feat(update): allow clearing values with "" and null on update

Update handlers skipped empty strings and nulls, so a client could not
blank or null out a column. Every key present in the payload now
overwrites the stored value, including "" and null.

- add common.MergeUpdateValues and use it in resolvespec and restheadspec
- add Handler.SetDisallowNulls to skip null values (""still overwrites)
- websocketspec and mqttspec now write only the keys present in the
  payload via SetMap instead of updating the whole zeroed model, which
  clobbered absent fields

pkg/common/update_merge.go

@@ -0,0 +1,23 @@
+package common
+
+// MergeUpdateValues merges the incoming request values into the existing
+// record map (in place) and returns it.
+//
+// Every key present in incoming overwrites the existing value, including empty
+// strings and explicit nulls, so clients can clear a column by sending "" or
+// null. Keys absent from incoming are left untouched.
+//
+// When disallowNulls is true, nil values are skipped and the existing value is
+// kept. Empty strings are still applied.
+func MergeUpdateValues(existing, incoming map[string]interface{}, disallowNulls bool) map[string]interface{} {
+	if existing == nil {
+		existing = make(map[string]interface{}, len(incoming))
+	}
+	for key, newValue := range incoming {
+		if newValue == nil && disallowNulls {
+			continue
+		}
+		existing[key] = newValue
+	}
+	return existing
+}

pkg/common/update_merge_test.go

@@ -0,0 +1,29 @@
+package common
+
+import "testing"
+
+func TestMergeUpdateValues(t *testing.T) {
+	newExisting := func() map[string]interface{} {
+		return map[string]interface{}{"name": "old", "note": "keep", "other": "x"}
+	}
+	incoming := map[string]interface{}{"name": "", "note": nil}
+
+	got := MergeUpdateValues(newExisting(), incoming, false)
+	if got["name"] != "" {
+		t.Errorf("name = %v, want empty string", got["name"])
+	}
+	if v, ok := got["note"]; !ok || v != nil {
+		t.Errorf("note = %v (present=%v), want nil", v, ok)
+	}
+	if got["other"] != "x" {
+		t.Errorf("absent key changed: %v", got["other"])
+	}
+
+	got = MergeUpdateValues(newExisting(), incoming, true)
+	if got["name"] != "" {
+		t.Errorf("disallowNulls: name = %v, want empty string", got["name"])
+	}
+	if got["note"] != "keep" {
+		t.Errorf("disallowNulls: note = %v, want keep", got["note"])
+	}
+}

pkg/mqttspec/handler.go

@@ -45,6 +45,9 @@ type Handler struct {
 	// Started flag
 	started bool
 	mu      sync.RWMutex
+
+	// disallowNulls skips null values in update payloads instead of applying them
+	disallowNulls bool
 }
 
 // NewHandler creates a new MQTT handler
@@ -812,6 +815,14 @@ func (h *Handler) readMultiple(hookCtx *HookContext) (data interface{}, metadata
 }
 
 // create creates a new record
+// SetDisallowNulls controls whether explicit null values in update payloads are
+// ignored. By default a key present in the payload overwrites the stored value,
+// including "" and null. When true, null values are skipped and the existing
+// value is kept ("" still overwrites).
+func (h *Handler) SetDisallowNulls(disallow bool) {
+	h.disallowNulls = disallow
+}
+
 func (h *Handler) create(hookCtx *HookContext) (interface{}, error) {
 	// Marshal and unmarshal data into model
 	dataBytes, err := json.Marshal(hookCtx.Data)
@@ -840,25 +851,33 @@ func (h *Handler) create(hookCtx *HookContext) (interface{}, error) {
 
 // update updates an existing record
 func (h *Handler) update(hookCtx *HookContext) (interface{}, error) {
-	// Marshal and unmarshal data into model
+	// Convert request data to a map
-	dataBytes, err := json.Marshal(hookCtx.Data)
+	var updates map[string]interface{}
-	if err != nil {
+	if m, ok := hookCtx.Data.(map[string]interface{}); ok {
-		return nil, fmt.Errorf("failed to marshal data: %w", err)
+		updates = m
+	} else {
+		dataBytes, err := json.Marshal(hookCtx.Data)
+		if err != nil {
+			return nil, fmt.Errorf("failed to marshal data: %w", err)
+		}
+		if err := json.Unmarshal(dataBytes, &updates); err != nil {
+			return nil, fmt.Errorf("failed to unmarshal data into map: %w", err)
+		}
 	}
 
-	if err := json.Unmarshal(dataBytes, hookCtx.ModelPtr); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal data into model: %w", err)
-	}
-
-	// Update record
-	query := h.db.NewUpdate().Model(hookCtx.ModelPtr).Table(hookCtx.TableName)
-
-	// Add ID filter
 	pkName := reflection.GetPrimaryKeyName(hookCtx.Model)
-	query = query.Where(fmt.Sprintf("%s = ?", pkName), hookCtx.ID)
 
-	if _, err := query.Exec(hookCtx.Context); err != nil {
+	// Only the keys present in the request are written. "" and null overwrite
-		return nil, fmt.Errorf("failed to update record: %w", err)
+	// the stored value unless disallowNulls is set, in which case null is skipped.
+	values := common.MergeUpdateValues(make(map[string]interface{}, len(updates)), updates, h.disallowNulls)
+
+	if len(values) > 0 {
+		query := h.db.NewUpdate().Table(hookCtx.TableName).SetMap(values).
+			Where(fmt.Sprintf("%s = ?", common.QuoteIdent(pkName)), hookCtx.ID)
+
+		if _, err := query.Exec(hookCtx.Context); err != nil {
+			return nil, fmt.Errorf("failed to update record: %w", err)
+		}
 	}
 
 	// Fetch updated record

pkg/resolvespec/handler.go

@@ -32,6 +32,7 @@ type Handler struct {
 	fallbackHandler  FallbackHandler
 	openAPIGenerator func() (string, error)
 	defaultSort      map[string][]common.SortOption
+	disallowNulls    bool
 }
 
 // NewHandler creates a new API handler with database and registry abstractions
@@ -52,6 +53,14 @@ func (h *Handler) Hooks() *HookRegistry {
 	return h.hooks
 }
 
+// SetDisallowNulls controls whether explicit null values in update payloads are
+// ignored. By default a key present in the payload overwrites the stored value,
+// including "" and null. When true, null values are skipped and the existing
+// value is kept ("" still overwrites).
+func (h *Handler) SetDisallowNulls(disallow bool) {
+	h.disallowNulls = disallow
+}
+
 // SetFallbackHandler sets a fallback handler to be called when no model is found
 // If not set, the handler will simply return (pass through to next route)
 func (h *Handler) SetFallbackHandler(fallback FallbackHandler) {
@@ -1236,21 +1245,8 @@ func (h *Handler) handleUpdate(ctx context.Context, w common.ResponseWriter, url
 				return fmt.Errorf("error unmarshaling existing record: %w", err)
 			}
 
-			// Merge only non-null and non-empty values from the incoming request into the existing record
+			// Overwrite with every key present in the request (including "" and null unless disallowed)
-			for key, newValue := range updates {
+			common.MergeUpdateValues(existingMap, updates, h.disallowNulls)
-				// Skip if the value is nil
-				if newValue == nil {
-					continue
-				}
-
-				// Skip if the value is an empty string
-				if strVal, ok := newValue.(string); ok && strVal == "" {
-					continue
-				}
-
-				// Update the existing map with the new value
-				existingMap[key] = newValue
-			}
 
 			// Build update query with merged data
 			query := tx.NewUpdate().Table(tableName).SetMap(existingMap)
@@ -1421,16 +1417,8 @@ func (h *Handler) handleUpdate(ctx context.Context, w common.ResponseWriter, url
 						item = modifiedData
 					}
 
-					// Merge only non-null and non-empty values
+					// Overwrite with every key present in the request (including "" and null unless disallowed)
-					for key, newValue := range item {
+					common.MergeUpdateValues(existingMap, item, h.disallowNulls)
-						if newValue == nil {
-							continue
-						}
-						if strVal, ok := newValue.(string); ok && strVal == "" {
-							continue
-						}
-						existingMap[key] = newValue
-					}
 
 					txQuery := tx.NewUpdate().Table(tableName).SetMap(existingMap).Where(fmt.Sprintf("%s = ?", common.QuoteIdent(pkName)), itemID)
 					if _, err := txQuery.Exec(ctx); err != nil {
@@ -1578,16 +1566,8 @@ func (h *Handler) handleUpdate(ctx context.Context, w common.ResponseWriter, url
 							itemMap = modifiedData
 						}
 
-						// Merge only non-null and non-empty values
+						// Overwrite with every key present in the request (including "" and null unless disallowed)
-						for key, newValue := range itemMap {
+						common.MergeUpdateValues(existingMap, itemMap, h.disallowNulls)
-							if newValue == nil {
-								continue
-							}
-							if strVal, ok := newValue.(string); ok && strVal == "" {
-								continue
-							}
-							existingMap[key] = newValue
-						}
 
 						txQuery := tx.NewUpdate().Table(tableName).SetMap(existingMap).Where(fmt.Sprintf("%s = ?", common.QuoteIdent(pkName)), itemID)
 						if _, err := txQuery.Exec(ctx); err != nil {

pkg/restheadspec/handler.go

@@ -33,6 +33,7 @@ type Handler struct {
 	fallbackHandler  FallbackHandler
 	openAPIGenerator func() (string, error)
 	defaultSort      map[string][]common.SortOption
+	disallowNulls    bool
 }
 
 // NewHandler creates a new API handler with database and registry abstractions
@@ -59,6 +60,14 @@ func (h *Handler) Hooks() *HookRegistry {
 	return h.hooks
 }
 
+// SetDisallowNulls controls whether explicit null values in update payloads are
+// ignored. By default a key present in the payload overwrites the stored value,
+// including "" and null. When true, null values are skipped and the existing
+// value is kept ("" still overwrites).
+func (h *Handler) SetDisallowNulls(disallow bool) {
+	h.disallowNulls = disallow
+}
+
 // SetFallbackHandler sets a fallback handler to be called when no model is found
 // If not set, the handler will simply return (pass through to next route)
 func (h *Handler) SetFallbackHandler(fallback FallbackHandler) {
@@ -1597,21 +1606,8 @@ func (h *Handler) handleUpdate(ctx context.Context, w common.ResponseWriter, id
 			nestedRelations = relations
 		}
 
-		// Merge only non-null and non-empty values from the incoming request into the existing record
+		// Overwrite with every key present in the request (including "" and null unless disallowed)
-		for key, newValue := range dataMap {
+		common.MergeUpdateValues(existingMap, dataMap, h.disallowNulls)
-			// Skip if the value is nil
-			if newValue == nil {
-				continue
-			}
-
-			// Skip if the value is an empty string
-			if strVal, ok := newValue.(string); ok && strVal == "" {
-				continue
-			}
-
-			// Update the existing map with the new value
-			existingMap[key] = newValue
-		}
 
 		// Ensure ID is in the data map for the update
 		existingMap[pkName] = targetID

pkg/websocketspec/handler.go

@@ -38,6 +38,9 @@ type Handler struct {
 	subscriptionManager *SubscriptionManager
 	upgrader            websocket.Upgrader
 	ctx                 context.Context
+
+	// disallowNulls skips null values in update payloads instead of applying them
+	disallowNulls bool
 }
 
 // NewHandler creates a new WebSocket handler
@@ -682,6 +685,14 @@ func (h *Handler) readMultiple(hookCtx *HookContext) (data interface{}, metadata
 	return hookCtx.ModelPtr, metadata, nil
 }
 
+// SetDisallowNulls controls whether explicit null values in update payloads are
+// ignored. By default a key present in the payload overwrites the stored value,
+// including "" and null. When true, null values are skipped and the existing
+// value is kept ("" still overwrites).
+func (h *Handler) SetDisallowNulls(disallow bool) {
+	h.disallowNulls = disallow
+}
+
 func (h *Handler) create(hookCtx *HookContext) (interface{}, error) {
 	// Marshal and unmarshal data into model
 	dataBytes, err := json.Marshal(hookCtx.Data)
@@ -709,25 +720,33 @@ func (h *Handler) create(hookCtx *HookContext) (interface{}, error) {
 }
 
 func (h *Handler) update(hookCtx *HookContext) (interface{}, error) {
-	// Marshal and unmarshal data into model
+	// Convert request data to a map
-	dataBytes, err := json.Marshal(hookCtx.Data)
+	var updates map[string]interface{}
-	if err != nil {
+	if m, ok := hookCtx.Data.(map[string]interface{}); ok {
-		return nil, fmt.Errorf("failed to marshal data: %w", err)
+		updates = m
+	} else {
+		dataBytes, err := json.Marshal(hookCtx.Data)
+		if err != nil {
+			return nil, fmt.Errorf("failed to marshal data: %w", err)
+		}
+		if err := json.Unmarshal(dataBytes, &updates); err != nil {
+			return nil, fmt.Errorf("failed to unmarshal data into map: %w", err)
+		}
 	}
 
-	if err := json.Unmarshal(dataBytes, hookCtx.ModelPtr); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal data into model: %w", err)
-	}
-
-	// Update record
-	query := h.db.NewUpdate().Model(hookCtx.ModelPtr).Table(hookCtx.TableName)
-
-	// Add ID filter
 	pkName := reflection.GetPrimaryKeyName(hookCtx.Model)
-	query = query.Where(fmt.Sprintf("%s = ?", pkName), hookCtx.ID)
 
-	if _, err := query.Exec(hookCtx.Context); err != nil {
+	// Only the keys present in the request are written. "" and null overwrite
-		return nil, fmt.Errorf("failed to update record: %w", err)
+	// the stored value unless disallowNulls is set, in which case null is skipped.
+	values := common.MergeUpdateValues(make(map[string]interface{}, len(updates)), updates, h.disallowNulls)
+
+	if len(values) > 0 {
+		query := h.db.NewUpdate().Table(hookCtx.TableName).SetMap(values).
+			Where(fmt.Sprintf("%s = ?", common.QuoteIdent(pkName)), hookCtx.ID)
+
+		if _, err := query.Exec(hookCtx.Context); err != nil {
+			return nil, fmt.Errorf("failed to update record: %w", err)
+		}
 	}
 
 	// Fetch updated record