Add support for unmarshalling embedded structs with relationships

This commit adds better support for unmarshaling embedded structs that contain relationship fields

jsonapi_test.go

@@ -15,11 +15,16 @@ var (
 	authorBWithMeta = Author{ID: "2", Name: "B", Meta: map[string]any{"count": 10.0}}
 
 	// comments
-	commentA           = Comment{ID: "1", Body: "A"}
-	commentB           = Comment{ID: "2", Body: "B"}
-	commentAWithAuthor = Comment{ID: "1", Body: "A", Author: &authorA}
-	commentArchived    = Comment{ID: "1", Body: "A", Archived: true}
-	commentsAB         = []*Comment{&commentA, &commentB}
+	commentA              = Comment{ID: "1", Body: "A"}
+	commentB              = Comment{ID: "2", Body: "B"}
+	commentAWithAuthor    = Comment{ID: "1", Body: "A", Author: &authorA}
+	commentArchived       = Comment{ID: "1", Body: "A", Archived: true}
+	commentsAB            = []*Comment{&commentA, &commentB}
+	commentEmbeddedFields = CommentFields{Body: "A", Author: Author{ID: "1"}}
+	commentEmbedded       = CommentEmbedded{ID: "1", CommentFields: commentEmbeddedFields}
+
+	commentEmbeddedFieldsPointer = CommentFieldsPointer{Body: "A", Author: &Author{ID: "1"}}
+	commentEmbeddedPointer       = CommentEmbeddedPointer{ID: "1", CommentFieldsPointer: commentEmbeddedFieldsPointer}
 
 	// articles
 	articleA        = Article{ID: "1", Title: "A"}
@@ -157,6 +162,7 @@ var (
 	articleNullWithToplevelMetaBody       = `{"data":null,"meta":{"foo":"bar"}}`
 	articleEmptyArrayWithToplevelMetaBody = `{"data":[],"meta":{"foo":"bar"}}`
 	articleEmbeddedBody                   = `{"data":{"type":"articles","id":"1","attributes":{"title":"A","lastModified":"1989-06-15T00:00:00Z"}}}`
+	commentEmbeddedBody                   = `{"data":{"id":"1","type":"comments","attributes":{"body":"A"},"relationships":{"author":{"data":{"id":"1","type":"author"}}}}}`
 
 	// articles with relationships bodies
 	articleRelatedInvalidEmptyRelationshipBody  = `{"data":{"id":"1","type":"articles","attributes":{"title":"A"},"relationships":{"author":{}}}}`
@@ -454,6 +460,28 @@ type Metadata struct {
 	LastModified time.Time `jsonapi:"attribute" json:"lastModified"`
 }
 
+type CommentFields struct {
+	Body     string `jsonapi:"attribute" json:"body"`
+	Archived bool   `jsonapi:"attribute" json:"archived,omitempty"`
+	Author   Author `jsonapi:"relationship" json:"author,omitempty"`
+}
+
+type CommentFieldsPointer struct {
+	Body     string  `jsonapi:"attribute" json:"body"`
+	Archived bool    `jsonapi:"attribute" json:"archived,omitempty"`
+	Author   *Author `jsonapi:"relationship" json:"author,omitempty"`
+}
+
+type CommentEmbedded struct {
+	ID string `jsonapi:"primary,comments"`
+	CommentFields
+}
+
+type CommentEmbeddedPointer struct {
+	ID string `jsonapi:"primary,comments"`
+	CommentFieldsPointer
+}
+
 type ArticleEmbedded struct {
 	Metadata
 

unmarshal.go

@@ -170,18 +170,18 @@ func (ro *resourceObject) unmarshal(v any, m *Unmarshaler) error {
 		return &TypeError{Actual: vt.String(), Expected: []string{"struct"}}
 	}
 
-	if err := ro.unmarshalFields(v, m); err != nil {
+	rv := derefValue(reflect.ValueOf(v))
+	rt := reflect.TypeOf(rv.Interface())
+	if err := ro.unmarshalFields(v, rv, rt, m); err != nil {
 		return err
 	}
 
 	return ro.unmarshalAttributes(v)
 }
 
 // unmarshalFields unmarshals a resource object into all non-attribute struct fields
-func (ro *resourceObject) unmarshalFields(v any, m *Unmarshaler) error {
+func (ro *resourceObject) unmarshalFields(v any, rv reflect.Value, rt reflect.Type, m *Unmarshaler) error {
 	setPrimary := false
-	rv := derefValue(reflect.ValueOf(v))
-	rt := reflect.TypeOf(rv.Interface())
 
 	for i := 0; i < rv.NumField(); i++ {
 		fv := rv.Field(i)
@@ -191,6 +191,15 @@ func (ro *resourceObject) unmarshalFields(v any, m *Unmarshaler) error {
 		if err != nil {
 			return err
 		}
+		// If there is an embedded struct we want to process the fields in that struct recursively
+		// only if there isn't a relationship defined on the field.
+		if fv.Kind() == reflect.Struct && jsonapiTag == nil {
+			if err := ro.unmarshalFields(v, fv, reflect.TypeOf(fv.Interface()), m); err != nil {
+				return err
+			}
+			continue
+		}
+
 		if jsonapiTag == nil {
 			continue
 		}

unmarshal_test.go

@@ -446,6 +446,27 @@ func TestUnmarshal(t *testing.T) {
 			},
 			expect:      &Article{},
 			expectError: ErrErrorUnmarshalingNotImplemented,
+		}, {
+			description: "CommentEmbedded",
+			given:       commentEmbeddedBody,
+			do: func(body []byte) (any, error) {
+				var a CommentEmbedded
+				err := Unmarshal(body, &a)
+				return &a, err
+			},
+			expect:      &commentEmbedded,
+			expectError: nil,
+		},
+		{
+			description: "CommentEmbeddedPointer",
+			given:       commentEmbeddedBody,
+			do: func(body []byte) (any, error) {
+				var a CommentEmbeddedPointer
+				err := Unmarshal(body, &a)
+				return &a, err
+			},
+			expect:      &commentEmbeddedPointer,
+			expectError: nil,
 		},
 	}