fix(objectql): apply defaultValue on explicit null at insert (#2706)

Author: baozhoutao

.changeset/objectql-default-explicit-null.md

@@ -0,0 +1,13 @@
+---
+"@objectstack/objectql": patch
+---
+
+fix(objectql): apply field `defaultValue` when a field is explicitly `null` on insert, not only when omitted (#2706)
+
+`applyFieldDefaults` previously skipped any field whose value was not
+`undefined`, so a form that serialized an unpicked control as `null` (rather
+than omitting it) fell through and stored `null` — the `current_user` token and
+static defaults never filled in. Both an omitted field and an explicit `null`
+now count as "no value supplied" and receive the default. This runs on the
+insert path only, so a deliberate "set to null" on update is untouched; an
+explicit empty string `''` is still respected as a real value.

packages/objectql/src/engine.test.ts

@@ -319,6 +319,50 @@ describe('ObjectQL Engine', () => {
             expect(arg.owner).toBeUndefined();
         });
 
+        it('backfills a default when the field is EXPLICITLY null, not just omitted (#2706)', async () => {
+            vi.mocked(SchemaRegistry.getObject).mockImplementation((name) => {
+                if (name === 'ticket') return {
+                    name: 'ticket',
+                    fields: {
+                        title: { type: 'text' },
+                        owner: { type: 'user', reference: 'sys_user', defaultValue: 'current_user' },
+                        status: { type: 'text', defaultValue: 'planned' },
+                    },
+                } as any;
+                if (name === 'sys_user') return { name: 'sys_user', fields: { name: { type: 'text' } } } as any;
+                return undefined;
+            });
+
+            // A form serializes an unpicked control as explicit `null` (not
+            // omission) — both the dynamic `current_user` token and a static
+            // default must still fill in.
+            await engine.insert('ticket', { title: 'T1', owner: null, status: null }, { context: { userId: 'u-42' } as any });
+
+            expect(mockDriver.create).toHaveBeenCalledWith(
+                'ticket',
+                expect.objectContaining({ title: 'T1', owner: 'u-42', status: 'planned' }),
+                expect.anything(),
+            );
+        });
+
+        it('respects an explicit empty-string value and does not overwrite it with the default (#2706)', async () => {
+            vi.mocked(SchemaRegistry.getObject).mockImplementation((name) => {
+                if (name === 'ticket') return {
+                    name: 'ticket',
+                    fields: {
+                        title: { type: 'text' },
+                        status: { type: 'text', defaultValue: 'planned' },
+                    },
+                } as any;
+                return undefined;
+            });
+
+            await engine.insert('ticket', { title: 'T1', status: '' });
+
+            const arg = (mockDriver.create as any).mock.calls.at(-1)[1];
+            expect(arg.status).toBe('');
+        });
+
         it('resolves field defaults BEFORE beforeInsert so a hook can derive from them (#2703)', async () => {
             vi.mocked(SchemaRegistry.getObject).mockImplementation((name) => {
                 if (name === 'ticket') return {

packages/objectql/src/engine.ts

@@ -779,6 +779,14 @@ export class ObjectQL implements IDataEngine {
    * defaults are applied verbatim. Records that already supplied a value for a
    * field are left untouched.
    *
+   * "Supplied a value" means the field is present with a non-null value. Both an
+   * OMITTED field (`undefined`) and an EXPLICIT `null` are treated as "not
+   * supplied" and get the default. This runs on the INSERT path only, where a
+   * `null` from a form (an unpicked control serializes to `null`, not omission)
+   * unambiguously means "no value"; the UPDATE path never calls this, so a
+   * deliberate "set to null" on update is preserved (#2706). Empty string `''`
+   * is a real, user-entered value and is left as-is.
+   *
    * Implements ROADMAP §M9.9b — `defaultValue` accepts Expression so authors
    * can replace "write a hook to default to today/current-user" with a
    * declarative `defaultValue: cel\`today()\``.
@@ -799,7 +807,11 @@ export class ObjectQL implements IDataEngine {
     const out = { ...record };
     const now = nowSnapshot ?? new Date();
     for (const f of fieldEntries) {
-      if (out[f.name] !== undefined) continue;
+      // Apply the default when the field is either OMITTED (`undefined`) or an
+      // EXPLICIT `null` — both mean "no value supplied" on insert (#2706). A
+      // real value (including `''`) is respected. Insert-only path, so an
+      // intentional "set to null" on update is never touched here.
+      if (out[f.name] != null) continue;
       if (f.defaultValue == null) continue;
       const dv = f.defaultValue;
       if (typeof dv === 'object' && dv !== null && (dv as any).dialect && typeof (dv as any).source === 'string') {