Added comb guid generation for sql server ids.

src/Core/Repositories/SqlServer/Repository.cs

@@ -10,6 +10,8 @@ namespace Bit.Core.Repositories.SqlServer
 {
     public abstract class Repository<T, TModel> : IRepository<T> where T : IDataObject where TModel : ITableModel<T>
     {
+        private static readonly long _baseDateTicks = new DateTime(1900, 1, 1).Ticks;
+
         public Repository(string connectionString, string schema = null, string table = null)
         {
             if(string.IsNullOrWhiteSpace(connectionString))
@@ -55,7 +57,7 @@ namespace Bit.Core.Repositories.SqlServer
 
         public virtual async Task CreateAsync(T obj)
         {
-            obj.Id = Guid.NewGuid().ToString();
+            obj.Id = GenerateComb().ToString();
             var tableModel = (TModel)Activator.CreateInstance(typeof(TModel), obj);
 
             using(var connection = new SqlConnection(ConnectionString))
@@ -107,5 +109,36 @@ namespace Bit.Core.Repositories.SqlServer
                     commandType: CommandType.StoredProcedure);
             }
         }
+
+        /// <summary>
+        /// Generate sequential Guid for Sql Server.
+        /// ref: https://github.com/nhibernate/nhibernate-core/blob/master/src/NHibernate/Id/GuidCombGenerator.cs
+        /// </summary>
+        /// <returns>A comb Guid.</returns>
+        protected Guid GenerateComb()
+        {
+            byte[] guidArray = Guid.NewGuid().ToByteArray();
+
+            var now = DateTime.UtcNow;
+
+            // Get the days and milliseconds which will be used to build the byte string 
+            var days = new TimeSpan(now.Ticks - _baseDateTicks);
+            var msecs = now.TimeOfDay;
+
+            // Convert to a byte array 
+            // Note that SQL Server is accurate to 1/300th of a millisecond so we divide by 3.333333 
+            var daysArray = BitConverter.GetBytes(days.Days);
+            var msecsArray = BitConverter.GetBytes((long)(msecs.TotalMilliseconds / 3.333333));
+
+            // Reverse the bytes to match SQL Servers ordering 
+            Array.Reverse(daysArray);
+            Array.Reverse(msecsArray);
+
+            // Copy the bytes into the guid 
+            Array.Copy(daysArray, daysArray.Length - 2, guidArray, guidArray.Length - 6, 2);
+            Array.Copy(msecsArray, msecsArray.Length - 4, guidArray, guidArray.Length - 4, 4);
+
+            return new Guid(guidArray);
+        }
     }
 }