Tasks Module and Service Architecture Controllers, services, dependency injection, and a clean Prisma boundary
Phase 11 - Persistent Task CRUD API Volume 03 - Database Engineering
Architecture milestone HTTP routing
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Phase 11 replaces process memory with durable PostgreSQL-backed application behavior.
The module we actually need The old TodosModule stored data in memory. Phase 11 introduces TasksModule because Task is now the durable domain resource. We do not create repository abstractions yet; PrismaService already gives the service a clean database dependency.
src/tasks/ tasks.module.ts tasks.controller.ts tasks.service.ts tasks.types.ts
Module wiring
import { Module } from "@nestjs/common";
import { TasksController } from "./tasks.controller";
import { TasksService } from "./tasks.service";@Module({
controllers: [TasksController],
providers: [TasksService],
})
export class TasksModule {}PrismaModule is global from Phase 09, so TasksModule does not need to import it explicitly. TasksService can request PrismaService through Nest dependency injection.
Application module
import { Module } from "@nestjs/common";
import { ConfigModule } from "@nestjs/config";
import { HealthModule } from "./health/health.module";
import { PrismaModule } from "./prisma/prisma.module";
import { TasksModule } from "./tasks/tasks.module";@Module({ imports: [ ConfigModule.forRoot({ isGlobal: true }), PrismaModule, HealthModule, TasksModule, ], }) export class AppModule {}
Why remove TodosModule from AppModule?
The old /todos endpoint represented temporary storage. Leaving it registered beside /tasks would create two competing resource models and confuse the learning architecture.
import { TaskPriority, TaskStatus, } from "../generated/prisma/client";
// These are compile-time shapes only. Phase 12 replaces this temporary // boundary with DTOs + runtime validation. export type CreateTaskInput = { projectId: string; title: string; description?: string | null; };
export type UpdateTaskInput = { title?: string; description?: string | null; status?: TaskStatus; priority?: TaskPriority; };
These TypeScript types help the editor and compiler, but they do not validate JSON received from the network. A caller can still send an invalid string at runtime. Phase 12 replaces this temporary boundary with DTOs and runtime validation.
Service dependency graph Figure 1 - Nest dependency graph TasksController
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Nest wires class dependencies; Prisma handles persistence; the database remains the final integrity boundary.
Controller vs service Controller owns Service owns
NestJS guidance consistently treats controllers as request handlers that delegate more complex work to injectable providers/services. That separation is the pattern TaskFlow follows here.
Tasks Module and Service Architecture matters because it changes a real boundary in TaskFlow. The goal is to understand the inputs, owner, observable output, and failure modes before adding more abstraction.
Restate the goal of “Tasks Module and Service Architecture” as one observable behavior. Write the success signal before touching code.
Trace the boundary map: request → validated command → invariant → state transition → persisted result. Mark the one boundary this lesson changes.
Inspect the current repository state and record the exact files, route, table, or runtime involved. Avoid creating an abstraction before you can name the existing owner.
Implement the smallest vertical slice. Add one coherent change, run the narrowest verification command, and read the output before continuing.
Connect the slice to TaskFlow’s phase artifact: Working /tasks API supporting create/list/read/update/delete against PostgreSQL with consistent error behavior.. Verify behavior from the outside as a user or API client would.
Create one controlled failure that is safe to reproduce. Predict the symptom first, capture evidence, locate the earliest broken boundary, then fix only that cause.
Close the reference and rebuild or explain the core change from memory. Record what you would monitor or test before trusting the same change in production.
if (task.status === "DONE") {
throw new TaskAlreadyCompletedError(task.id);
}
task.status = "DONE";
task.completedAt = new Date();Do not copy this as a finished answer. Predict what each boundary does, type the smallest useful slice, run it, then compare the result with your prediction.
Return to the nearest observable boundary: input, network, process log, database, or rendered UI. Compare actual evidence with the predicted path.
Change one variable at a time and reproduce the original failure after the fix; otherwise you have correlation, not diagnosis.
Without copying the final source, create a second small scenario that applies “Tasks Module and Service Architecture” to a different TaskFlow resource or input. Write the acceptance criteria first, implement it, and provide the evidence that each criterion is satisfied.
Implement list/read with deterministic ordering and missing-record behavior.
Use the smallest change that demonstrates this lesson. Stop after it works and capture evidence.Missing records bubble up as raw ORM exceptions
Predict the symptom before causing the failure. Then locate the earliest boundary where reality diverges from expectation.Why does this responsibility live here, what input does it trust, what output proves success, and what would go wrong if another layer owned it?
If your explanation is vague, repeat the boundary trace before moving on.Close the reference. Reproduce the core idea from memory or explain the exact request/data flow aloud. Then check your diff or notes for accidental shortcuts that bypass validation, authorization, error handling, or verification earned in earlier phases.