This tutorial shows you how build a simple Go application with CockroachDB using a PostgreSQL-compatible driver or ORM. We've tested and can recommend the Go pq driver and the GORM ORM, so those are featured here.
Before You Begin
Make sure you have already installed CockroachDB.
Step 1. Install the Go pq driver
To install the Go pq driver, run the following command:
$ go get -u github.com/lib/pq
Step 2. Start a single-node cluster
For the purpose of this tutorial, you need only one CockroachDB node running in insecure mode:
$ cockroach start \
--insecure \
--store=hello-1 \
--host=localhost
Step 3. Create a user
In a new terminal, as the root user, use the cockroach user command to create a new user, maxroach.
$ cockroach user set maxroach --insecure
Step 4. Create a database and grant privileges
As the root user, use the built-in SQL client to create a bank database.
$ cockroach sql --insecure -e 'CREATE DATABASE bank'
Then grant privileges to the maxroach user.
$ cockroach sql --insecure -e 'GRANT ALL ON DATABASE bank TO maxroach'
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.
Basic Statements
First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.
Download the basic-sample.go file, or create the file yourself and copy the code into it.
package main
import (
"database/sql"
"fmt"
"log"
_ "github.com/lib/pq"
)
func main() {
// Connect to the "bank" database.
db, err := sql.Open("postgres", "postgresql://maxroach@localhost:26257/bank?sslmode=disable")
if err != nil {
log.Fatal("error connecting to the database: ", err)
}
// 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.
rows, err := db.Query("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)
}
}
Then run the code:
$ go run basic-sample.go
The output should be:
Initial balances:
1 1000
2 250
Transaction (with retry logic)
Next, use the following code to again connect as the maxroach user but this time will execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.
Download the txn-sample.go file, or create the file yourself and copy the code into it.
package main
import (
"context"
"database/sql"
"fmt"
"log"
"github.com/cockroachdb/cockroach-go/crdb"
)
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", "postgresql://maxroach@localhost:26257/bank?sslmode=disable")
if err != nil {
log.Fatal("error connecting to the database: ", err)
}
// 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)
}
}
With the default SERIALIZABLE isolation level, CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. For Go, the CockroachDB retry function is in the crdb package of the CockroachDB Go client. Clone the library into your $GOPATH as follows:
$ mkdir -p $GOPATH/src/github.com/cockroachdb
$ cd $GOPATH/src/github.com/cockroachdb
$ git clone git@github.com:cockroachdb/cockroach-go.git
Then run the code:
$ go run txn-sample.go
The output should just be:
Success
However, if you want to verify that funds were transferred from one account to another, use the built-in SQL client:
$ 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 pq driver.
You might also be interested in using a local cluster to explore the following core CockroachDB features:
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