fix(delegate): avoid merging into object of Decimal, Date, etc.

packages/runtime/package.json

@@ -83,6 +83,7 @@
         "decimal.js": "^10.4.2",
         "deepcopy": "^2.1.0",
         "deepmerge": "^4.3.1",
+        "is-plain-object": "^5.0.0",
         "logic-solver": "^2.0.1",
         "lower-case-first": "^2.0.2",
         "pluralize": "^8.0.0",

packages/runtime/src/enhancements/delegate.ts

@@ -1,6 +1,7 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 import deepcopy from 'deepcopy';
 import deepmerge, { type ArrayMergeOptions } from 'deepmerge';
+import { isPlainObject } from 'is-plain-object';
 import { lowerCaseFirst } from 'lower-case-first';
 import { DELEGATE_AUX_RELATION_PREFIX } from '../constants';
 import {
@@ -1094,6 +1095,7 @@ export class DelegateProxyHandler extends DefaultPrismaProxyHandler {
 
         const result = deepmerge(upMerged, downMerged, {
             arrayMerge: combineMerge,
+            isMergeableObject: (v) => isPlainObject(v) || Array.isArray(v), // avoid messing with Decimal, Date, etc.
         });
         return result;
     }

tests/regression/tests/issue-1487.test.ts

@@ -0,0 +1,71 @@
+import { createPostgresDb, dropPostgresDb, loadSchema } from '@zenstackhq/testtools';
+import Decimal from 'decimal.js';
+
+describe('issue 1487', () => {
+    it('regression2', async () => {
+        const dbUrl = await createPostgresDb('issue-1487');
+        let prisma: any;
+
+        try {
+            const r = await loadSchema(
+                `
+                model LineItem {
+                    id Int @id @default(autoincrement())
+                    price Decimal
+                    createdAt DateTime @default(now())
+
+                    orderId Int
+                    order Order @relation(fields: [orderId], references: [id])
+                }
+                model Order extends BaseType {
+                    total Decimal
+                    createdAt DateTime @default(now())
+                    lineItems LineItem[]
+                }
+                model BaseType {
+                    id Int @id @default(autoincrement())
+                    entityType String
+
+                    @@delegate(entityType)
+                }
+                `,
+                {
+                    provider: 'postgresql',
+                    dbUrl,
+                    enhancements: ['omit', 'delegate'],
+                }
+            );
+
+            prisma = r.prisma;
+            const db = r.enhance();
+
+            const create = await db.Order.create({
+                data: {
+                    total: new Decimal(100_100.99),
+                    lineItems: { create: [{ price: 90_000.66 }, { price: 20_100.33 }] },
+                },
+            });
+
+            const order = await db.Order.findFirst({ where: { id: create.id }, include: { lineItems: true } });
+            expect(Decimal.isDecimal(order.total)).toBe(true);
+            expect(order.createdAt instanceof Date).toBe(true);
+            expect(order.total.toString()).toEqual('100100.99');
+            order.lineItems.forEach((item: any) => {
+                expect(Decimal.isDecimal(item.price)).toBe(true);
+                expect(item.price.toString()).not.toEqual('[object Object]');
+            });
+
+            const lineItems = await db.LineItem.findMany();
+            lineItems.forEach((item: any) => {
+                expect(item.createdAt instanceof Date).toBe(true);
+                expect(Decimal.isDecimal(item.price)).toBe(true);
+                expect(item.price.toString()).not.toEqual('[object Object]');
+            });
+        } finally {
+            if (prisma) {
+                await prisma.$disconnect();
+            }
+            await dropPostgresDb('issue-1487');
+        }
+    });
+});