Add .NET Core 2.1 versions

worker/dotnet/Worker/Data/IVoteData.cs

@@ -0,0 +1,7 @@
+namespace Worker.Data
+{
+    public interface IVoteData
+    {
+        void Set(string voterId, string vote);
+    }
+}

worker/dotnet/Worker/Data/MySqlVoteData.cs

@@ -0,0 +1,35 @@
+using Microsoft.Extensions.Logging;
+using Worker.Entities;
+
+namespace Worker.Data
+{
+    public class MySqlVoteData : IVoteData
+    {
+        private readonly VoteContext _context;        
+        private readonly ILogger _logger;
+
+        public MySqlVoteData(VoteContext context, ILogger<MySqlVoteData> logger)
+        {
+            _context = context;
+            _logger = logger;            
+        }
+
+        public void Set(string voterId, string vote)
+        {
+            var currentVote = _context.Votes.Find(voterId);
+            if (currentVote == null)
+            {
+                _context.Votes.Add(new Vote
+                {
+                    VoterId = voterId,
+                    VoteOption = vote
+                });
+            }
+            else if (currentVote.VoteOption != vote)
+            {
+                currentVote.VoteOption = vote;
+            }
+            _context.SaveChanges();
+        }
+    }
+}