Merge pull request cockroachdb#8261 from cockroachdb/gorm-sample-updates

Updates to GORM hello world sample and tutorial

_includes/v20.2/app/gorm-basic-sample/main.go

@@ -0,0 +1,122 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"time"
+
+	// Import GORM-related packages.
+	"github.com/cockroachdb/cockroach-go/crdb/crdbgorm"
+	"github.com/jinzhu/gorm"
+	_ "github.com/jinzhu/gorm/dialects/postgres"
+)
+
+// Account is our model, which corresponds to the "accounts" database
+// table.
+type Account struct {
+	ID      int `gorm:"primary_key"`
+	Balance int
+}
+
+// Functions of type `txnFunc` are passed as arguments to the
+// `ExecuteTx` wrapper that handles transaction retries
+type txnFunc func(*gorm.DB) error
+
+func transferFunds(db *gorm.DB, fromID int, toID int, amount int) error {
+	var fromAccount Account
+	var toAccount Account
+
+	db.First(&fromAccount, fromID)
+	db.First(&toAccount, toID)
+
+	if fromAccount.Balance < amount {
+		return fmt.Errorf("account %d 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
+	}
+	return nil
+}
+
+func main() {
+	// Connect to the "bank" database as the "maxroach" user.
+	const addr = "postgresql://maxroach@localhost:26257/bank?ssl=true&sslmode=require&sslrootcert=certs/ca.crt&sslkey=certs/client.maxroach.key&sslcert=certs/client.maxroach.crt"
+	db, err := gorm.Open("postgres", addr)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer db.Close()
+
+	// Set to `true` and GORM will print out all DB queries.
+	db.LogMode(false)
+
+	// Automatically create the "accounts" table based on the Account
+	// model.
+	db.AutoMigrate(&Account{})
+
+	// Insert two rows into the "accounts" table.
+	var fromID = 1
+	var toID = 2
+	db.Create(&Account{ID: fromID, Balance: 1000})
+	db.Create(&Account{ID: toID, Balance: 250})
+
+	// The sequence of steps in this section is:
+	// 1. Print account balances.
+	// 2. Set up some Accounts and transfer funds between them inside
+	// a transaction.
+	// 3. Print account balances again to verify the transfer occurred.
+
+	// Print balances before transfer.
+	printBalances(db)
+
+	// The amount to be transferred between the accounts.
+	var amount = 100
+
+	// Transfer funds between accounts.  To handle potential
+	// transaction retry errors, we wrap the call to `transferFunds`
+	// in `crdbgorm.ExecuteTx`, a helper function for GORM which
+	// implements a retry loop
+	if err := crdbgorm.ExecuteTx(context.Background(), db, nil,
+		func(*gorm.DB) error {
+			return transferFunds(db, fromID, toID, amount)
+		},
+	); 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 accounts so we can start fresh when we want to run this
+	// program again.
+	deleteAccounts(db)
+}
+
+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("%d %d\n", account.ID, account.Balance)
+	}
+}
+
+func deleteAccounts(db *gorm.DB) error {
+	// Used to tear down the accounts table so we can re-run this
+	// program.
+	err := db.Exec("DELETE from accounts where ID > 0").Error
+	if err != nil {
+		return err
+	}
+	return nil
+}