Build a Go App with CockroachDB and upper/db

This tutorial shows you how build a simple Go application with CockroachDB and the upper/db data access layer.

Before you begin

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

Step 1. Create the maxroach user and bank database

Start the :

$ cockroach sql --certs-dir=certs

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

> CREATE USER IF NOT EXISTS maxroach;

> CREATE DATABASE bank;

Give the maxroach user the necessary permissions:

> GRANT ALL ON DATABASE bank TO maxroach;

Exit the SQL shell:

> \q

Step 2. Generate a certificate for the maxroach user

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

$ 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 3. Run the Go code

The sample code shown below uses upper/db to map Go-specific objects to SQL operations. Specifically, the code:

• Creates the accounts table, if it does not already exist.
• Deletes any existing rows in the accounts table.
• Inserts two rows into the accounts table.
• Prints the rows in the accounts table to the terminal.
• Deletes the first row in the accounts table.
• Updates the rows in the accounts table within an explicit .
• Prints the rows in the accounts table to the terminal once more.

package main

    "fmt"
    "log"
    "time"

    "github.com/upper/db/v4"
    "github.com/upper/db/v4/adapter/cockroachdb"
)

// The settings variable stores connection details.
var settings = cockroachdb.ConnectionURL{
    Host:     "localhost",
    Database: "bank",
    User:     "maxroach",
    Options: map[string]string{
        // Secure node.
         "sslrootcert": "certs/ca.crt",
         "sslkey":      "certs/client.maxroach.key",
         "sslcert":     "certs/client.maxroach.crt",
    },
}

// Accounts is a handy way to represent a collection.
func Accounts(sess db.Session) db.Store {
    return sess.Collection("accounts")
}

// Account is used to represent a single record in the "accounts" table.
type Account struct {
    ID      uint64 `db:"id,omitempty"`
    Balance int64  `db:"balance"`
}

// Collection is required in order to create a relation between the Account
// struct and the "accounts" table.
func (a *Account) Store(sess db.Session) db.Store {
    return Accounts(sess)
}

// createTables creates all the tables that are neccessary to run this example.
func createTables(sess db.Session) error {
    _, err := sess.SQL().Exec(`
        CREATE TABLE IF NOT EXISTS accounts (
            ID SERIAL PRIMARY KEY,
            balance INT
        )
    `)
    if err != nil {
        return err
    }
    return nil
}

// crdbForceRetry can be used to simulate a transaction error and
// demonstrate upper/db's ability to retry the transaction automatically.
//
// By default, upper/db will retry the transaction five times, if you want
// to modify this number use: sess.SetMaxTransactionRetries(n).
//
// This is only used for demonstration purposes and not intended
// for production code.
func crdbForceRetry(sess db.Session) error {
    var err error

    // The first statement in a transaction can be retried transparently on the
    // server, so we need to add a placeholder statement so that our
    // force_retry() statement isn't the first one.
    _, err = sess.SQL().Exec(`SELECT 1`)
    if err != nil {
        return err
    }

    // If force_retry is called during the specified interval from the beginning
    // of the transaction it returns a retryable error. If not, 0 is returned
    // instead of an error.
    _, err = sess.SQL().Exec(`SELECT crdb_internal.force_retry('1s'::INTERVAL)`)
    if err != nil {
        return err
    }

    return nil
}

func main() {
    // Connect to the local CockroachDB node.
    sess, err := cockroachdb.Open(settings)
    if err != nil {
        log.Fatal("cockroachdb.Open: ", err)
    }
    defer sess.Close()

    // Adjust this number to fit your specific needs (set to 5, by default)
    // sess.SetMaxTransactionRetries(10)

    // Create the "accounts" table
    createTables(sess)

    // Delete all the previous items in the "accounts" table.
    err = Accounts(sess).Truncate()
    if err != nil {
        log.Fatal("Truncate: ", err)
    }

    // Create a new account with a balance of 1000.
    account1 := Account{Balance: 1000}
    err = Accounts(sess).InsertReturning(&account1)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Create a new account with a balance of 250.
    account2 := Account{Balance: 250}
    err = Accounts(sess).InsertReturning(&account2)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Printing records
    printRecords(sess)

    // Change the balance of the first account.
    account1.Balance = 500
    err = sess.Save(&account1)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Change the balance of the second account.
    account2.Balance = 999
    err = sess.Save(&account2)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Printing records
    printRecords(sess)

    // Delete the first record.
    err = sess.Delete(&account1)
    if err != nil {
        log.Fatal("Delete: ", err)
    }

    startTime := time.Now()

    // Add a couple of new records within a transaction.
    err = sess.Tx(func(tx db.Session) error {
        var err error

        if err = tx.Save(&Account{Balance: 887}); err != nil {
            return err
        }

        if time.Now().Sub(startTime) < time.Second*1 {
            // Will fail continuously for 2 seconds.
            if err = crdbForceRetry(tx); err != nil {
                return err
            }
        }

        if err = tx.Save(&Account{Balance: 342}); err != nil {
            return err
        }

        return nil
    })
    if err != nil {
        log.Fatal("Could not commit transaction: ", err)
    }

    // Printing records
    printRecords(sess)
}

func printRecords(sess db.Session) {
    accounts := []Account{}
    err := Accounts(sess).Find().All(&accounts)
    if err != nil {
        log.Fatal("Find: ", err)
    }
    log.Printf("Balances:")
    for i := range accounts {
        fmt.Printf("\taccounts[%d]: %d\n", accounts[i].ID, accounts[i].Balance)
    }
}

Note that the sample code also includes a function that simulates a transaction error (crdbForceRetry()). Upper/db’s CockroachDB adapter when transaction errors are thrown. As a result, this function forces a transaction retry.

To run the code, copy the sample above, or download it directly.

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

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

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

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 1. Create the maxroach user and bank database

Start the :

$ cockroach sql --insecure

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

> CREATE USER IF NOT EXISTS maxroach;

> CREATE DATABASE bank;

Give the maxroach user the necessary permissions:

> GRANT ALL ON DATABASE bank TO maxroach;

Exit the SQL shell:

> \q

Step 2. Run the Go code

The sample code shown below uses upper/db to map Go-specific objects to SQL operations. Specifically, the code:

• Creates the accounts table, if it does not already exist.
• Deletes any existing rows in the accounts table.
• Inserts two rows into the accounts table.
• Prints the rows in the accounts table to the terminal.
• Deletes the first row in the accounts table.
• Updates the rows in the accounts table within an explicit .
• Prints the rows in the accounts table to the terminal once more.

package main

    "fmt"
    "log"
    "time"

    "github.com/upper/db/v4"
    "github.com/upper/db/v4/adapter/cockroachdb"
)

// The settings variable stores connection details.
var settings = cockroachdb.ConnectionURL{
    Host:     "localhost",
    Database: "bank",
    User:     "maxroach",
    Options: map[string]string{
        // Insecure node.
        "sslmode": "disable",
    },
}

// Accounts is a handy way to represent a collection.
func Accounts(sess db.Session) db.Store {
    return sess.Collection("accounts")
}

// Account is used to represent a single record in the "accounts" table.
type Account struct {
    ID      uint64 `db:"id,omitempty"`
    Balance int64  `db:"balance"`
}

// Collection is required in order to create a relation between the Account
// struct and the "accounts" table.
func (a *Account) Store(sess db.Session) db.Store {
    return Accounts(sess)
}

// createTables creates all the tables that are neccessary to run this example.
func createTables(sess db.Session) error {
    _, err := sess.SQL().Exec(`
        CREATE TABLE IF NOT EXISTS accounts (
            ID SERIAL PRIMARY KEY,
            balance INT
        )
    `)
    if err != nil {
        return err
    }
    return nil
}

// crdbForceRetry can be used to simulate a transaction error and
// demonstrate upper/db's ability to retry the transaction automatically.
//
// By default, upper/db will retry the transaction five times, if you want
// to modify this number use: sess.SetMaxTransactionRetries(n).
//
// This is only used for demonstration purposes and not intended
// for production code.
func crdbForceRetry(sess db.Session) error {
    var err error

    // The first statement in a transaction can be retried transparently on the
    // server, so we need to add a placeholder statement so that our
    // force_retry() statement isn't the first one.
    _, err = sess.SQL().Exec(`SELECT 1`)
    if err != nil {
        return err
    }

    // If force_retry is called during the specified interval from the beginning
    // of the transaction it returns a retryable error. If not, 0 is returned
    // instead of an error.
    _, err = sess.SQL().Exec(`SELECT crdb_internal.force_retry('1s'::INTERVAL)`)
    if err != nil {
        return err
    }

    return nil
}

func main() {
    // Connect to the local CockroachDB node.
    sess, err := cockroachdb.Open(settings)
    if err != nil {
        log.Fatal("cockroachdb.Open: ", err)
    }
    defer sess.Close()

    // Adjust this number to fit your specific needs (set to 5, by default)
    // sess.SetMaxTransactionRetries(10)

    // Create the "accounts" table
    createTables(sess)

    // Delete all the previous items in the "accounts" table.
    err = Accounts(sess).Truncate()
    if err != nil {
        log.Fatal("Truncate: ", err)
    }

    // Create a new account with a balance of 1000.
    account1 := Account{Balance: 1000}
    err = Accounts(sess).InsertReturning(&account1)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Create a new account with a balance of 250.
    account2 := Account{Balance: 250}
    err = Accounts(sess).InsertReturning(&account2)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Printing records
    printRecords(sess)

    // Change the balance of the first account.
    account1.Balance = 500
    err = sess.Save(&account1)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Change the balance of the second account.
    account2.Balance = 999
    err = sess.Save(&account2)
    if err != nil {
        log.Fatal("sess.Save: ", err)
    }

    // Printing records
    printRecords(sess)

    // Delete the first record.
    err = sess.Delete(&account1)
    if err != nil {
        log.Fatal("Delete: ", err)
    }

    startTime := time.Now()

    // Add a couple of new records within a transaction.
    err = sess.Tx(func(tx db.Session) error {
        var err error

        if err = tx.Save(&Account{Balance: 887}); err != nil {
            return err
        }

        if time.Now().Sub(startTime) < time.Second*1 {
            // Will fail continuously for 2 seconds.
            if err = crdbForceRetry(tx); err != nil {
                return err
            }
        }

        if err = tx.Save(&Account{Balance: 342}); err != nil {
            return err
        }

        return nil
    })
    if err != nil {
        log.Fatal("Could not commit transaction: ", err)
    }

    // Printing records
    printRecords(sess)
}

func printRecords(sess db.Session) {
    accounts := []Account{}
    err := Accounts(sess).Find().All(&accounts)
    if err != nil {
        log.Fatal("Find: ", err)
    }
    log.Printf("Balances:")
    for i := range accounts {
        fmt.Printf("\taccounts[%d]: %d\n", accounts[i].ID, accounts[i].Balance)
    }
}

Note that the sample code also includes a function that simulates a transaction error (crdbForceRetry()). Upper/db’s CockroachDB adapter when transaction errors are thrown. As a result, this function forces a transaction retry.

Copy the code or download it directly.

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

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

Change to the directory where you cloned the repo and get the dependencies with go mod init:

$ go mod init hello-world-go-upperdb

Then run the code:

$ go run main.go

The output should look similar to the following:

go: finding module for package github.com/upper/db/v4
go: finding module for package github.com/upper/db/v4/adapter/cockroachdb
go: found github.com/upper/db/v4 in github.com/upper/db/v4 v4.0.0
2020/09/16 10:31:55 Balances:
    accounts[590467288222990337]: 1000
    accounts[590467288229576705]: 250
2020/09/16 10:31:55 Balances:
    accounts[590467288222990337]: 500
    accounts[590467288229576705]: 999
2020/09/16 10:31:55 upper/db: log_level=WARNING file=go/pkg/mod/github.com/upper/db/v4@v4.0.0/internal/sqladapter/session.go:642
    Session ID:     00006
    Transaction ID: 00005
    Query:          SELECT crdb_internal.force_retry('1ms'::INTERVAL)
    Error:          pq: restart transaction: crdb_internal.force_retry(): TransactionRetryWithProtoRefreshError: forced by crdb_internal.force_retry()
    Time taken:     0.00171s
    Context:        context.Background

2020/09/16 10:31:55 upper/db: log_level=WARNING file=go/pkg/mod/github.com/upper/db/v4@v4.0.0/internal/sqladapter/session.go:642
    Session ID:     00006
    Transaction ID: 00005
    Query:          INSERT INTO "accounts" ("balance") VALUES ($1) RETURNING "id"
    Arguments:      []interface {}{887}
    Error:          pq: current transaction is aborted, commands ignored until end of transaction block
    Time taken:     0.00065s
    Context:        context.Background

2020/09/16 10:31:56 Balances:
    accounts[590467288229576705]: 999
    accounts[590467288342757377]: 887
    accounts[590467288350064641]: 342

Note that the forced transaction errors result in errors printed to the terminal, but the transactions are retried until they succeed.

What’s next?

Read more about upper/db:

• Introduction to upper/db
• The upper/db tour
• upper/db reference docs

You might also be interested in the following pages: