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

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

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"bytes"
+	"encoding/gob"
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/ThreeDotsLabs/watermill-sql/v4/pkg/sql"
+)
+
+type postgresUser struct {
+	ID        int64
+	Username  string
+	FullName  string
+	CreatedAt time.Time
+}
+
+type postgresSchemaAdapter struct {
+	sql.DefaultPostgreSQLSchema
+}
+
+func (p postgresSchemaAdapter) SchemaInitializingQueries(params sql.SchemaInitializingQueriesParams) ([]sql.Query, error) {
+	createQuery := `
+		CREATE TABLE IF NOT EXISTS ` + params.Topic + ` (
+			id INT NOT NULL PRIMARY KEY,
+			username VARCHAR(36) NOT NULL,
+			full_name VARCHAR(36) NOT NULL,
+			created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+		);
+	`
+
+	return []sql.Query{{Query: createQuery}}, nil
+}
+
+func (p postgresSchemaAdapter) InsertQuery(params sql.InsertQueryParams) (sql.Query, error) {
+	insertQuery := fmt.Sprintf(
+		`INSERT INTO %s (id, username, full_name, created_at) VALUES %s`,
+		params.Topic,
+		strings.TrimRight(strings.Repeat(`($1,$2,$3,$4),`, len(params.Msgs)), ","),
+	)
+
+	var args []interface{}
+	for _, msg := range params.Msgs {
+		user := postgresUser{}
+
+		decoder := gob.NewDecoder(bytes.NewBuffer(msg.Payload))
+		err := decoder.Decode(&user)
+		if err != nil {
+			return sql.Query{}, err
+		}
+
+		args = append(args, user.ID, user.Username, user.FullName, user.CreatedAt)
+	}
+
+	return sql.Query{Query: insertQuery, Args: args}, nil
+}
+
+func (p postgresSchemaAdapter) SelectQuery(params sql.SelectQueryParams) (sql.Query, error) {
+	// No need to implement this method, as PostgreSQL subscriber is not used in this example.
+	return sql.Query{}, nil
+}
+
+func (p postgresSchemaAdapter) UnmarshalMessage(params sql.UnmarshalMessageParams) (sql.Row, error) {
+	return sql.Row{}, errors.New("not implemented")
+}