day2

Day 2 — Data Persistence, Validation & Error Handling

🎯 Learning Objectives

By the end of Day 2, you will be able to:

• Configure Entity Framework Core 10 with PostgreSQL
• Design entity relationships using Fluent API configuration
• Implement request validation using FluentValidation and built-in .NET 10 validation
• Return standardized error responses using RFC 9457 Problem Details

🌅 Morning Warm-Up

Quick review questions from Day 1:

1. What is the difference between Results.Ok() and TypedResults.Ok()?
2. How do route groups help organize a Minimal API?
3. What replaced Swashbuckle in .NET 10?
4. Name three HTTP status codes and when to use them.

📖 Topics

1. Entity Framework Core 10 — DbContext, Fluent API, relationships, migrations, LINQ queries, N+1 prevention, new EF Core 10 features (LeftJoin, JSON columns)
2. Validation — .NET 10 built-in validation, FluentValidation, endpoint filters, ValidationProblemDetails
3. Problem Details & Error Handling — RFC 9457, IExceptionHandler, global error handling strategies

🧪 Lab

Lab 2 — Persistence & Validation: Add PostgreSQL persistence with EF Core, implement FluentValidation rules, and handle errors with Problem Details.

Scaffold level: 60% (DbContext skeleton provided, write configurations and validation)

🔎 Reference Demo & Cheatsheet

• Day 2 Persistence, Validation & Error Handling Cheat Sheet — condensed notes for the essential day 2 topics with direct links into the companion code
• Day 2 demos — runnable SQLite and PostgreSQL reference APIs showing EF Core setup, migrations, validation filters, Problem Details, and .http requests

📚 Key Packages Introduced Today

Package	Purpose
Microsoft.EntityFrameworkCore	ORM framework
Npgsql.EntityFrameworkCore.PostgreSQL	PostgreSQL provider
Microsoft.EntityFrameworkCore.Design	Migration tooling
FluentValidation.DependencyInjectionExtensions	Validation with DI