Converted the project in C#, added Entity Framework Core.

DbManager.cs

@@ -0,0 +1,21 @@
+using Microsoft.EntityFrameworkCore;
+using System;
+using System.Collections.Generic;
+
+namespace IsleBot;
+
+public class DbManager : DbContext {
+    public DbSet<User> Players { get; set; }
+    public DbSet<Card> Cards { get; set; }
+    public DbSet<Match> Matches { get; set; }
+
+    public string dbpath { get; } = "database.db";
+
+    public DbManager() {
+        var fullPath = Environment.CurrentDirectory + Path.DirectorySeparatorChar + dbpath;
+        dbpath = fullPath;
+    }
+
+    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) 
+        => optionsBuilder.UseSqlite($"Data Source={dbpath}");
+}