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/middleware/README.md

@@ -449,11 +449,13 @@ no per-client labels so cardinality stays bounded.
 | Metric | Type | Meaning |
 |---|---|---|
 | `clientqueue_requests_total{result}` | counter | `immediate`, `queued`, `rejected_full`, `timeout`, `canceled` |
+| `clientqueue_enqueued_total` | counter | requests ever placed in a wait queue, whatever happened next (ran, timed out, cancelled) |
 | `clientqueue_wait_seconds` | histogram | wait for a slot; 0 for requests that ran immediately |
 | `clientqueue_wait_max_seconds` | gauge | longest wait since process start |
 | `clientqueue_burst_size` | histogram | peak outstanding requests per client busy period |
 | `clientqueue_burst_max` | gauge | largest burst since process start |
 | `clientqueue_active` / `clientqueue_queue_depth` | gauge | running / waiting now |
+| `clientqueue_waiting_clients` | gauge | clients with at least one request waiting (`queue_depth` counts requests, this counts clients) |
 | `clientqueue_clients` | gauge | clients currently tracked |
 
 A **burst** is one client's busy period: the peak number of its requests running plus waiting between

pkg/middleware/clientqueue.go

@@ -70,6 +70,16 @@ var (
 		Help: "Requests currently waiting for a slot",
 	})
 
+	queueEnqueued = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "clientqueue_enqueued_total",
+		Help: "Requests ever placed in a wait queue, whatever their outcome (ran, timed out or cancelled)",
+	})
+
+	queueWaitingClients = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "clientqueue_waiting_clients",
+		Help: "Clients currently with at least one request waiting for a slot",
+	})
+
 	queueClients = promauto.NewGauge(prometheus.GaugeOpts{
 		Name: "clientqueue_clients",
 		Help: "Clients currently tracked by the queue",
@@ -275,9 +285,13 @@ func (q *ClientQueue) acquire(ctx context.Context, key string) error {
 	}
 	w := &queueWaiter{ready: make(chan struct{})}
 	w.elem = c.waiters.PushBack(w)
+	if c.waiters.Len() == 1 {
+		queueWaitingClients.Inc()
+	}
 	c.enter()
 	q.mu.Unlock()
 	queueDepth.Inc()
+	queueEnqueued.Inc()
 
 	timer := time.NewTimer(q.cfg.MaxWait)
 	defer timer.Stop()
@@ -302,6 +316,9 @@ func (q *ClientQueue) acquire(ctx context.Context, key string) error {
 		q.releaseLocked(key)
 	} else {
 		c.waiters.Remove(w.elem)
+		if c.waiters.Len() == 0 {
+			queueWaitingClients.Dec()
+		}
 		c.leave()
 		queueDepth.Dec()
 	}
@@ -331,6 +348,9 @@ func (q *ClientQueue) releaseLocked(key string) {
 	queueActive.Dec()
 	if front := c.waiters.Front(); front != nil {
 		w := c.waiters.Remove(front).(*queueWaiter)
+		if c.waiters.Len() == 0 {
+			queueWaitingClients.Dec()
+		}
 		w.granted = true
 		queueDepth.Dec()
 		queueActive.Inc()

pkg/middleware/clientqueue_test.go

@@ -2,6 +2,7 @@ package middleware
 
 import (
 	"context"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -278,6 +279,7 @@ func TestClientQueueMetrics(t *testing.T) {
 	q := newTestQueue(t, ClientQueueConfig{MaxConcurrent: 2})
 	imm0 := gaugeVal(t, queueRequests.WithLabelValues("immediate"))
 	que0 := gaugeVal(t, queueRequests.WithLabelValues("queued"))
+	enq0 := gaugeVal(t, queueEnqueued)
 	bc0, bs0 := histVal(t, queueBurst)
 	wc0, _ := histVal(t, queueWait)
 
@@ -317,6 +319,9 @@ func TestClientQueueMetrics(t *testing.T) {
 	if got := gaugeVal(t, queueRequests.WithLabelValues("immediate")) - imm0; got != 2 {
 		t.Errorf("immediate = %v, want 2", got)
 	}
+	if got := gaugeVal(t, queueEnqueued) - enq0; got != 3 {
+		t.Errorf("enqueued = %v, want 3", got)
+	}
 	if got := gaugeVal(t, queueRequests.WithLabelValues("queued")) - que0; got != 3 {
 		t.Errorf("queued = %v, want 3", got)
 	}
@@ -331,3 +336,99 @@ func TestClientQueueMetrics(t *testing.T) {
 		t.Errorf("burst max = %v, want >= 5", got)
 	}
 }
+
+func TestClientQueueWaitingClientsGauge(t *testing.T) {
+	q := newTestQueue(t, ClientQueueConfig{MaxConcurrent: 1, MaxWait: 100 * time.Millisecond})
+	base := gaugeVal(t, queueWaitingClients)
+	waiting := func() float64 { return gaugeVal(t, queueWaitingClients) - base }
+	waitFor := func(want float64) {
+		t.Helper()
+		deadline := time.Now().Add(2 * time.Second)
+		for waiting() != want {
+			if time.Now().After(deadline) {
+				t.Fatalf("waiting clients = %v, want %v", waiting(), want)
+			}
+			time.Sleep(time.Millisecond)
+		}
+	}
+
+	// Two clients each hold their only slot.
+	for _, k := range []string{"a", "b"} {
+		if err := q.acquire(t.Context(), k); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if waiting() != 0 {
+		t.Fatalf("waiting = %v with nobody queued", waiting())
+	}
+
+	// Two waiters for "a" count as one waiting client, not two.
+	bg := func(ctx context.Context, k string) chan error {
+		ch := make(chan error, 1)
+		go func() { ch <- q.acquire(ctx, k) }()
+		return ch
+	}
+	a1 := bg(t.Context(), "a")
+	waitFor(1)
+	a2 := bg(t.Context(), "a")
+	time.Sleep(10 * time.Millisecond)
+	waitFor(1)
+
+	// A waiter for "b" adds a second waiting client, and cancelling it drops it.
+	cctx, cancel := context.WithCancel(t.Context())
+	b1 := bg(cctx, "b")
+	waitFor(2)
+	cancel()
+	if err := <-b1; err == nil {
+		t.Fatal("expected cancellation")
+	}
+	waitFor(1)
+
+	// Draining "a": the first release hands over to a1 (one still waits),
+	// the second hands over to a2 and "a" stops waiting.
+	q.release("a")
+	if err := <-a1; err != nil {
+		t.Fatal(err)
+	}
+	waitFor(1)
+	q.release("a")
+	if err := <-a2; err != nil {
+		t.Fatal(err)
+	}
+	waitFor(0)
+	q.release("a")
+	q.release("a")
+
+	// Timeout: "b" still holds its slot, so a new waiter times out.
+	b2 := bg(t.Context(), "b")
+	waitFor(1)
+	if err := <-b2; !errors.Is(err, errQueueWait) {
+		t.Fatalf("err = %v, want timeout", err)
+	}
+	waitFor(0)
+	q.release("b")
+}
+
+func TestClientQueueEnqueuedCountsAllOutcomes(t *testing.T) {
+	q := newTestQueue(t, ClientQueueConfig{MaxConcurrent: 1, MaxQueue: 1, MaxWait: 50 * time.Millisecond})
+	base := gaugeVal(t, queueEnqueued)
+	if err := q.acquire(t.Context(), "k"); err != nil { // immediate: not enqueued
+		t.Fatal(err)
+	}
+	if err := q.acquire(t.Context(), "k"); !errors.Is(err, errQueueWait) { // enqueued, times out
+		t.Fatalf("err = %v, want timeout", err)
+	}
+	cctx, cancel := context.WithCancel(t.Context())
+	done := make(chan error, 1)
+	go func() { done <- q.acquire(cctx, "k") }() // enqueued, cancelled
+	time.Sleep(10 * time.Millisecond)
+	if err := q.acquire(t.Context(), "k"); !errors.Is(err, errQueueFull) { // rejected: not enqueued
+		t.Fatalf("err = %v, want queue full", err)
+	}
+	cancel()
+	<-done
+	q.release("k")
+	if got := gaugeVal(t, queueEnqueued) - base; got != 2 {
+		t.Fatalf("enqueued = %v, want 2 (timeout + cancel; not immediate or rejected)", got)
+	}
+}

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)
@@ -840,26 +851,34 @@ 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
+	var updates map[string]interface{}
+	if m, ok := hookCtx.Data.(map[string]interface{}); ok {
+		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 {
-	if err := json.Unmarshal(dataBytes, hookCtx.ModelPtr); err != nil {
+			return nil, fmt.Errorf("failed to unmarshal data into map: %w", err)
-		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)
+
+	// Only the keys present in the request are written. "" and null overwrite
+	// 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
 	return h.readByID(hookCtx)

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)
@@ -709,26 +720,34 @@ 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
+	var updates map[string]interface{}
+	if m, ok := hookCtx.Data.(map[string]interface{}); ok {
+		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 {
-	if err := json.Unmarshal(dataBytes, hookCtx.ModelPtr); err != nil {
+			return nil, fmt.Errorf("failed to unmarshal data into map: %w", err)
-		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)
+
+	// Only the keys present in the request are written. "" and null overwrite
+	// 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
 	return h.readByID(hookCtx)