added transactions example for table client

Author: asmyasnikov

examples/transaction/table/README.md

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

examples/transaction/table/main.go

@@ -0,0 +1,149 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	ydb "github.com/ydb-platform/ydb-go-sdk/v3"
+	"github.com/ydb-platform/ydb-go-sdk/v3/table"
+	"github.com/ydb-platform/ydb-go-sdk/v3/table/types"
+)
+
+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()
+	db, err := ydb.Open(ctx, dsn)
+	if err != nil {
+		panic(err)
+	}
+	defer db.Close(ctx)
+
+	if words, err := txWithRetries(ctx, db); err != nil {
+		panic(err)
+	} else {
+		fmt.Printf("SUCCESS: %q\n", strings.Join(words, " "))
+	}
+}
+
+func txWithRetries(ctx context.Context, db *ydb.Driver) (words []string, _ error) {
+	err := db.Table().DoTx(ctx, func(ctx context.Context, tx table.TransactionActor) error {
+		words = words[:0] // empty for new retry attempt
+
+		result, err := tx.Execute(ctx, "SELECT 'execute';", nil)
+		if err != nil {
+			return err
+		}
+
+		if err := result.NextResultSetErr(ctx); err != nil {
+			return err
+		}
+
+		if !result.NextRow() {
+			return fmt.Errorf("no row")
+		}
+
+		var s string
+		if err := result.Scan(&s); err != nil {
+			return err
+		}
+
+		words = append(words, s)
+
+		if err = result.Err(); err != nil {
+			return err
+		}
+
+		_ = result.Close()
+
+		result, err = tx.Execute(ctx, `
+				DECLARE $word1 AS Text;
+				DECLARE $word2 AS Text;
+				DECLARE $word3 AS Text;
+
+				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 $word3 AS w, 4 AS ord
+					UNION 
+					SELECT 'using'u AS w, 5 AS ord
+					UNION 
+					SELECT 'db.Table().DoTx()'u AS w, 6 AS ord
+				)
+				ORDER BY ord;
+			`,
+			table.NewQueryParameters(
+				table.ValueParam("$word1", types.TextValue("in")),
+				table.ValueParam("$word2", types.TextValue("transaction")),
+				table.ValueParam("$word3", types.TextValue("retries")),
+			),
+		)
+		if err != nil {
+			return err
+		}
+
+		defer result.Close()
+
+		if err := result.NextResultSetErr(ctx); err != nil {
+			return err
+		}
+
+		for result.NextRow() {
+			var (
+				word string
+				ord  int
+			)
+			err = result.Scan(&word, &ord)
+			if err != nil {
+				return err
+			}
+			words = append(words, word)
+		}
+
+		return result.Err()
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return words, nil
+}