This tutorial shows you how build a simple CRUD Go application with CockroachDB and the GORM ORM.
For another use of GORM with CockroachDB, see our examples-orms
repository.
Step 1. Start CockroachDB
Create a free 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 Create your cluster page, select Serverless.
Click Create cluster.
Your cluster will be created in a few seconds and the Create SQL user dialog will display.
Create a SQL user
The Create SQL user dialog allows you to create a new SQL user and password.
- Enter a username in the SQL user field or use the one provided by default.
- Click Generate & save password.
- Copy the generated password and save it in a secure location.
Click Next.
Currently, all new users are created with full privileges. For more information and to change the default settings, see [Manage SQL users on a cluster.
Get the connection string
The Connect to cluster dialog shows information about how to connect to your cluster.
- Select General connection string from the Select option dropdown.
Open the General connection string section, then copy the connection string provided and save it in a secure location.
The sample application used in this tutorial uses system CA certificates for server certificate verification, so you can skip the Download CA Cert instructions.
Note:The connection string is pre-populated with your username, password, cluster name, and other details. Your password, in particular, will be provided only once. Save it in a secure place (Cockroach Labs recommends a password manager) to connect to your cluster in the future. 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
.
- If you haven't already, download the CockroachDB binary.
Run the
cockroach start-single-node
command:$ cockroach start-single-node --advertise-addr 'localhost' --insecure
This starts an insecure, single-node cluster.
Take note of the following connection information in the SQL shell welcome text:
CockroachDB node starting at 2021-08-30 17:25:30.06524 +0000 UTC (took 4.3s) build: CCL v21.1.6 @ 2021/07/20 15:33:43 (go1.15.11) webui: http://localhost:8080 sql: postgresql://root@localhost:26257?sslmode=disable
You'll use the
sql
connection string to connect to the cluster later in this tutorial.
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 2. Get the code
Clone the code's GitHub repo:
$ git clone https://github.com/cockroachlabs/example-app-go-gorm
The project has the following directory structure:
├── README.md
└── main.go
The main.go
file defines an Account
struct that maps to a new accounts
table. The file also contains some read and write database operations that are executed in the main
method of the program.
package main
import (
"context"
"fmt"
"log"
"math/rand"
"os"
"time"
"github.com/cockroachdb/cockroach-go/v2/crdb/crdbgorm"
"github.com/google/uuid"
"gorm.io/driver/postgres"
"gorm.io/gorm"
)
// Account is our model, which corresponds to the "accounts" table
type Account struct {
ID uuid.UUID `gorm:"type:uuid;default:uuid_generate_v4()"`
Balance int
}
// The `acctIDs` global variable tracks the random IDs generated by `addAccounts`
var acctIDs []uuid.UUID
// Insert new rows into the "accounts" table
// This function generates new UUIDs and random balances for each row, and
// then it appends the ID to the `acctIDs`, which other functions use to track the IDs
func addAccounts(db *gorm.DB, numRows int, transferAmount int) error {
log.Printf("Creating %d new accounts...", numRows)
for i := 0; i < numRows; i++ {
newID := uuid.New()
newBalance := rand.Intn(10000) + transferAmount
if err := db.Create(&Account{ID: newID, Balance: newBalance}).Error; err != nil {
return err
}
acctIDs = append(acctIDs, newID)
}
log.Println("Accounts created.")
return nil
}
// Transfer funds between accounts
// This function adds `amount` to the "balance" column of the row with the "id" column matching `toID`,
// and removes `amount` from the "balance" column of the row with the "id" column matching `fromID`
func transferFunds(db *gorm.DB, fromID uuid.UUID, toID uuid.UUID, amount int) error {
log.Printf("Transferring %d from account %s to account %s...", amount, fromID, toID)
var fromAccount Account
var toAccount Account
db.First(&fromAccount, fromID)
db.First(&toAccount, toID)
if fromAccount.Balance < amount {
return fmt.Errorf("account %s balance %d is lower than transfer amount %d", fromAccount.ID, fromAccount.Balance, amount)
}
fromAccount.Balance -= amount
toAccount.Balance += amount
if err := db.Save(&fromAccount).Error; err != nil {
return err
}
if err := db.Save(&toAccount).Error; err != nil {
return err
}
log.Println("Funds transferred.")
return nil
}
// Print IDs and balances for all rows in "accounts" table
func printBalances(db *gorm.DB) {
var accounts []Account
db.Find(&accounts)
fmt.Printf("Balance at '%s':\n", time.Now())
for _, account := range accounts {
fmt.Printf("%s %d\n", account.ID, account.Balance)
}
}
// Delete all rows in "accounts" table inserted by `main` (i.e., tracked by `acctIDs`)
func deleteAccounts(db *gorm.DB, accountIDs []uuid.UUID) error {
log.Println("Deleting accounts created...")
err := db.Where("id IN ?", accountIDs).Delete(Account{}).Error
if err != nil {
return err
}
log.Println("Accounts deleted.")
return nil
}
func main() {
db, err := gorm.Open(postgres.Open(os.Getenv("DATABASE_URL")+"&application_name=$ docs_simplecrud_gorm"), &gorm.Config{})
if err != nil {
log.Fatal(err)
}
// Automatically create the "accounts" table based on the `Account`
// model.
db.AutoMigrate(&Account{})
// The number of initial rows to insert
const numAccts int = 5
// The amount to be transferred between two accounts.
const transferAmt int = 100
// Insert `numAccts` rows into the "accounts" table.
// To handle potential transaction retry errors, we wrap the call
// to `addAccounts` in `crdbgorm.ExecuteTx`, a helper function for
// GORM which implements a retry loop
if err := crdbgorm.ExecuteTx(context.Background(), db, nil,
func(tx *gorm.DB) error {
return addAccounts(db, numAccts, transferAmt)
},
); err != nil {
// For information and reference documentation, see:
// https://www.cockroachlabs.com/docs/stable/error-handling-and-troubleshooting.html
fmt.Println(err)
}
// Print balances before transfer.
printBalances(db)
// Select two account IDs
fromID := acctIDs[0]
toID := acctIDs[0:][rand.Intn(len(acctIDs))]
// Transfer funds between accounts. To handle potential
// transaction retry errors, we wrap the call to `transferFunds`
// in `crdbgorm.ExecuteTx`
if err := crdbgorm.ExecuteTx(context.Background(), db, nil,
func(tx *gorm.DB) error {
return transferFunds(tx, fromID, toID, transferAmt)
},
); err != nil {
// For information and reference documentation, see:
// https://www.cockroachlabs.com/docs/stable/error-handling-and-troubleshooting.html
fmt.Println(err)
}
// Print balances after transfer to ensure that it worked.
printBalances(db)
// Delete all accounts created by the earlier call to `addAccounts`
// To handle potential transaction retry errors, we wrap the call
// to `deleteAccounts` in `crdbgorm.ExecuteTx`
if err := crdbgorm.ExecuteTx(context.Background(), db, nil,
func(tx *gorm.DB) error {
return deleteAccounts(db, acctIDs)
},
); err != nil {
// For information and reference documentation, see:
// https://www.cockroachlabs.com/docs/stable/error-handling-and-troubleshooting.html
fmt.Println(err)
}
}
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.
Step 3. Run the code
Initialize the module:
$ cd example-app-go-gorm
$ go mod init basic-sample && go mod tidy
Run the code:
$ go run main.go
The output should look similar to the following:
2021/09/16 14:17:12 Creating 5 new accounts... 2021/09/16 14:17:12 Accounts created. Balance at '2021-09-16 14:17:12.68843 -0400 EDT m=+2.760587790': 1580d2f4-c9ec-4f26-bbe7-6a53e9aa5170 1947 26ddc77b-8068-409b-b305-0c5d873f7c43 7987 3d97ea5a-5108-4388-88e8-92524d5de5e8 4159 af49831d-d637-4a20-a9a7-01e9fe4628fe 8181 f0cc97ef-e3fe-4abb-a44a-0dd04207f7d4 2181 2021/09/16 14:17:12 Transferring 100 from account af49831d-d637-4a20-a9a7-01e9fe4628fe to account 3d97ea5a-5108-4388-88e8-92524d5de5e8... 2021/09/16 14:17:12 Funds transferred. Balance at '2021-09-16 14:17:12.759686 -0400 EDT m=+2.831841311': 1580d2f4-c9ec-4f26-bbe7-6a53e9aa5170 1947 26ddc77b-8068-409b-b305-0c5d873f7c43 7987 3d97ea5a-5108-4388-88e8-92524d5de5e8 4259 af49831d-d637-4a20-a9a7-01e9fe4628fe 8081 f0cc97ef-e3fe-4abb-a44a-0dd04207f7d4 2181 2021/09/16 14:17:12 Deleting accounts created... 2021/09/16 14:17:12 Accounts deleted.
The code runs a migration that creates the
accounts
table in thebank
database, based on theAccount
struct defined at the top of themain.go
file.As shown in the output, the code also does the following:
- Inserts some rows into the
accounts
table. - Reads values from the table.
- Updates values in the table.
- Deletes values from the table.
- Inserts some rows into the
What's next?
Read more about using the GORM ORM, or check out a more realistic implementation of GORM with CockroachDB in our examples-orms
repository.
You might also be interested in the following pages: