feat(spanner): add methods to return Row fields (#8953)

* feat(spanner): add code and tests

* feat(spanner): code fix

---------

Co-authored-by: rahul2393 <irahul@google.com>

spanner/row.go

@@ -174,6 +174,22 @@ func (r *Row) ColumnNames() []string {
 	return n
 }
 
+// ColumnType returns the Cloud Spanner Type of column i, or nil for invalid column.
+func (r *Row) ColumnType(i int) *sppb.Type {
+	if i < 0 || i >= len(r.fields) {
+		return nil
+	}
+	return r.fields[i].Type
+}
+
+// ColumnValue returns the Cloud Spanner Value of column i, or nil for invalid column.
+func (r *Row) ColumnValue(i int) *proto3.Value {
+	if i < 0 || i >= len(r.vals) {
+		return nil
+	}
+	return r.vals[i]
+}
+
 // errColIdxOutOfRange returns error for requested column index is out of the
 // range of the target Row's columns.
 func errColIdxOutOfRange(i int, r *Row) error {

spanner/row_test.go

@@ -1909,6 +1909,30 @@ func TestColumnNameAndIndex(t *testing.T) {
 	}
 }
 
+// Test helpers for getting column type and value.
+func TestColumnTypeAndValue(t *testing.T) {
+	// Test Row.ColumnType()
+	for i, col := range row.fields {
+		if ct := row.ColumnType(i); ct != col.Type {
+			t.Errorf("row.ColumnType(%v) returns %q, want %q", i, ct, col.Type)
+		}
+	}
+	// Test Row.ColumnValue()
+	for i, val := range row.vals {
+		if cv := row.ColumnValue(i); cv != val {
+			t.Errorf("row.ColumnValue(%v) returns %q, want %q", i, cv, val)
+		}
+	}
+	// Test Row.ColumnType on empty Row.
+	if ct := (&Row{}).ColumnType(0); ct != nil {
+		t.Errorf("empty_row.ColumnType(%v) returns %v, want %v", 0, ct, nil)
+	}
+	// Test Row.ColumnValue on empty Row.
+	if cv := (&Row{}).ColumnValue(0); cv != nil {
+		t.Errorf("empty_row.ColumnValue(%v) returns %v, want %v", 0, cv, nil)
+	}
+}
+
 func TestNewRow(t *testing.T) {
 	for _, test := range []struct {
 		names   []string