// courses table-এ services: ['live-session', 'pdf-notes'] // সমস্যা: // 1. Price কোথায় রাখব? // 2. Service কতজন কিনেছে? // 3. Admin কি service অফার করতে পারবে? // 4. Teacher নিজে service বাদ দিতে পারবে? // 5. Race condition — ২ জন একসাথে // update করলে?

-- 1. Master service list (Admin manage করে) CREATE TABLE AddOnService ( id UUID PRIMARY KEY, name VARCHAR(100), -- "Live Session" description TEXT, isActive BOOLEAN DEFAULT true ); -- 2. Course-এর default services (Teacher set করে) CREATE TABLE CourseDefaultService ( courseId UUID REFERENCES Course(id), serviceId UUID REFERENCES AddOnService(id), isEnabled BOOLEAN DEFAULT true, PRIMARY KEY (courseId, serviceId) ); -- 3. Admin force-add (overrides teacher) CREATE TABLE CourseAdminServiceOffering ( courseId UUID REFERENCES Course(id), serviceId UUID REFERENCES AddOnService(id), addedBy UUID REFERENCES User(id), PRIMARY KEY (courseId, serviceId) ); -- 4. Prices (per course per service) CREATE TABLE ServicePrice ( courseId UUID, serviceId UUID, price DECIMAL(10,2), currency VARCHAR(3) DEFAULT 'BDT', PRIMARY KEY (courseId, serviceId) ); -- 5. Student selection CREATE TABLE StudentServiceSelection ( studentId UUID REFERENCES User(id), courseId UUID, serviceId UUID, purchasedAt TIMESTAMP DEFAULT NOW(), PRIMARY KEY (studentId, courseId, serviceId) );

// ভুল — Race condition const exists = await prisma .courseDefaultService.findFirst({...}); if (!exists) { // রহিম ও হাচান দুজনেই এখানে আসল! await prisma.courseDefaultService.create({ data: { courseId, serviceId, isEnabled: true } }); // Duplicate key error! }

// সঠিক — Upsert (atomic) await prisma.courseDefaultService.upsert({ where: { courseId_serviceId: { courseId, serviceId } }, create: { courseId, serviceId, isEnabled: true }, update: { isEnabled: true } // রহিম ও হাচান একসাথে করলেও // PostgreSQL একটাই চালাবে // দুটো duplicate হবে না });

async function getTeacherServices( courseId: string, teacherId: string ) { // সব কিছু একবারে load const [defaults, adminAdded, prices] = await Promise.all([ // Teacher-এর default services prisma.courseDefaultService.findMany({ where: { courseId }, include: { service: true } }), // Admin force-added prisma.courseAdminServiceOffering.findMany({ where: { courseId }, include: { service: true } }), // সব prices prisma.servicePrice.findMany({ where: { courseId } }) ]); return formatTeacherServices( defaults, adminAdded, prices ); }

function formatTeacherServices( defaults, adminAdded, prices ) { // Price lookup map তৈরি (O(1) access) const priceMap = new Map( prices.map(p => [p.serviceId, p.price]) ); // Admin-added services set const adminSet = new Set( adminAdded.map(a => a.serviceId) ); // Smart merge const allServiceIds = new Set([ ...defaults.map(d => d.serviceId), ...adminAdded.map(a => a.serviceId) ]); return [...allServiceIds].map(serviceId => { const def = defaults.find( d => d.serviceId === serviceId ); const adm = adminAdded.find( a => a.serviceId === serviceId ); const service = def?.service || adm?.service; return { serviceId, name: service.name, isEnabled: adminSet.has(serviceId) ? true // Admin override — always on : (def?.isEnabled ?? false), isAdminForced: adminSet.has(serviceId), price: priceMap.get(serviceId) ?? 0, canDisable: !adminSet.has(serviceId), }; }); }