First commit that builds.

code/MessengerBroker.Db/Model/Contracts/IForeignEntity.cs

@@ -0,0 +1,15 @@
+namespace MessengerBroker.Db.Model.Contracts
+{
+    public interface IForeignEntity
+    {
+        Guid Id { get; }
+
+        Guid BrokerId { get; }
+
+        bool IsDeleted { get; }
+
+        Sync? FirstSync { get; }
+
+        Sync? LastSync { get; }
+    }
+}

code/MessengerBroker.Db/Model/Message.cs

@@ -0,0 +1,9 @@
+namespace MessengerBroker.Db.Model
+{
+    public class Message
+    {
+        public Guid Id { get; set; }
+
+        public Guid BrokerId { get; set; }
+    }
+}

code/MessengerBroker.Db/Model/Sync.cs

@@ -0,0 +1,15 @@
+namespace MessengerBroker.Db.Model
+{
+    public class Sync
+    {
+        public int Id { get; set; }
+
+        public Guid BrokerId { get; set; }
+
+        public DateTime StartedUtc { get; set; }
+
+        public DateTime? FinishedUtc { get; set; }
+
+        public long? Changes { get; set; }
+    }
+}

code/MessengerBroker.Db/Model/User.cs

@@ -0,0 +1,11 @@
+using MessengerBroker.Db.Model.Contracts;
+
+namespace MessengerBroker.Db.Model
+{
+    public class User
+    {
+        public Guid Id { get; set; }
+
+        public Guid BrokerId { get; set; }
+    }
+}