SelectValue and SelectRow error if no rows found

fixes #14

connection.go

@@ -29,6 +29,12 @@ type Connection struct {
 	txStatus      byte
 }
 
+type NoRowsFoundError struct {
+	msg string
+}
+
+func (e NoRowsFoundError) Error() string { return e.msg }
+
 func Connect(parameters ConnectionParameters) (c *Connection, err error) {
 	c = new(Connection)
 
@@ -131,12 +137,8 @@ func (c *Connection) SelectFunc(sql string, onDataRow func(*DataRowReader) error
 	panic("Unreachable")
 }
 
-// Null values are not included in rows. However, because maps return the 0 value
-// for missing values this flattens nulls to empty string. If the caller needs to
-// distinguish between a real empty string and a null it can use the comma ok
-// pattern when accessing the map
-func (c *Connection) SelectRows(sql string) (rows []map[string]string, err error) {
-	rows = make([]map[string]string, 0, 8)
+func (c *Connection) SelectRows(sql string) (rows []map[string]interface{}, err error) {
+	rows = make([]map[string]interface{}, 0, 8)
 	onDataRow := func(r *DataRowReader) error {
 		rows = append(rows, c.rxDataRow(r))
 		return nil
@@ -145,25 +147,37 @@ func (c *Connection) SelectRows(sql string) (rows []map[string]string, err error
 	return
 }
 
-// Null values are not included in row. However, because maps return the 0 value
-// for missing values this flattens nulls to empty string. If the caller needs to
-// distinguish between a real empty string and a null it can use the comma ok
-// pattern when accessing the map
-func (c *Connection) SelectRow(sql string) (row map[string]string, err error) {
+func (c *Connection) SelectRow(sql string) (row map[string]interface{}, err error) {
+	var numRowsFound int64
+
 	onDataRow := func(r *DataRowReader) error {
+		numRowsFound++
 		row = c.rxDataRow(r)
 		return nil
 	}
 	err = c.SelectFunc(sql, onDataRow)
+	if err == nil {
+		if numRowsFound == 0 {
+			err = NoRowsFoundError{}
+		}
+	}
 	return
 }
 
 func (c *Connection) SelectValue(sql string) (v interface{}, err error) {
+	var numRowsFound int64
+
 	onDataRow := func(r *DataRowReader) error {
+		numRowsFound++
 		v = r.ReadValue()
 		return nil
 	}
 	err = c.SelectFunc(sql, onDataRow)
+	if err == nil {
+		if numRowsFound == 0 {
+			err = NoRowsFoundError{}
+		}
+	}
 	return
 }
 
@@ -344,16 +358,12 @@ func (c *Connection) rxRowDescription(r *MessageReader) (fields []FieldDescripti
 	return
 }
 
-func (c *Connection) rxDataRow(r *DataRowReader) (row map[string]string) {
+func (c *Connection) rxDataRow(r *DataRowReader) (row map[string]interface{}) {
 	fieldCount := len(r.fields)
-	mr := r.mr
 
-	row = make(map[string]string, fieldCount)
+	row = make(map[string]interface{}, fieldCount)
 	for i := 0; i < fieldCount; i++ {
-		size := mr.ReadInt32()
-		if size > -1 {
-			row[r.fields[i].Name] = mr.ReadByteString(size)
-		}
+		row[r.fields[i].Name] = r.ReadValue()
 	}
 	return
 }

connection_test.go

@@ -36,7 +36,7 @@ func TestConnect(t *testing.T) {
 		t.Error("Backend secret key not stored")
 	}
 
-	var rows []map[string]string
+	var rows []map[string]interface{}
 	rows, err = conn.SelectRows("select current_database()")
 	if err != nil || rows[0]["current_database"] != "pgx_test" {
 		t.Error("Did not connect to specified database (pgx_text)")
@@ -164,12 +164,12 @@ func TestSelectRows(t *testing.T) {
 		t.Error("Received incorrect name")
 	}
 
-	value, presence := rows[0]["position"]
-	if value != "" {
-		t.Error("Should have received empty string for null")
-	}
-	if presence != false {
-		t.Error("Null value shouldn't have been present in map")
+	if value, presence := rows[0]["position"]; presence {
+		if value != nil {
+			t.Error("Should have received nil for null")
+		}
+	} else {
+		t.Error("Null value should have been present in map as nil")
 	}
 }
 
@@ -185,20 +185,17 @@ func TestSelectRow(t *testing.T) {
 		t.Error("Received incorrect name")
 	}
 
-	value, presence := row["position"]
-	if value != "" {
-		t.Error("Should have received empty string for null")
-	}
-	if presence != false {
-		t.Error("Null value shouldn't have been present in map")
+	if value, presence := row["position"]; presence {
+		if value != nil {
+			t.Error("Should have received nil for null")
+		}
+	} else {
+		t.Error("Null value should have been present in map as nil")
 	}
 
-	row, err = conn.SelectRow("select 'Jack' as name where 1=2")
-	if row != nil {
-		t.Error("No matching row should have returned nil")
-	}
-	if err != nil {
-		t.Fatal("Query failed")
+	_, err = conn.SelectRow("select 'Jack' as name where 1=2")
+	if _, ok := err.(NoRowsFoundError); !ok {
+		t.Error("No matching row should have returned NoRowsFoundError")
 	}
 }
 
@@ -224,6 +221,11 @@ func TestConnectionSelectValue(t *testing.T) {
 	test("select 1::int8", int64(1))
 	test("select 1.23::float4", float32(1.23))
 	test("select 1.23::float8", float64(1.23))
+
+	_, err := conn.SelectValue("select 'Jack' as name where 1=2")
+	if _, ok := err.(NoRowsFoundError); !ok {
+		t.Error("No matching row should have returned NoRowsFoundError")
+	}
 }
 
 func TestSelectValues(t *testing.T) {