[FA-misc] Initial MassTransit implementation seems to work

FictionArchive.Service.UserNovelDataService/Consumers/NovelCreatedConsumer.cs

@@ -0,0 +1,39 @@
+using FictionArchive.Service.Shared.Contracts.Events;
+using FictionArchive.Service.UserNovelDataService.Models.Database;
+using FictionArchive.Service.UserNovelDataService.Services;
+using MassTransit;
+using Microsoft.EntityFrameworkCore;
+
+namespace FictionArchive.Service.UserNovelDataService.Consumers;
+
+public class NovelCreatedConsumer : IConsumer<INovelCreated>
+{
+    private readonly ILogger<NovelCreatedConsumer> _logger;
+    private readonly UserNovelDataServiceDbContext _dbContext;
+
+    public NovelCreatedConsumer(
+        ILogger<NovelCreatedConsumer> logger,
+        UserNovelDataServiceDbContext dbContext)
+    {
+        _logger = logger;
+        _dbContext = dbContext;
+    }
+
+    public async Task Consume(ConsumeContext<INovelCreated> context)
+    {
+        var message = context.Message;
+
+        var exists = await _dbContext.Novels.AnyAsync(n => n.Id == message.NovelId);
+        if (exists)
+        {
+            _logger.LogDebug("Novel {NovelId} already exists, skipping", message.NovelId);
+            return;
+        }
+
+        var novel = new Novel { Id = message.NovelId };
+        _dbContext.Novels.Add(novel);
+        await _dbContext.SaveChangesAsync();
+
+        _logger.LogInformation("Created novel stub for {NovelId}", message.NovelId);
+    }
+}