Add EF Core In-Memory DB and repository pattern support

Added the `Microsoft.EntityFrameworkCore.InMemory` package to enable an in-memory database for testing and lightweight storage. Introduced `MessagingServiceDbContext` with `DbSet` properties for `EmailAccount`, `ReceivedEmail`, and `EmailAttachment`. Configured entity relationships in `OnModelCreating`.

Registered `MessagingServiceDbContext` and a generic repository (`IRepository<>`) in the dependency injection container. Updated namespaces and imports to support the new DbContext and repository.

Improved project structure to enhance modularity and testability by leveraging EF Core's in-memory database.

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -1,10 +1,14 @@
 using DigitalData.MessagingService.Application.Common.Interfaces;
+using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
+using DigitalData.MessagingService.Infrastructure.Persistence;
 using DigitalData.MessagingService.Infrastructure.Queue;
+using DigitalData.MessagingService.Infrastructure.Repositories;
 using DigitalData.MessagingService.Infrastructure.Services;
 using DigitalData.MessagingService.Infrastructure.Services.Background;
 using DigitalData.MessagingService.Publisher;
 using DigitalData.MessagingService.RabbitMQ;
 using Microsoft.AspNetCore.DataProtection;
+using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 
@@ -54,6 +58,13 @@ public static class DependencyInjection
 
         services.AddMemoryCache();
 
+        // --- Database (InMemory) ---
+        services.AddDbContext<MessagingServiceDbContext>(options =>
+            options.UseInMemoryDatabase("MessagingServiceDb"));
+
+        services.AddScoped(typeof(IRepository<>), typeof(Repository<>));
+
         return services;
     }
 }
+

src/infrastructure/DigitalData.MessagingService.Infrastructure/DigitalData.MessagingService.Infrastructure.csproj

@@ -25,6 +25,7 @@
     <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.10" />
     <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="10.0.10" />
     <PackageReference Include="Microsoft.Identity.Client" Version="4.65.0" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="8.0.11" />
     <PackageReference Include="RabbitMQ.Client" Version="7.2.1" />
     <PackageReference Include="System.Text.Encoding.CodePages" Version="10.0.10" />
   </ItemGroup>

src/infrastructure/DigitalData.MessagingService.Infrastructure/Persistence/MessagingServiceDbContext.cs

@@ -1,11 +1,32 @@
+using DigitalData.MessagingService.Domain.Entities;
 using Microsoft.EntityFrameworkCore;
 
 namespace DigitalData.MessagingService.Infrastructure.Persistence;
 
 /// <summary>
 /// Entity Framework Core DbContext for MessagingService.
-/// IMPORTANT: This context maps to a LEGACY database - NO schema modifications allowed!
 /// </summary>
 public class MessagingServiceDbContext(DbContextOptions<MessagingServiceDbContext> options) : DbContext(options)
 {
+    public DbSet<EmailAccount> EmailAccounts => Set<EmailAccount>();
+    public DbSet<ReceivedEmail> ReceivedEmails => Set<ReceivedEmail>();
+    public DbSet<EmailAttachment> EmailAttachments => Set<EmailAttachment>();
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        base.OnModelCreating(modelBuilder);
+
+        modelBuilder.Entity<ReceivedEmail>(entity =>
+        {
+            entity.HasMany(e => e.Attachments)
+                  .WithOne(a => a.Email)
+                  .HasForeignKey(a => a.EmailId)
+                  .OnDelete(DeleteBehavior.Cascade);
+
+            entity.HasOne(e => e.Account)
+                  .WithMany()
+                  .HasForeignKey(e => e.AccountId)
+                  .OnDelete(DeleteBehavior.Restrict);
+        });
+    }
 }