Your first ASP.NET App: Entity Framework

#webdev #csharp #aspnet #tutorial

Hello! In this tutorial we will build your own ASP.NET service with database and learn what is EF Core!

Requirements

IDE like Visual Studio/JetBrains Rider
.NET >= 10
Base C# skill
CPU (manually)

What is Entity Framework

EF Core is a tool for .NET developers that lets you work with databases using standard C# code without writing raw SQL queries. It automatically maps database tables into familiar C# classes and objects, handling all the heavy lifting behind the scenes. To fetch, modify, or save data, you simply write a few lines of C#, and EF Core translates them into the correct SQL commands. This speeds up development and protects you from typos and errors when interacting with a database.

Creating entity

First we need to create entity, is that object that will saving in database like postgres, sqlite, mssql, or oracle.

Create file with name MyData and paste this code

namespace ExampleProject;

public class MyData
{
    public Guid Id { get; set; }
    public required string Name { get; set; } 
    public required int Age { get; set; }
}

In this entity we have - Own Id, Name, Age

Creating DbContext

For work with EFC we need DbContext.

First we need to add EFC library -

dotnet add package Microsoft.EntityFrameworkCore
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.Sqlite

using Microsoft.EntityFrameworkCore;

namespace ExampleProject;

public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
{
    public DbSet<MyData> MyData  => Set<MyData>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<MyData>().Property(x => x.Id).ValueGeneratedOnAdd();
        modelBuilder.Entity<MyData>().HasKey(x => x.Id);
        modelBuilder.Entity<MyData>().Property(x => x.Name).IsRequired();
        modelBuilder.Entity<MyData>().Property(x => x.Age).IsRequired();
        base.OnModelCreating(modelBuilder);
    }
}

this code contains configuration for DB

Adding to DI

using ExampleProject;
using Microsoft.EntityFrameworkCore;
using Scalar.AspNetCore;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenApi();
builder.Services.AddControllers();

builder.Services.AddScoped<IMyService, MyService>();

builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlite("Data Source=app.db"));

var app = builder.Build();

if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    app.MapScalarApiReference();
}

app.MapControllers();

app.Run();

Updating our service

namespace ExampleProject;

public interface IMyService
{
    Task<string> GetHello(string name);
}

public class MyService(AppDbContext db) : IMyService
{
    public async Task<string> GetHello(string name)
    {
        await Task.Delay(150);
        await db.MyData.AddAsync(new MyData { Name = name, Age = 25 });
        await db.SaveChangesAsync();
        return $"Hello, {name}!";
    }
}

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