Add project files.

BudgetApp/Data/ApplicationDbContext.cs

@@ -0,0 +1,59 @@
+using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore;
+
+namespace BudgetApp.Data;
+
+public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
+{
+    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
+        : base(options)
+    {
+    }
+
+    public DbSet<Account> Accounts => Set<Account>();
+    public DbSet<Transaction> Transactions => Set<Transaction>();
+    public DbSet<Category> Categories => Set<Category>();
+
+    protected override void OnModelCreating(ModelBuilder builder)
+    {
+        base.OnModelCreating(builder);
+
+        builder.Entity<Account>(e =>
+        {
+            e.HasOne(a => a.User)
+             .WithMany()
+             .HasForeignKey(a => a.UserId)
+             .OnDelete(DeleteBehavior.Cascade);
+
+            e.Property(a => a.CurrentBalance).HasColumnType("decimal(18,2)");
+        });
+
+        builder.Entity<Transaction>(e =>
+        {
+            e.HasOne(t => t.Account)
+             .WithMany(a => a.Transactions)
+             .HasForeignKey(t => t.AccountId)
+             .OnDelete(DeleteBehavior.Cascade);
+
+            e.HasOne(t => t.Category)
+             .WithMany(c => c.Transactions)
+             .HasForeignKey(t => t.CategoryId)
+             .OnDelete(DeleteBehavior.SetNull);
+
+            e.HasOne(t => t.ParentTransaction)
+             .WithMany()
+             .HasForeignKey(t => t.ParentTransactionId)
+             .OnDelete(DeleteBehavior.SetNull);
+
+            e.Property(t => t.Amount).HasColumnType("decimal(18,2)");
+        });
+
+        builder.Entity<Category>(e =>
+        {
+            e.HasOne(c => c.User)
+             .WithMany()
+             .HasForeignKey(c => c.UserId)
+             .OnDelete(DeleteBehavior.Cascade);
+        });
+    }
+}