refac: atomic merge, lost-update race, RunPurge cost, duplicated walks

internal/domain/contenttype/fieldSchema.go

@@ -115,6 +115,21 @@ func (f Field) validDefault() bool {
 	return !f.Unique && f.Violation(f.Default) == ""
 }
 
+type MediaRef struct {
+	Field Field
+	ID    uint32
+}
+
+func MediaRefs(fields []Field, data map[string]any) []MediaRef {
+	var refs []MediaRef
+	for _, field := range MediaFields(fields) {
+		if id, set := MediaID(data[field.Key]); set {
+			refs = append(refs, MediaRef{Field: field, ID: id})
+		}
+	}
+	return refs
+}
+
 func MediaFields(fields []Field) []Field {
 	var media []Field
 	for _, field := range fields {