framestruct: Fix wrong conversion even if the first column contains null values (#601)

Author: skurfuerst

data/framestruct/converter.go

@@ -129,6 +129,7 @@ func (c *converter) convertStruct(field reflect.Value, fieldName string) error {
 
 func (c *converter) convertSlice(s reflect.Value, prefix string) error {
 	for i := 0; i < s.Len(); i++ {
+		c.maxLen++
 		v := s.Index(i)
 		switch v.Kind() {
 		case reflect.Map:
@@ -259,9 +260,6 @@ func (c *converter) convertField(v reflect.Value, fieldName string) (interface{}
 
 func (c *converter) appendToField(name string, value interface{}) {
 	c.fields[name].Append(value)
-	if c.fields[name].Len() > c.maxLen {
-		c.maxLen++
-	}
 }
 
 func (c *converter) createFrame(name string) *data.Frame {

data/framestruct/converter_test.go

@@ -312,6 +312,71 @@ func TestSlices(t *testing.T) {
 		require.Equal(t, "baz1", fromPointer(frame.Fields[2].At(1)))
 	})
 
+	t.Run("it flattens a slice of maps that are different sizes even if col0 is not fully-defined", func(t *testing.T) {
+		maps := []map[string]interface{}{
+			{
+				"Thing2": int32(36),
+			},
+			{
+				"Thing1": "foo1",
+				"Thing3": "baz1",
+			},
+		}
+
+		// result
+		// | Thing1 | Thing2 | Thing3 |
+		// |--------+--------+--------|
+		// | nil    | 36     | nil    |
+		// | foo1   | nil    | baz1   |
+
+		frame, err := framestruct.ToDataFrame("results", maps)
+		require.Nil(t, err)
+
+		require.Len(t, frame.Fields, 3)
+		require.Equal(t, 2, frame.Fields[0].Len())
+		require.Equal(t, 2, frame.Fields[1].Len())
+		require.Equal(t, 2, frame.Fields[2].Len())
+
+		require.Nil(t, frame.Fields[0].At(0))
+		require.Equal(t, "foo1", fromPointer(frame.Fields[0].At(1)))
+
+		require.Equal(t, int32(36), fromPointer(frame.Fields[1].At(0)))
+		require.Nil(t, frame.Fields[1].At(1))
+
+		require.Nil(t, frame.Fields[2].At(0))
+		require.Equal(t, "baz1", fromPointer(frame.Fields[2].At(1)))
+	})
+
+	t.Run("it flattens a slice of maps that are different sizes even if col0 is not fully-defined (minimal)s", func(t *testing.T) {
+		maps := []map[string]interface{}{
+			{
+				"b": true,
+			},
+			{
+				"a": true,
+			},
+		}
+
+		// result
+		// | a    | b    |
+		// |------+------|
+		// | nil  | true |
+		// | true | nil  |
+
+		frame, err := framestruct.ToDataFrame("results", maps)
+		require.Nil(t, err)
+
+		require.Len(t, frame.Fields, 2)
+		require.Equal(t, 2, frame.Fields[0].Len())
+		require.Equal(t, 2, frame.Fields[1].Len())
+
+		require.Nil(t, frame.Fields[0].At(0))
+		require.Equal(t, true, fromPointer(frame.Fields[0].At(1)))
+
+		require.Equal(t, true, fromPointer(frame.Fields[1].At(0)))
+		require.Nil(t, frame.Fields[1].At(1))
+	})
+
 	t.Run("it flattens a slice of maps that contains nil values", func(t *testing.T) {
 		// like the testcase above, just with "nil" instead of non-defined map keys.
 		maps := []map[string]interface{}{