Database migration, repository, controller and service

Services/DocumentService.cs

@@ -0,0 +1,22 @@
+using PaperlessAI.Models;
+using PaperlessAI.Repositories;
+
+namespace PaperlessAI.Services;
+
+public class PaperlessDocumentService(PaperlessDocumentRepository docRepo)
+{
+    public async Task<bool> Exists(long documentId)
+    {
+        if(documentId < 0 || documentId > long.MaxValue)
+            throw new Exception($"Value \"{documentId}\" must be in Range between 0 - {long.MaxValue}!");
+        
+        return await docRepo.Get(documentId) != null;
+    }
+
+    public async Task<PaperlessDocument> Create(long documentId)
+    {
+        var doc = PaperlessDocument.Create(documentId);
+        await docRepo.Add(doc);
+        return doc;
+    }
+}