feat: add GetOrInheritFieldValue function for hierarchical field retrieval

docs/02-client/06-otherfunctions.md

@@ -6,6 +6,56 @@ Another thing you might want to know is the content type of an entry with a give
 (cc *ContentfulClient) GetContentTypeOfID(ctx, ID string) (contentType string)
 ```
 
+## Field inheritance
+
+When working with hierarchical content structures, you may need to retrieve field values that can be inherited from parent entries. The `GetOrInheritFieldValue` function provides this functionality:
+
+```go
+func GetOrInheritFieldValue(ctx context.Context, contentfulShop *ContentfulClient, entryID string, field string, parentContentTypes []string, locale Locale) (any, error)
+```
+
+This function retrieves a field value from a GenericEntry, traversing up the full parent hierarchy if the field is not found in the current entry. It's particularly useful for content types that have parent-child relationships where certain fields should be inherited from parent entries.
+
+### Parameters
+
+- `ctx`: Context for the operation
+- `contentfulShop`: The ContentfulClient instance
+- `entryID`: The ID of the entry to start the search from
+- `field`: The field name to retrieve
+- `parentContentTypes`: List of content type IDs that should be considered as valid parents
+- `locale`: The locale to retrieve the field value in
+
+### Return value
+
+Returns the field value as `any` type, or an error if:
+- The entry cannot be retrieved
+- A circular reference is detected in the parent hierarchy
+- The field is not found in any parent entry
+- Any parent entry cannot be retrieved
+
+### Example usage
+
+```go
+ctx := context.Background()
+parentContentTypes := []string{"category", "section"}
+
+// Try to get the "theme" field from the current entry or inherit it from parents
+theme, err := GetOrInheritFieldValue(ctx, cc, "my-entry-id", "theme", parentContentTypes, contentful.DefaultLocale)
+if err != nil {
+    log.Printf("Theme not found: %v", err)
+} else {
+    log.Printf("Theme value: %v", theme)
+}
+```
+
+### Important notes
+
+- The function first attempts to get the field value from the current entry
+- If not found, it recursively traverses up the parent hierarchy
+- Circular references are detected and will return an error to prevent infinite loops
+- The function respects the locale parameter for localized field values
+- Only entries with content types specified in `parentContentTypes` are considered as valid parents
+
 ## Caveats and limitations
 
 - Avoid creating content types that have field IDs equal to reserved Go words (e.g. "type").

erm/templates/contentful_vo_lib.gotmpl

@@ -568,7 +568,52 @@ func (ref EntryReference) GetParents(ctx context.Context, contentType ...string)
 		}
 		return candidateParents, nil
 	}
-	return nil, errors.New("GetParents: reference VO and CC are both nil")
+}
+
+func GetOrInheritFieldValue(ctx context.Context, contentfulShop *ContentfulClient, entryID string, field string, parentContentTypes []string, locale Locale) (any, error) {
+	entry, err := contentfulShop.GetGenericEntry(entryID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get entry %s: %v", entryID, err)
+	}
+
+	// Try to get the field value from the current entry first
+	val, err := entry.FieldAsAny(field, locale)
+	if err == nil {
+		return val, nil
+	}
+
+	return inheritFieldValueRecursive(ctx, contentfulShop, entry, field, parentContentTypes, locale, make(map[string]bool))
+}
+
+func inheritFieldValueRecursive(ctx context.Context, contentfulShop *ContentfulClient, entry *GenericEntry, field string, parentContentTypes []string, locale Locale, visited map[string]bool) (any, error) {
+	if visited[entry.Sys.ID] {
+		return nil, fmt.Errorf("circular reference detected for entry %s", entry.Sys.ID)
+	}
+	visited[entry.Sys.ID] = true
+
+	parentRefs, err := commonGetParents(ctx, entry.CC, entry.Sys.ID, parentContentTypes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get parents for entry %s: %v", entry.Sys.ID, err)
+	}
+
+	for _, parentRef := range parentRefs {
+		parentEntry, err := entry.CC.GetGenericEntry(parentRef.ID)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get parent entry %s: %v", parentRef.ID, err)
+		}
+
+		val, err := parentEntry.FieldAsAny(field, locale)
+		if err == nil {
+			return val, nil
+		}
+
+		inheritedVal, err := inheritFieldValueRecursive(ctx, contentfulShop, parentEntry, field, parentContentTypes, locale, visited)
+		if err == nil {
+			return inheritedVal, nil
+		}
+	}
+
+	return nil, ErrNotSet
 }
 
 func HtmlToRichText(htmlSrc string) *RichTextNode {

test/testapi/gocontentfulvolib.go

@@ -597,7 +597,52 @@ func (ref EntryReference) GetParents(ctx context.Context, contentType ...string)
 		}
 		return candidateParents, nil
 	}
-	return nil, errors.New("GetParents: reference VO and CC are both nil")
+}
+
+func GetOrInheritFieldValue(ctx context.Context, contentfulShop *ContentfulClient, entryID string, field string, parentContentTypes []string, locale Locale) (any, error) {
+	entry, err := contentfulShop.GetGenericEntry(entryID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get entry %s: %v", entryID, err)
+	}
+
+	// Try to get the field value from the current entry first
+	val, err := entry.FieldAsAny(field, locale)
+	if err == nil {
+		return val, nil
+	}
+
+	return inheritFieldValueRecursive(ctx, contentfulShop, entry, field, parentContentTypes, locale, make(map[string]bool))
+}
+
+func inheritFieldValueRecursive(ctx context.Context, contentfulShop *ContentfulClient, entry *GenericEntry, field string, parentContentTypes []string, locale Locale, visited map[string]bool) (any, error) {
+	if visited[entry.Sys.ID] {
+		return nil, fmt.Errorf("circular reference detected for entry %s", entry.Sys.ID)
+	}
+	visited[entry.Sys.ID] = true
+
+	parentRefs, err := commonGetParents(ctx, entry.CC, entry.Sys.ID, parentContentTypes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get parents for entry %s: %v", entry.Sys.ID, err)
+	}
+
+	for _, parentRef := range parentRefs {
+		parentEntry, err := entry.CC.GetGenericEntry(parentRef.ID)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get parent entry %s: %v", parentRef.ID, err)
+		}
+
+		val, err := parentEntry.FieldAsAny(field, locale)
+		if err == nil {
+			return val, nil
+		}
+
+		inheritedVal, err := inheritFieldValueRecursive(ctx, contentfulShop, parentEntry, field, parentContentTypes, locale, visited)
+		if err == nil {
+			return inheritedVal, nil
+		}
+	}
+
+	return nil, ErrNotSet
 }
 
 func HtmlToRichText(htmlSrc string) *RichTextNode {