snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

_examples/real-world-examples/synchronizing-databases/main.go

@@ -0,0 +1,195 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	stdSQL "database/sql"
+	"encoding/gob"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/brianvoe/gofakeit/v6"
+	driver "github.com/go-sql-driver/mysql"
+	_ "github.com/lib/pq"
+
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/ThreeDotsLabs/watermill-sql/v4/pkg/sql"
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/ThreeDotsLabs/watermill/message/router/middleware"
+	"github.com/ThreeDotsLabs/watermill/message/router/plugin"
+)
+
+var (
+	logger        = watermill.NewStdLogger(false, false)
+	postgresTable = "users"
+	mysqlTable    = "users"
+)
+
+func main() {
+	router, err := message.NewRouter(message.RouterConfig{}, logger)
+	if err != nil {
+		panic(err)
+	}
+
+	router.AddPlugin(plugin.SignalsHandler)
+	router.AddMiddleware(middleware.Recoverer)
+
+	mysqlDB := createMySQLConnection()
+	postgresDB := createPostgresConnection()
+
+	subscriber := createSubscriber(mysqlDB)
+	publisher := createPublisher(postgresDB)
+
+	go simulateEvents(mysqlDB)
+
+	router.AddHandler(
+		"mysql-to-postgres",
+		mysqlTable,
+		subscriber,
+		postgresTable,
+		publisher,
+		func(msg *message.Message) ([]*message.Message, error) {
+			originUser := mysqlUser{}
+
+			decoder := gob.NewDecoder(bytes.NewBuffer(msg.Payload))
+			err := decoder.Decode(&originUser)
+			if err != nil {
+				return nil, err
+			}
+
+			log.Printf("received user: %+v", originUser)
+
+			newUser := postgresUser{
+				ID:        originUser.ID,
+				Username:  originUser.User,
+				FullName:  fmt.Sprintf("%s %s", originUser.FirstName, originUser.LastName),
+				CreatedAt: originUser.CreatedAt,
+			}
+
+			var payload bytes.Buffer
+			encoder := gob.NewEncoder(&payload)
+			err = encoder.Encode(newUser)
+			if err != nil {
+				return nil, err
+			}
+
+			newMessage := message.NewMessage(watermill.NewULID(), payload.Bytes())
+
+			return []*message.Message{newMessage}, nil
+		},
+	)
+
+	if err := router.Run(context.Background()); err != nil {
+		panic(err)
+	}
+}
+
+func createMySQLConnection() *stdSQL.DB {
+	conf := driver.NewConfig()
+	conf.Net = "tcp"
+	conf.User = "root"
+	conf.Addr = "mysql"
+	conf.DBName = "watermill"
+	conf.ParseTime = true
+
+	db, err := stdSQL.Open("mysql", conf.FormatDSN())
+	if err != nil {
+		panic(err)
+	}
+
+	err = db.Ping()
+	if err != nil {
+		panic(err)
+	}
+
+	return db
+}
+
+func createPostgresConnection() *stdSQL.DB {
+	dsn := "postgres://watermill:password@postgres/watermill?sslmode=disable"
+	db, err := stdSQL.Open("postgres", dsn)
+	if err != nil {
+		panic(err)
+	}
+
+	err = db.Ping()
+	if err != nil {
+		panic(err)
+	}
+
+	return db
+}
+
+func createSubscriber(db *stdSQL.DB) message.Subscriber {
+	sub, err := sql.NewSubscriber(
+		sql.BeginnerFromStdSQL(db),
+		sql.SubscriberConfig{
+			SchemaAdapter:    mysqlSchemaAdapter{},
+			OffsetsAdapter:   sql.DefaultMySQLOffsetsAdapter{},
+			InitializeSchema: true,
+		},
+		logger,
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	return sub
+}
+
+func createPublisher(db *stdSQL.DB) message.Publisher {
+	pub, err := sql.NewPublisher(
+		sql.BeginnerFromStdSQL(db),
+		sql.PublisherConfig{
+			SchemaAdapter:        postgresSchemaAdapter{},
+			AutoInitializeSchema: true,
+		},
+		logger,
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	return pub
+}
+
+func simulateEvents(db *stdSQL.DB) {
+	pub, err := sql.NewPublisher(
+		sql.BeginnerFromStdSQL(db),
+		sql.PublisherConfig{
+			SchemaAdapter:        mysqlSchemaAdapter{},
+			AutoInitializeSchema: true,
+		},
+		logger,
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	for {
+		user := mysqlUser{
+			User:      gofakeit.Username(),
+			FirstName: gofakeit.FirstName(),
+			LastName:  gofakeit.LastName(),
+			CreatedAt: time.Now().UTC(),
+		}
+
+		var payload bytes.Buffer
+		encoder := gob.NewEncoder(&payload)
+		err := encoder.Encode(user)
+		if err != nil {
+			panic(err)
+		}
+
+		err = pub.Publish(mysqlTable, message.NewMessage(
+			watermill.NewUUID(),
+			payload.Bytes(),
+		))
+		if err != nil {
+			panic(err)
+		}
+
+		time.Sleep(time.Second)
+	}
+}