Add EF Core, Npgsql, Todo entity, and AppDbContext

backend/Data/AppDbContext.cs

@@ -0,0 +1,25 @@
+using Backend.Models;
+using Microsoft.EntityFrameworkCore;
+
+namespace Backend.Data;
+
+public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
+{
+    public DbSet<Todo> Todos => Set<Todo>();
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.Entity<Todo>(e =>
+        {
+            e.ToTable("todos", schema: "public");
+            e.HasKey(x => x.Id);
+            e.Property(x => x.Id).HasColumnName("id").ValueGeneratedOnAdd();
+            e.Property(x => x.UserId).HasColumnName("user_id").IsRequired();
+            e.Property(x => x.Title).HasColumnName("title").IsRequired().HasMaxLength(500);
+            e.Property(x => x.Completed).HasColumnName("completed").IsRequired();
+            e.Property(x => x.CreatedAt).HasColumnName("created_at").IsRequired();
+            e.HasIndex(x => new { x.UserId, x.CreatedAt })
+                .HasDatabaseName("todos_user_id_created_at_idx");
+        });
+    }
+}