=%2Fvar%2Ffolders%2Fc8%2Fb_q93vjj0ybfz0fz0z8vy9zc0000gp%2FT%2Fdemo070856957&port=26257

Step 2. Create a database

In the SQL shell, create the bank database that your application will use:
```
> CREATE DATABASE bank;
```
Create a SQL user for your app:
```
> CREATE USER <username> WITH PASSWORD <password>;
```
Take note of the username and password. You will use it in your application code later.
Give the user the necessary permissions:
```
> GRANT ALL ON DATABASE bank TO <username>;
```

If you haven't already, download the CockroachDB binary.
Start the built-in SQL shell using the connection string you got from the CockroachDB Cloud Console earlier:
```
$ cockroach sql \
--url='postgres://<username>:<password>@<global host>:26257/<cluster_name>.defaultdb?sslmode=verify-full&sslrootcert=<certs_dir>/cc-ca.crt'
```
In the connection string copied from the CockroachDB Cloud Console, your username, password and cluster name are pre-populated. Replace the <certs_dir> placeholder with the path to the certs directory that you created earlier.
In the SQL shell, create the bank database that your application will use:
```
> CREATE DATABASE bank;
```
Exit the SQL shell:
```
> \q
```

Step 3. Run the Go code

You can now run the code sample (main.go) provided in this tutorial to do the following:

Create a table in the bank database.
Insert some rows into the table you created.
Read values from the table.
Execute a batch of statements as an atomic transaction.

Note that CockroachDB may require the client to retry a transaction in the case of read/write contention. The CockroachDB Go client includes a generic retry function (ExecuteTx()) that runs inside a transaction and retries it as needed. The code sample shows how you can use this function to wrap SQL statements.

Get the code

You can copy the code below, download the code directly, or clone the code's GitHub repository.

Here are the contents of main.go:

package main

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

    "github.com/cockroachdb/cockroach-go/crdb"
    _ "github.com/lib/pq"
)

func printBalances(db *sql.DB) {
    // Print out the balances.
    rows, err := db.Query("SELECT id, balance FROM accounts")
    if err != nil {
        log.Fatal(err)
    }
    defer rows.Close()
    fmt.Println("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)
    }
}

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", os.Getenv("DATABASE_URL")+"&application_name=$ docs_simplecrud_gopq")
    if err != nil {
        log.Fatal(err)
    }
    defer db.Close()

    // 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 before an account transfer (below).
    printBalances(db)

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

    // Print out the balances after an account transfer.
    printBalances(db)
}

Update the connection parameters

Edit the connection string passed to sql.Open() so that:

{username} and {password} specify the SQL username and password that you created earlier.
{hostname} and {port} specify the hostname and port in the (sql) connection string from SQL shell welcome text.

Replace the string passed to sql.Open() with the connection string that you copied earlier from the Connection info dialog.

The function call should look similar to the following:

db, err := sql.Open("postgres", "postgresql://{user}:{password}@{globalhost}:26257/bank?sslmode=verify-full&sslrootcert={path to the CA certificate}&options=--cluster={cluster_name}")

Where:

{username} and {password} specify the SQL username and password that you created earlier.
{globalhost} is the name of the Serverless host (e.g., free-tier.gcp-us-central1.cockroachlabs.cloud).
{path to the CA certificate} is the path to the cc-ca.crt file that you downloaded from the CockroachDB Cloud Console.
{cluster_name} is the name of your cluster.

Note:

If you are using the connection string that you copied from the Connection info modal, your username, password, hostname, and cluster name will be pre-populated.

Run the code

Initialize the module:

$ go mod init basic-sample

Then run the code:

$ go run main.go

The output should be:

Balances:
1 1000
2 250
Success
Balances:
1 900
2 350

To verify that the SQL statements were executed, run the following query from inside the SQL shell:

> USE bank;

> SELECT id, balance FROM accounts;

The output should be:

  id | balance
-----+----------
   1 |     900
   2 |     350
(2 rows)

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