Blog Code: Clean SQL Transactions in Golang

main_1.go

package main

import (
	"database/sql"
	"log"
)

func main() {
	db, err := sql.Open("VENDOR_HERE", "YOUR_DSN_HERE")
	handleError(err)

	defer db.Close()

	tx, err := db.Begin()
	handleError(err)

	// insert a record into table1
	res, err := tx.Exec("INSERT INTO table1(name) VALUES(?)", "some name")
	if err != nil {
		tx.Rollback()
		log.Fatal(err)
	}

	// fetch the auto incremented id
	id, err := res.LastInsertId()
	handleError(err)

	// insert record into table2, referencing the first record from table1
	res, err = tx.Exec("INSERT INTO table2(table1_id, name) VALUES(?, ?)", id, "other name")
	if err != nil {
		tx.Rollback()
		log.Fatal(err)
	}

	// commit the transaction
	handleError(tx.Commit())

	log.Println("Done.")
}

func handleError(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

main_2.go

package main

import (
	"database/sql"
	"log"
)

func main() {
	db, err := sql.Open("VENDOR_HERE", "YOUR_DSN_HERE")
	handleError(err)

	defer db.Close()

	err = WithTransaction(db, func(tx Transaction) error {
		// insert a record into table1
		res, err := tx.Exec("INSERT INTO table1(name) VALUES(?)", "some name")
		if err != nil {
			return err
		}

		id, err := res.LastInsertId()
		if err != nil {
			return err
		}

		res, err = tx.Exec("INSERT INTO table2(table1_id, name) VALUES(?, ?)", id, "other name")
		if err != nil {
			return err
		}
	})

	handleError(err)
	log.Println("Done.")
}

func handleError(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

main_3.go

package main

import (
	"database/sql"
	"log"
)

func main() {
	db, err := sql.Open("VENDOR_HERE", "YOUR_DSN_HERE")
	handleError(err)

	defer db.Close()

	stmts := []*PipelineStmt{
		NewPipelineStmt("INSERT INTO table1(name) VALUES(?)", "some name"),
		NewPipelineStmt("INSERT INTO table2(table1_id, name) VALUES({LAST_INS_ID}, ?)", "other name"),
	}

	err = WithTransaction(db, func(tx Transaction) error {
		_, err := RunPipeline(tx, stmts...)
		return err
	})

	handleError(err)
	log.Println("Done.")
}

func handleError(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

pipeline.go

package main

import (
	"database/sql"
	"strconv"
	"strings"
)

// A PipelineStmt is a simple wrapper for creating a statement consisting of
// a query and a set of arguments to be passed to that query.
type PipelineStmt struct {
	query string
	args  []interface{}
}

func NewPipelineStmt(query string, args ...interface{}) *PipelineStmt {
	return &PipelineStmt{query, args}
}

// Executes the statement within supplied transaction. The literal string `{LAST_INS_ID}` 
// will be replaced with the supplied value to make chaining `PipelineStmt` objects together 
// simple.
func (ps *PipelineStmt) Exec(tx Transaction, lastInsertId int64) (sql.Result, error) {
	query := strings.Replace(ps.query, "{LAST_INS_ID}", strconv.Itoa(int(lastInsertId)), -1)
	return tx.Exec(query, ps.args...)
}

// Runs the supplied statements within the transaction. If any statement fails, the transaction
// is rolled back, and the original error is returned.
//
// The `LastInsertId` from the previous statement will be passed to `Exec`. The zero-value (0) is
// used initially.
func RunPipeline(tx Transaction, stmts ...*PipelineStmt) (sql.Result, error) {
	var res sql.Result
	var err error
	var lastInsId int64

	for _, ps := range stmts {
		res, err = ps.Exec(tx, lastInsId)
		if err != nil {
			return nil, err
		}

		lastInsId, err = res.LastInsertId()
		if err != nil {
			return nil, err
		}
	}

	return res, nil
}

transaction.go

package main

import (
	"database/sql"
)

// Transaction is an interface that models the standard transaction in
// `database/sql`.
//
// To ensure `TxFn` funcs cannot commit or rollback a transaction (which is
// handled by `WithTransaction`), those methods are not included here.
type Transaction interface {
	Exec(query string, args ...interface{}) (sql.Result, error)
	Prepare(query string) (*sql.Stmt, error)
	Query(query string, args ...interface{}) (*sql.Rows, error)
	QueryRow(query string, args ...interface{}) *sql.Row
}

// A Txfn is a function that will be called with an initialized `Transaction` object
// that can be used for executing statements and queries against a database.
type TxFn func(Transaction) error

// WithTransaction creates a new transaction and handles rollback/commit based on the 
// error object returned by the `TxFn`
func WithTransaction(db *sql.DB, fn TxFn) (err error) {
	tx, err := db.Begin()
	if err != nil {
		return
	}

	defer func() {
		if p := recover(); p != nil {
			// a panic occurred, rollback and repanic
			tx.Rollback()
			panic(p)
		} else if err != nil {
			// something went wrong, rollback
			tx.Rollback()
		} else {
			// all good, commit
			err = tx.Commit()
		}
	}()

	err = fn(tx)
	return err
}

I want to be able to create transactions at the service/use case layer. The problem I'm facing is db *sql.DB required by func WithTransaction(db *sql.DB, fn TxFn) is not available in the service layer. Is there a way to get the transaction at the service layer?

@pranayhere https://medium.com/@enverbisevac/simple-db-transaction-handling-in-go-91a0ff57a4ac

I want to be able to create transactions at the service/use case layer. The problem I'm facing is db *sql.DB required by func WithTransaction(db *sql.DB, fn TxFn) is not available in the service layer. Is there a way to get the transaction at the service layer?

package tx

import (
	"context"
	"database/sql"
	"noname/constant"

	"github.com/rs/zerolog/log"
)

type Queries interface {
	Exec(query string, args ...interface{}) (sql.Result, error)
	Prepare(query string) (*sql.Stmt, error)
	Query(query string, args ...interface{}) (*sql.Rows, error)
	QueryRow(query string, args ...interface{}) *sql.Row
	ExecContext(ctx context.Context, query string, args ...interface{}) (sql.Result, error)
	PrepareContext(ctx context.Context, query string) (*sql.Stmt, error)
	QueryContext(ctx context.Context, query string, args ...interface{}) (*sql.Rows, error)
	QueryRowContext(ctx context.Context, query string, args ...interface{}) *sql.Row
}

type DB interface {
	Begin() (*sql.Tx, error)
	BeginTx(ctx context.Context, opts *sql.TxOptions) (*sql.Tx, error)
}

type Tr struct {
	db DB
}

func NewTransaction(db DB) *Tr {
	return &Tr{
		db: db,
	}
}

type TxFn func(context.Context) error

func (tr *Tr) WithTransaction(ctx context.Context, fn TxFn) (err error) {
	tx, err := tr.db.BeginTx(ctx, nil)
	if err != nil {
		return
	}

	defer func() {
		if err != nil {
			log.Info().Msg("Rollback")
			tx.Rollback()
		} else {
			tx.Commit()
		}
	}()

	ctx = context.WithValue(ctx, constant.KeyTx, tx)
	err = fn(ctx)

	return
}