feat: add AssetItem.purchaseOrderId (nullable FK)

prisma/schema.prisma

@@ -78,11 +78,16 @@ enum AssetItemStatus {
 
 // Hardware inventory — see docs/asset-license-management.md's "Data model
 // (sơ bộ)" table (serial number, model, ngày mua, bảo hành, trạng thái).
-// No Vendor/Assignment relation yet — those entities don't exist yet
-// (see "Việc còn dở" in CLAUDE.md), so this is a standalone entity for now,
-// same starting shape as Employee before Request grew an FK to it.
-// warrantyEndDate is nullable: not every asset has known warranty terms at
-// intake time (smallest sensible assumption — doesn't block creation).
+// No Assignment relation yet — that entity doesn't exist yet (see "Việc còn
+// dở" in CLAUDE.md). warrantyEndDate is nullable: not every asset has known
+// warranty terms at intake time (smallest sensible assumption — doesn't
+// block creation). purchaseOrderId is a nullable FK to PurchaseOrder — see
+// docs/asset-license-management.md's "## PurchaseOrder (gộp Receipt)"
+// Traceability bullet: supply-side traceability ("which PO did this asset
+// item come in through"). Nullable because not every AssetItem goes through
+// a formal PO (e.g. historical stock predating the system). Set at
+// intake/creation time only — no update endpoint for this field yet, same
+// precedent as License.vendorId being set-at-creation with no PATCH.
 model AssetItem {
   id              String          @id @default(uuid()) @db.Uuid
   serialNumber    String          @unique @map("serial_number")
@@ -90,6 +95,8 @@ model AssetItem {
   purchaseDate    DateTime        @map("purchase_date") @db.Date
   warrantyEndDate DateTime?       @map("warranty_end_date") @db.Date
   status          AssetItemStatus @default(in_stock)
+  purchaseOrderId String?         @map("purchase_order_id") @db.Uuid
+  purchaseOrder   PurchaseOrder?  @relation(fields: [purchaseOrderId], references: [id])
   createdAt       DateTime        @default(now()) @map("created_at") @db.Timestamptz(6)
 
   @@map("asset_items")
@@ -167,18 +174,20 @@ model Vendor {
 // received) — enforced at the Zod layer (src/lib/purchase-orders.ts), not a
 // DB constraint, same approach as other cross-field invariants in this
 // codebase (e.g. Assignment's assetItemId/licenseId XOR, not built yet).
-// purchaseOrderId back-references on AssetItem/License/Request (traceability,
-// same doc section) are NOT part of this change — out of scope for this task.
+// `assetItems` is the back-relation from the AssetItem.purchaseOrderId
+// retrofit (supply-side traceability, same doc section). License/Request
+// back-references are NOT part of this change — out of scope for this task.
 model PurchaseOrder {
-  id           String    @id @default(uuid()) @db.Uuid
-  vendorId     String    @map("vendor_id") @db.Uuid
-  vendor       Vendor    @relation(fields: [vendorId], references: [id])
-  orderDate    DateTime  @map("order_date") @db.Timestamptz(6)
-  expectedDate DateTime  @map("expected_date") @db.Timestamptz(6)
-  receivedAt   DateTime? @map("received_at") @db.Timestamptz(6)
-  receivedById String?   @map("received_by") @db.Uuid
-  receivedBy   Employee? @relation(fields: [receivedById], references: [id])
-  createdAt    DateTime  @default(now()) @map("created_at") @db.Timestamptz(6)
+  id           String      @id @default(uuid()) @db.Uuid
+  vendorId     String      @map("vendor_id") @db.Uuid
+  vendor       Vendor      @relation(fields: [vendorId], references: [id])
+  orderDate    DateTime    @map("order_date") @db.Timestamptz(6)
+  expectedDate DateTime    @map("expected_date") @db.Timestamptz(6)
+  receivedAt   DateTime?   @map("received_at") @db.Timestamptz(6)
+  receivedById String?     @map("received_by") @db.Uuid
+  receivedBy   Employee?   @relation(fields: [receivedById], references: [id])
+  createdAt    DateTime    @default(now()) @map("created_at") @db.Timestamptz(6)
+  assetItems   AssetItem[]
 
   @@map("purchase_orders")
 }