update docs

README.md

@@ -77,6 +77,44 @@ func main() {
   - `UPDATE`
   - `DELETE`
 
+## Transaction support
+
+`godynamo` supports transactions that consist of write statements (e.g. `INSERT`, `UPDATE` and `DELETE`) since [v0.2.0](RELEASE-NOTES.md). Please note the following:
+
+- Any limitation set by [DynamoDB/PartiQL](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-reference.multiplestatements.transactions.html) will apply.
+- [Table](SQL_TABLE.md) and [Index](SQL_INDEX.md) statements are not supported.
+- `UPDATE`/`DELETE` with `RETURNING` and `SELECT` statements are not supported.
+
+Example:
+```go
+tx, err := db.Begin()
+if err != nil {
+	panic(err)
+}
+defer tx.Rollback()
+result1, _ := tx.Exec(`INSERT INTO "tbltest" VALUE {'app': ?, 'user': ?, 'active': ?}`, "app0", "user1", true)
+result2, _ := tx.Exec(`INSERT INTO "tbltest" VALUE {'app': ?, 'user': ?, 'duration': ?}`, "app0", "user2", 1.23)
+err = tx.Commit()
+if err != nil {
+	panic(err)
+}
+rowsAffected1, err1 := fmt.Println(result1.RowsAffected())
+if err1 != nil {
+	panic(err1)
+}
+fmt.Println("RowsAffected:", rowsAffected1) // output "RowsAffected: 1"
+
+rowsAffected2, err2 := fmt.Println(result2.RowsAffected())
+if err2 != nil {
+	panic(err2)
+}
+fmt.Println("RowsAffected:", rowsAffected2) // output "RowsAffected: 1"
+```
+
+> If a statement's condition check fails (e.g. deleting non-existing item), the whole transaction will also fail. This behaviour is different from executing statements in non-transactional mode where failed condition check results in `0` affected row without error.
+>
+> You can use [`EXISTS` function](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/ql-functions.exists.html) for condition checking.
+
 ## License
 
 MIT - See [LICENSE.md](LICENSE.md).

stmt_document.go

@@ -101,6 +101,9 @@ func (s *StmtSelect) Query(values []driver.Value) (driver.Rows, error) {
 // @Available since v0.2.0
 func (s *StmtSelect) QueryContext(ctx context.Context, values []driver.NamedValue) (driver.Rows, error) {
 	outputFn, err := s.conn.executeContext(ctx, s.Stmt, values)
+	if err == ErrInTx {
+		return &TxResultResultSet{wrap: ResultResultSet{err: err}, outputFn: outputFn}, nil
+	}
 	result := &ResultResultSet{stmtOutput: outputFn()}
 	if err == nil {
 		result.init()

tx.go

@@ -1,7 +1,9 @@
 package godynamo
 
 import (
+	"database/sql/driver"
 	"fmt"
+	"reflect"
 )
 
 // TxResultNoResultSet is transaction-aware version of ResultNoResultSet.
@@ -33,6 +35,62 @@ func (t *TxResultNoResultSet) RowsAffected() (int64, error) {
 	return t.affectedRows, nil
 }
 
+// TxResultResultSet is transaction-aware version of ResultResultSet.
+//
+// @Available since v0.2.0
+type TxResultResultSet struct {
+	wrap      ResultResultSet
+	hasOutput bool
+	outputFn  executeStatementOutputWrapper
+}
+
+func (r *TxResultResultSet) checkOutput() {
+	if !r.hasOutput {
+		r.wrap.stmtOutput = r.outputFn()
+		fmt.Println("DEBUG", r.wrap.stmtOutput)
+		if r.wrap.stmtOutput != nil {
+			r.wrap.err = nil
+			r.hasOutput = true
+			r.wrap.init()
+		}
+	}
+}
+
+// Columns implements driver.Rows/Columns.
+func (r *TxResultResultSet) Columns() []string {
+	r.checkOutput()
+	return r.wrap.Columns()
+}
+
+// ColumnTypeScanType implements driver.RowsColumnTypeScanType/ColumnTypeScanType
+func (r *TxResultResultSet) ColumnTypeScanType(index int) reflect.Type {
+	r.checkOutput()
+	return r.wrap.ColumnTypeScanType(index)
+}
+
+// ColumnTypeDatabaseTypeName implements driver.RowsColumnTypeDatabaseTypeName/ColumnTypeDatabaseTypeName
+func (r *TxResultResultSet) ColumnTypeDatabaseTypeName(index int) string {
+	r.checkOutput()
+	return r.wrap.ColumnTypeDatabaseTypeName(index)
+}
+
+// Close implements driver.Rows/Close.
+func (r *TxResultResultSet) Close() error {
+	r.checkOutput()
+	if !r.hasOutput {
+		return ErrInTx
+	}
+	return nil
+}
+
+// Next implements driver.Rows/Next.
+func (r *TxResultResultSet) Next(dest []driver.Value) error {
+	r.checkOutput()
+	return r.wrap.Next(dest)
+}
+
+/*----------------------------------------------------------------------*/
+
 // Tx is AWS DynamoDB implementation of driver.Tx.
 //
 // @Available since v0.2.0