feat(categories): implement category management with hierarchical structure and update product association

backend/src/categories/categories.controller.ts

@@ -0,0 +1,20 @@
+import { Controller, Get } from '@nestjs/common';
+import { CategoriesService } from './categories.service';
+import { Public } from '../auth/decorators/public.decorator';
+
+@Controller('api/categories')
+export class CategoriesController {
+  constructor(private readonly categoriesService: CategoriesService) {}
+
+  @Public()
+  @Get()
+  findAll() {
+    return this.categoriesService.findAll();
+  }
+
+  @Public()
+  @Get('tree')
+  findTree() {
+    return this.categoriesService.findTree();
+  }
+}

backend/src/categories/categories.module.ts

@@ -0,0 +1,12 @@
+import { Module } from '@nestjs/common';
+import { CategoriesService } from './categories.service';
+import { CategoriesController } from './categories.controller';
+import { PrismaModule } from '../prisma/prisma.module';
+
+@Module({
+  imports: [PrismaModule],
+  providers: [CategoriesService],
+  controllers: [CategoriesController],
+  exports: [CategoriesService],
+})
+export class CategoriesModule {}

backend/src/categories/categories.service.ts

@@ -0,0 +1,33 @@
+import { Injectable } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+
+export type CategoryNode = {
+  id: number;
+  name: string;
+  parentId: number | null;
+  children: CategoryNode[];
+};
+
+@Injectable()
+export class CategoriesService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async findAll() {
+    return this.prisma.category.findMany({ orderBy: { name: 'asc' } });
+  }
+
+  async findTree(): Promise<CategoryNode[]> {
+    const all = await this.prisma.category.findMany({ orderBy: { name: 'asc' } });
+    const map = new Map<number, CategoryNode>();
+    all.forEach((c) => map.set(c.id, { ...c, children: [] }));
+    const roots: CategoryNode[] = [];
+    map.forEach((node) => {
+      if (node.parentId === null) {
+        roots.push(node);
+      } else {
+        map.get(node.parentId)?.children.push(node);
+      }
+    });
+    return roots;
+  }
+}