Transaction isolation levels (go-sql-driver#619)

* Added Gogland IDE internal directory to .gitignore

* Support transaction isolation level in BeginTx

* Review fixes

* Simplyfied TestContextBeginIsolationLevel test

* Applied more review comments

* Applied review remarks

Author: zimnx

.gitignore

@@ -6,3 +6,4 @@
 Icon?
 ehthumbs.db
 Thumbs.db
+.idea

AUTHORS

@@ -46,6 +46,7 @@ Lion Yang <lion at aosc.xyz>
 Luca Looz <luca.looz92 at gmail.com>
 Lucas Liu <extrafliu at gmail.com>
 Luke Scott <luke at webconnex.com>
+Maciej Zimnoch <maciej.zimnoch@codilime.com>
 Michael Woolnough <michael.woolnough at gmail.com>
 Nicola Peduzzi <thenikso at gmail.com>
 Olivier Mengué <dolmen at cpan.org>

connection_go18.go

@@ -41,10 +41,6 @@ func (mc *mysqlConn) Ping(ctx context.Context) error {
 
 // BeginTx implements driver.ConnBeginTx interface
 func (mc *mysqlConn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx, error) {
-	if sql.IsolationLevel(opts.Isolation) != sql.LevelDefault {
-		// TODO: support isolation levels
-		return nil, errors.New("mysql: isolation levels not supported")
-	}
 	if opts.ReadOnly {
 		// TODO: support read-only transactions
 		return nil, errors.New("mysql: read-only transactions not supported")
@@ -54,19 +50,20 @@ func (mc *mysqlConn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver
 		return nil, err
 	}
 
-	tx, err := mc.Begin()
-	mc.finish()
-	if err != nil {
-		return nil, err
-	}
+	defer mc.finish()
 
-	select {
-	default:
-	case <-ctx.Done():
-		tx.Rollback()
-		return nil, ctx.Err()
+	if sql.IsolationLevel(opts.Isolation) != sql.LevelDefault {
+		level, err := mapIsolationLevel(opts.Isolation)
+		if err != nil {
+			return nil, err
+		}
+		err = mc.exec("SET TRANSACTION ISOLATION LEVEL " + level)
+		if err != nil {
+			return nil, err
+		}
 	}
-	return tx, err
+
+	return mc.Begin()
 }
 
 func (mc *mysqlConn) QueryContext(ctx context.Context, query string, args []driver.NamedValue) (driver.Rows, error) {

driver_go18_test.go

@@ -468,3 +468,55 @@ func TestContextCancelBegin(t *testing.T) {
 		}
 	})
 }
+
+func TestContextBeginIsolationLevel(t *testing.T) {
+	runTests(t, dsn, func(dbt *DBTest) {
+		dbt.mustExec("CREATE TABLE test (v INTEGER)")
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		tx1, err := dbt.db.BeginTx(ctx, &sql.TxOptions{
+			Isolation: sql.LevelRepeatableRead,
+		})
+		if err != nil {
+			dbt.Fatal(err)
+		}
+
+		tx2, err := dbt.db.BeginTx(ctx, &sql.TxOptions{
+			Isolation: sql.LevelReadCommitted,
+		})
+		if err != nil {
+			dbt.Fatal(err)
+		}
+
+		_, err = tx1.ExecContext(ctx, "INSERT INTO test VALUES (1)")
+		if err != nil {
+			dbt.Fatal(err)
+		}
+
+		var v int
+		row := tx2.QueryRowContext(ctx, "SELECT COUNT(*) FROM test")
+		if err := row.Scan(&v); err != nil {
+			dbt.Fatal(err)
+		}
+		// Because writer transaction wasn't commited yet, it should be available
+		if v != 0 {
+			dbt.Errorf("expected val to be 0, got %d", v)
+		}
+
+		err = tx1.Commit()
+		if err != nil {
+			dbt.Fatal(err)
+		}
+
+		row = tx2.QueryRowContext(ctx, "SELECT COUNT(*) FROM test")
+		if err := row.Scan(&v); err != nil {
+			dbt.Fatal(err)
+		}
+		// Data written by writer transaction is already commited, it should be selectable
+		if v != 1 {
+			dbt.Errorf("expected val to be 1, got %d", v)
+		}
+		tx2.Commit()
+	})
+}

utils_go18.go

@@ -12,6 +12,7 @@ package mysql
 
 import (
 	"crypto/tls"
+	"database/sql"
 	"database/sql/driver"
 	"errors"
 )
@@ -31,3 +32,18 @@ func namedValueToValue(named []driver.NamedValue) ([]driver.Value, error) {
 	}
 	return dargs, nil
 }
+
+func mapIsolationLevel(level driver.IsolationLevel) (string, error) {
+	switch sql.IsolationLevel(level) {
+	case sql.LevelRepeatableRead:
+		return "REPEATABLE READ", nil
+	case sql.LevelReadCommitted:
+		return "READ COMMITTED", nil
+	case sql.LevelReadUncommitted:
+		return "READ UNCOMMITTED", nil
+	case sql.LevelSerializable:
+		return "SERIALIZABLE", nil
+	default:
+		return "", errors.New("mysql: unsupported isolation level: " + string(level))
+	}
+}

utils_go18_test.go

@@ -0,0 +1,54 @@
+// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
+//
+// Copyright 2017 The Go-MySQL-Driver Authors. All rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build go1.8
+
+package mysql
+
+import (
+	"database/sql"
+	"database/sql/driver"
+	"testing"
+)
+
+func TestIsolationLevelMapping(t *testing.T) {
+
+	data := []struct {
+		level    driver.IsolationLevel
+		expected string
+	}{
+		{
+			level:    driver.IsolationLevel(sql.LevelReadCommitted),
+			expected: "READ COMMITTED",
+		},
+		{
+			level:    driver.IsolationLevel(sql.LevelRepeatableRead),
+			expected: "REPEATABLE READ",
+		},
+		{
+			level:    driver.IsolationLevel(sql.LevelReadUncommitted),
+			expected: "READ UNCOMMITTED",
+		},
+		{
+			level:    driver.IsolationLevel(sql.LevelSerializable),
+			expected: "SERIALIZABLE",
+		},
+	}
+
+	for i, td := range data {
+		if actual, err := mapIsolationLevel(td.level); actual != td.expected || err != nil {
+			t.Fatal(i, td.expected, actual, err)
+		}
+	}
+
+	// check unsupported mapping
+	if actual, err := mapIsolationLevel(driver.IsolationLevel(sql.LevelLinearizable)); actual != "" || err == nil {
+		t.Fatal("Expected error on unsupported isolation level")
+	}
+
+}