Create a non-clustered index in Entity Framework Core

Question

Using Entity Framework Core, I want to have a Guid PK, without suffering page fragmentation in the database.

I have seen this post and this. Although it was possible in EF6, the way it's done seems to have changed.

Is it possible to create a non-clustered primary key in Entity Framework Core and have an additional index?

Q&A Answer below.

Answer 1

It is possible using EntityFrameworkCore v1.0.1 or greater.

The following code gets the desired result:

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;

namespace TestApplication.Models
{

    /// <summary>
    /// The context class. Make your migrations from this point.
    /// </summary>
    public partial class TestApplicationContext : DbContext
    {
        public virtual DbSet<Company> Companies { get; set; }

        public TestApplicationContext(DbContextOptions<TestApplicationContext> options) : base(options)
        {

        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            // standard stuff here...
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Company>(entity =>
            {
                entity.Property<Guid>("CompanyId")
                        .ValueGeneratedOnAdd();

                entity.Property<int>("CompanyIndex")
                        .UseSqlServerIdentityColumn()
                        .ValueGeneratedOnAdd();

                entity.Property(e => e.CompanyName)
                    .IsRequired()
                    .HasColumnType("varchar(100)");

                // ... Add props here.

                entity.HasKey(e => e.CompanyId)
                    .ForSqlServerIsClustered(false)
                    .HasName("PK_Company");
                entity.HasIndex(e => e.CompanyIndex)
                    .ForSqlServerIsClustered(true)
                    .HasName("IX_Company");
            });
        }
    }

        /// <summary>
        /// The model - put here for brevity.
        /// </summary>
        public partial class Company
        {
            public Company()
            {
            }

            public Guid CompanyId { get; set; }
            public int CompanyIndex { get; set; }

            public string CompanyName { get; set; }
            // more props here.
        }

    }

Project.json

{
    "version": "1.0.0-*",

    "dependencies": {
        "Microsoft.EntityFrameworkCore.Design": "1.0.1",
        "Microsoft.EntityFrameworkCore.SqlServer": "1.0.1",
        "Microsoft.EntityFrameworkCore.SqlServer.Design": "1.0.1",
        "Microsoft.EntityFrameworkCore.Tools": "1.0.0-preview3-final",
        "NETStandard.Library": "1.6.0"
    },
    "tools": {
        "Microsoft.EntityFrameworkCore.Tools": "1.0.0-preview3-final",
        "Microsoft.AspNetCore.Server.IISIntegration.Tools": "1.0.0-preview2-final"
    },
    "frameworks": {
        "netstandard1.6": {
            "imports": "dnxcore50"
        }
    }
}

Answer 2

For EF Core 5 or greater

  // ...
  modelBuilder.Entity<MyEntity>(entity =>
  {
     // ...
     entity.HasIndex(e => e.MyIndexColumn)
       .IsClustered(false);
  }
  // ...

=> The obsolete method ForSqlServerIsClustered was removed in this version

For EF Core 3.x

  // ...
  modelBuilder.Entity<MyEntity>(entity =>
  {
     // ...
     entity.HasIndex(e => e.MyIndexColumn)
       .IsClustered(true); // new method
     // OR
     entity.HasIndex(e => e.MyIndexColumn)
       .ForSqlServerIsClustered(false); // obsolete method
  }
  // ...

=> Both methods IsClustered and ForSqlServerIsClustered can be used, but later one is already marked as obsolete in favor of the first one.

For EF Core 1.x- EF Core 2.x

  // ...
  modelBuilder.Entity<MyEntity>(entity =>
  {
     // ...
     entity.HasIndex(e => e.MyIndexColumn)
       .ForSqlServerIsClustered(false);
  }
  // ...