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

Before you begin

  1. Install CockroachDB.
  2. Start up a secure or insecure local cluster.
  3. Choose the instructions that correspond to whether your cluster is secure or insecure:

Step 1. Install the pgx driver

To install the pgx driver, run the following command:

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$ go get -u github.com/jackc/pgx

Step 2. Install the CockroachDB Go library

To install the CockroachDB Go library, run the following command:

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$ go get -u github.com/cockroachdb/cockroach-go/crdb

Step 3. Create the maxroach user and bank database

Start the built-in SQL shell:

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$ cockroach sql --certs-dir=certs

In the SQL shell, issue the following statements to create the maxroach user and bank database:

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> CREATE USER IF NOT EXISTS maxroach;
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> CREATE DATABASE bank;

Give the maxroach user the necessary permissions:

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> GRANT ALL ON DATABASE bank TO maxroach;

Exit the SQL shell:

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> \q

Step 4. Generate a certificate for the maxroach user

Create a certificate and key for the maxroach user by running the following command:

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$ cockroach cert create-client maxroach --certs-dir=certs --ca-key=my-safe-directory/ca.key

The code samples will run with maxroach as the user.

Step 5. Run the Go 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.

Tip:

To clone a version of the code below that connects to insecure clusters, run the following:

git clone https://github.com/cockroachlabs/hello-world-go-pgx/

Note that you will need to edit the connection string to use the certificates that you generated when you set up your secure cluster.

Basic statements

First, use the following code to connect to the cluster as the maxroach user, and then execute some basic SQL statements that create a table, insert some rows, and read and print the rows to the console.

Download the basic-sample-pgx.go file, or create the file yourself and copy the code into it.

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package main

import (
    "context"
    "fmt"
    "log"

    "github.com/jackc/pgx/v4"
)

func main() {
    config, err := pgx.ParseConfig("postgresql://maxroach@localhost:26257/bank?sslmode=require&sslrootcert=certs/ca.crt&sslkey=certs/client.maxroach.key&sslcert=certs/client.maxroach.crt")
    if err != nil {
        log.Fatal("error configuring the database: ", err)
    }

    config.TLSConfig.ServerName = "localhost"

    // Connect to the "bank" database.
    conn, err := pgx.ConnectConfig(context.Background(), config)
    if err != nil {
        log.Fatal("error connecting to the database: ", err)
    }
    defer conn.Close(context.Background())

    // Create the "accounts" table.
    if _, err := conn.Exec(context.Background(),
        "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 := conn.Exec(context.Background(),
        "INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)"); err != nil {
        log.Fatal(err)
    }

    // Print out the balances.
    rows, err := conn.Query(context.Background(), "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)
    }
}

Initialize the module:

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$ go mod init basic-sample-pgx

Then run the code:

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$ go run basic-sample-pgx.go

The output should be:

Initial balances:
1 1000
2 250

Transaction (with retry logic)

Next, use the following code to connect as maxroach user, and then execute a batch of statements as an atomic transaction to transfer funds from one account to another. All statements in the transaction are either committed or aborted.

Download the txn-sample-pgx.go file, or create the file yourself and copy the code into it.

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package main

import (
    "context"
    "fmt"
    "log"

    "github.com/cockroachdb/cockroach-go/crdb/crdbpgx"
    "github.com/jackc/pgx/v4"
)

func transferFunds(ctx context.Context, tx pgx.Tx, from int, to int, amount int) error {
    // Read the balance.
    var fromBalance int
    if err := tx.QueryRow(ctx,
        "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(ctx,
        "UPDATE accounts SET balance = balance - $1 WHERE id = $2", amount, from); err != nil {
        return err
    }
    if _, err := tx.Exec(ctx,
        "UPDATE accounts SET balance = balance + $1 WHERE id = $2", amount, to); err != nil {
        return err
    }
    return nil
}

func main() {
    config, err := pgx.ParseConfig("postgresql://maxroach@localhost:26257/bank?sslmode=require&sslrootcert=certs/ca.crt&sslkey=certs/client.maxroach.key&sslcert=certs/client.maxroach.crt")
    if err != nil {
        log.Fatal("error configuring the database: ", err)
    }

    config.TLSConfig.ServerName = "localhost"

    // Connect to the "bank" database.
    conn, err := pgx.ConnectConfig(context.Background(), config)
    if err != nil {
        log.Fatal("error connecting to the database: ", err)
    }
    defer conn.Close(context.Background())

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

CockroachDB may require the client to retry a transaction in 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.

To run the code:

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$ go run txn-sample-pgx.go

The output should be:

Success

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

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

Step 3. Create the maxroach user and bank database

Start the built-in SQL shell:

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$ cockroach sql --insecure

In the SQL shell, issue the following statements to create the maxroach user and bank database:

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> CREATE USER IF NOT EXISTS maxroach;
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> CREATE DATABASE bank;

Give the maxroach user the necessary permissions:

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> GRANT ALL ON DATABASE bank TO maxroach;

Exit the SQL shell:

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> \q

Step 4. Run the Go 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.

Tip:

To clone a version of the code below that connects to insecure clusters, run the following:

git clone https://github.com/cockroachlabs/hello-world-go-pgx/

Note that you will need to edit the connection string to use the certificates that you generated when you set up your secure cluster.

Basic statements

First, use the following code to connect to the cluster as the maxroach user, and then execute some basic SQL statements that create a table, insert some rows, and read and print the rows to the console.

Download the basic-sample-pgx.go file, or create the file yourself and copy the code into it.

copy
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package main

import (
    "context"
    "fmt"
    "log"

    "github.com/jackc/pgx/v4"
)

func main() {
    config, err := pgx.ParseConfig("postgresql://maxroach@localhost:26257/bank?sslmode=disable")
    if err != nil {
        log.Fatal("error configuring the database: ", err)
    }

    // Connect to the "bank" database.
    conn, err := pgx.ConnectConfig(context.Background(), config)
    if err != nil {
        log.Fatal("error connecting to the database: ", err)
    }
    defer conn.Close(context.Background())

    // Create the "accounts" table.
    if _, err := conn.Exec(context.Background(),
        "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 := conn.Exec(context.Background(),
        "INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)"); err != nil {
        log.Fatal(err)
    }

    // Print out the balances.
    rows, err := conn.Query(context.Background(), "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)
    }
}

Initialize the module:

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$ go mod init basic-sample-pgx

Then run the code:

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$ go run basic-sample-pgx.go

The output should be:

Initial balances:
1 1000
2 250

Transaction (with retry logic)

Next, use the following code to connect as maxroach user, and then execute a batch of statements as an atomic transaction to transfer funds from one account to another. All statements in the transaction are either committed or aborted.

Download the txn-sample-pgx.go file, or create the file yourself and copy the code into it.

copy
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package main

import (
    "context"
    "fmt"
    "log"

    "github.com/cockroachdb/cockroach-go/crdb/crdbpgx"
    "github.com/jackc/pgx/v4"
)

func transferFunds(ctx context.Context, tx pgx.Tx, from int, to int, amount int) error {
    // Read the balance.
    var fromBalance int
    if err := tx.QueryRow(ctx,
        "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(ctx,
        "UPDATE accounts SET balance = balance - $1 WHERE id = $2", amount, from); err != nil {
        return err
    }
    if _, err := tx.Exec(ctx,
        "UPDATE accounts SET balance = balance + $1 WHERE id = $2", amount, to); err != nil {
        return err
    }
    return nil
}

func main() {
    config, err := pgx.ParseConfig("postgresql://maxroach@localhost:26257/bank?sslmode=disable")
    if err != nil {
        log.Fatal("error configuring the database: ", err)
    }

    // Connect to the "bank" database.
    conn, err := pgx.ConnectConfig(context.Background(), config)
    if err != nil {
        log.Fatal("error connecting to the database: ", err)
    }
    defer conn.Close(context.Background())

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

CockroachDB may require the client to retry a transaction in 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.

To run the code:

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$ go run txn-sample-pgx.go

The output should be:

Success

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

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$ 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 Go pgx driver.

You might also be interested in the following pages:



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