Add TransationIso

fixes #5

connection.go

@@ -416,7 +416,22 @@ func (c *Connection) Execute(sql string, arguments ...interface{}) (commandTag s
 }
 
 func (c *Connection) Transaction(f func() bool) (committed bool, err error) {
-	if _, err = c.Execute("begin"); err != nil {
+	return c.transaction("", f)
+}
+
+func (c *Connection) TransactionIso(isoLevel string, f func() bool) (committed bool, err error) {
+	return c.transaction(isoLevel, f)
+}
+
+func (c *Connection) transaction(isoLevel string, f func() bool) (committed bool, err error) {
+	var beginSql string
+	if isoLevel == "" {
+		beginSql = "begin"
+	} else {
+		beginSql = fmt.Sprintf("begin isolation level %s", isoLevel)
+	}
+
+	if _, err = c.Execute(beginSql); err != nil {
 		return
 	}
 	defer func() {

connection_test.go

@@ -536,3 +536,24 @@ func TestTransaction(t *testing.T) {
 		}
 	}()
 }
+
+func TestTransactionIso(t *testing.T) {
+	conn, err := Connect(*defaultConnectionParameters)
+	if err != nil {
+		t.Fatalf("Unable to establish connection: %v", err)
+	}
+	defer conn.Close()
+
+	isoLevels := []string{"serializable", "repeatable read", "read committed", "read uncommitted"}
+	for _, iso := range isoLevels {
+		_, err := conn.TransactionIso(iso, func() bool {
+			if level := mustSelectValue(t, conn, "select current_setting('transaction_isolation')"); level != iso {
+				t.Errorf("Expected to be in isolation level %v but was %v", iso, level)
+			}
+			return true
+		})
+		if err != nil {
+			t.Fatalf("Unexpected transaction failure: %v", err)
+		}
+	}
+}