Entity framework 6.1 - Enable column ordering and where clause in an index

Configuration.cs

using System.Data.Entity.Migrations;


internal sealed class MyConfiguration : DbMigrationsConfiguration<MyContext>
{
    /// <summary>
    /// Constructor
    /// </summary>
    public MyConfiguration()
    {
        // Other stuff here...

        // Index/Unique custom generation (Ascending and Descending)
        SetSqlGenerator("System.Data.SqlClient", new CustomSqlServerMigrationSqlGenerator());
    }
}

CustomSqlServerMigrationSqlGenerator.cs

using System;
using System.Data.Entity.Migrations.Model;
using System.Data.Entity.SqlServer;
using System.Text;


/// <summary>
/// Entity framework custom code generator
/// 
/// Copyright 2019 - Maxime Jobin - All rights reserved
/// 
/// You can use and share this code as long as the copyright remains intact in your code.
/// </summary>
namespace S2B.APS.EntityFramework
{
	// Inspired by some code from Rowan Miller
	// http://romiller.com/2012/01/16/customizing-code-first-migrations-provider/
	public class CustomSqlServerMigrationSqlGenerator : SqlServerMigrationSqlGenerator
	{
		protected override void Generate(CreateIndexOperation createIndexOperation)
		{
			using (var writer = Writer())
			{
				var sql = new StringBuilder();

				sql.Append("CREATE ");

				if (createIndexOperation.IsUnique)
				{
					sql.Append("UNIQUE ");
				}

				if (createIndexOperation.IsClustered)
				{
					sql.Append("CLUSTERED ");
				}
				else
				{
					sql.Append("NONCLUSTERED ");
				}

				string name = createIndexOperation.Name;
				string[] sorts = {};
				string where = null;
				if (createIndexOperation.Name.Contains(":"))
				{
					var parts = createIndexOperation.Name.Split(':');
					
					if (parts.Length >= 1)
					{
						name = parts[0];
					}
					if (parts.Length >= 2)
					{
						sorts = parts[1].Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
					}
					if (parts.Length >= 3)
					{
						where = parts[2];
					}
				}

				sql.Append("INDEX ");
				sql.Append(Quote(name));
				sql.Append(" ON ");
				sql.Append(Name(createIndexOperation.Table));
				sql.Append("(");

				// Sort columns
				string fields = "";
				if (sorts.Length == 0 || sorts.Length == createIndexOperation.Columns.Count)
				{
					for (int i=0 ; i<createIndexOperation.Columns.Count ; i++)
					{
						string sort = "ASC";
						if (sorts.Length == 0)
						{
							// Nothing to do
						}
						else if (sorts[i] != "ASC" && sorts[i] != "DESC")
						{
							throw new Exception(string.Format("Expected sort for {0} is 'ASC' or 'DESC. Received: {1}", name, sorts[i]));
						}
						else 
						{ 
							sort = sorts[i];  
						}
						
						fields = fields + Quote(createIndexOperation.Columns[i]) + " " + sort + ",";
					}
					fields = fields.Substring(0, fields.Length - 1);
				}

				sql.Append(fields);
				sql.Append(")");

				// WHERE
				if (string.IsNullOrWhiteSpace(where) == false)
				{
					sql.Append(" WHERE ");
					sql.Append(where);
				}

				writer.Write(sql.ToString());
				Statement(writer);
			}
		}
	}
}

MyObject.cs

/**
 * Entity object
 */
public class MyObject {
  public int Id { get; set; }
  public string Type { get; set; }
  public DateTime DateFor { get; set; }
  public DateTime DateCreated { get; set; }
  public string Value { get; set; }
}

MyObjectMap.cs

using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity.Infrastructure.Annotations;
using System.Data.Entity.ModelConfiguration;

namespace X 
{
	public class MyObjectMap : EntityTypeConfiguration<MyObject>
	{
		public MyObjectMap()
		{
			// Index name in 3 parts:
			// 1st part: index name
			// 2nd part: Columns order separated by commas [optional]
			// 3rd part: WHERE clause of the index [optional]
			var indexName = "IX_Table:ASC,DESC,DESC:Type IS NOT NULL";
      
			this.Property(t => t.Type)
				.HasColumnAnnotation(
					IndexAnnotation.AnnotationName,
					new IndexAnnotation(new[]
						{
							new IndexAttribute(indexName) { Order = 1 }
						}
					)
				);

			this.Property(t => t.DateFor)
				.HasColumnAnnotation(
					IndexAnnotation.AnnotationName,
					new IndexAnnotation(new[]
						{
							new IndexAttribute(indexName) { Order = 2 }
						}
					)
				);

			this.Property(t => t.DateCreated)
				.HasColumnAnnotation(
					IndexAnnotation.AnnotationName,
					new IndexAnnotation(new[]
						{
							new IndexAttribute(indexName) { Order = 3 }
						}
					)
				);
		}
	}
}