added transactions example for database/sql driver

Author: asmyasnikov

examples/transaction/database/sql/README.md

@@ -0,0 +1,8 @@
+# Using transactions over databas/sql driver for YDB
+
+## Runing code snippet
+```bash
+go run -ydb="grpcs://endpoint/?database=database"
+```
+
+

examples/transaction/database/sql/main.go

@@ -0,0 +1,199 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	ydb "github.com/ydb-platform/ydb-go-sdk/v3"
+	"github.com/ydb-platform/ydb-go-sdk/v3/retry"
+)
+
+var dsn string
+
+func init() { //nolint:gochecknoinits
+	required := []string{"ydb"}
+	flagSet := flag.NewFlagSet(os.Args[0], flag.ExitOnError)
+	flagSet.Usage = func() {
+		out := flagSet.Output()
+		_, _ = fmt.Fprintf(out, "Usage:\n%s [options]\n", os.Args[0])
+		_, _ = fmt.Fprintf(out, "\nOptions:\n")
+		flagSet.PrintDefaults()
+	}
+	flagSet.StringVar(&dsn,
+		"ydb", "",
+		"YDB connection string",
+	)
+	if err := flagSet.Parse(os.Args[1:]); err != nil {
+		flagSet.Usage()
+		os.Exit(1)
+	}
+	flagSet.Visit(func(f *flag.Flag) {
+		for i, arg := range required {
+			if arg == f.Name {
+				required = append(required[:i], required[i+1:]...)
+			}
+		}
+	})
+	if len(required) > 0 {
+		fmt.Printf("\nSome required options not defined: %v\n\n", required)
+		flagSet.Usage()
+		os.Exit(1)
+	}
+}
+
+func main() {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	nativeDriver, err := ydb.Open(ctx, dsn)
+	if err != nil {
+		panic(err)
+	}
+	defer nativeDriver.Close(ctx)
+
+	connector, err := ydb.Connector(nativeDriver,
+		ydb.WithAutoDeclare(),
+		ydb.WithQueryService(true),
+	)
+	if err != nil {
+		panic(err)
+	}
+
+	db := sql.OpenDB(connector)
+	defer db.Close()
+
+	if words, err := txWithoutRetries(ctx, db); err != nil {
+		panic(err)
+	} else {
+		fmt.Printf("SUCCESS: %q\n", strings.Join(words, " "))
+	}
+
+	if words, err := txWithRetries(ctx, db); err != nil {
+		panic(err)
+	} else {
+		fmt.Printf("SUCCESS: %q\n", strings.Join(words, " "))
+	}
+}
+
+func txWithoutRetries(ctx context.Context, db *sql.DB) (words []string, _ error) {
+	tx, err := db.BeginTx(ctx, &sql.TxOptions{
+		Isolation: sql.LevelDefault,
+		ReadOnly:  false,
+	})
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	row := tx.QueryRowContext(ctx, "SELECT 'execute';")
+
+	var word string
+	err = row.Scan(&word)
+	if err != nil {
+		return nil, err
+	}
+
+	words = append(words, word)
+
+	rows, err := tx.QueryContext(ctx, `
+			SELECT w, ord FROM (
+				SELECT $word1 AS w, 1 AS ord 
+				UNION 
+				SELECT $word2 AS w, 2 AS ord
+				UNION 
+				SELECT 'without'u AS w, 3 AS ord
+				UNION 
+				SELECT $word3 AS w, 4 AS ord
+			)
+			ORDER BY ord;
+		`,
+		sql.Named("word1", "in"),
+		sql.Named("word2", "transaction"),
+		sql.Named("word3", "retries"),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	for rows.Next() {
+		var (
+			word string
+			ord  int
+		)
+		if err = rows.Scan(&word, &ord); err != nil {
+			return nil, err
+		}
+		words = append(words, word)
+	}
+
+	if err = rows.Err(); err != nil {
+		return nil, err
+	}
+
+	if err = tx.Commit(); err != nil {
+		return nil, err
+	}
+
+	return words, nil
+}
+
+func txWithRetries(ctx context.Context, db *sql.DB) (words []string, _ error) {
+	err := retry.DoTx(ctx, db, func(ctx context.Context, tx *sql.Tx) error {
+		words = words[:0] // empty for new retry attempt
+
+		row := tx.QueryRowContext(ctx, "SELECT 'execute';")
+
+		var word string
+		err := row.Scan(&word)
+		if err != nil {
+			return err
+		}
+
+		words = append(words, word)
+
+		rows, err := tx.QueryContext(ctx, `
+				SELECT w, ord FROM (
+					SELECT $word1 AS w, 1 AS ord 
+					UNION 
+					SELECT $word2 AS w, 2 AS ord
+					UNION 
+					SELECT 'with'u AS w, 3 AS ord
+					UNION 
+					SELECT $word3 AS w, 4 AS ord
+					UNION 
+					SELECT 'using'u AS w, 5 AS ord
+					UNION 
+					SELECT 'retry.DoTx'u AS w, 6 AS ord
+				)
+				ORDER BY ord;
+			`,
+			sql.Named("word1", "in"),
+			sql.Named("word2", "transaction"),
+			sql.Named("word3", "retries"),
+		)
+		if err != nil {
+			return err
+		}
+
+		for rows.Next() {
+			var (
+				word string
+				ord  int
+			)
+			if err = rows.Scan(&word, &ord); err != nil {
+				return err
+			}
+			words = append(words, word)
+		}
+
+		return rows.Err()
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return words, nil
+}