# IT:AD:EF/CodeFirst:HowTo:Define Models/Unique Indexes #



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<panel title="Summary"> 
The following was possible before EF6.1 which came out in March 2014.


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## Process ##

Define a Map, using `HasColumnAnnotation` to add `Index` to *n* columns (note the numbering...)

<sxh csharp>
namespace XAct.Spikes.CodeFirst
{
    using System.ComponentModel.DataAnnotations.Schema;
    using System.Data.Entity.Infrastructure.Annotations;
    using System.Data.Entity.ModelConfiguration;

    public class SerializedSettingMap : EntityTypeConfiguration<SerializedSetting>
    {
        public SerializedSettingMap()
        {
            this.ToTable("Settings");
            this.HasKey(x => x.Id);
            
            this.Property(x => x.Id)
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);

            this.Property(x => x.Env)
                .IsRequired()
                .HasMaxLength(32)
                .HasColumnAnnotation(
                    "Index",
                    new IndexAnnotation(
                        new IndexAttribute("IX_EnvAppZoneHostKey", 1) { IsUnique = true }));
            this.Property(x => x.App)
                .IsRequired()
                .HasMaxLength(32)
                .HasColumnAnnotation(
                    "Index",
                    new IndexAnnotation(
                        new IndexAttribute("IX_EnvAppZoneHostKey", 2) { IsUnique = true }));
            
            this.Property(x => x.Zone)
                .IsRequired()
                .HasMaxLength(32)
                .HasColumnAnnotation(
                    "Index",
                    new IndexAnnotation(
                        new IndexAttribute("IX_EnvAppZoneHostKey", 3) { IsUnique = true }));

            this.Property(x => x.Host)
                .IsRequired()
                .HasMaxLength(32)
                .HasColumnAnnotation(
                    "Index",
                    new IndexAnnotation(
                        new IndexAttribute("IX_EnvAppZoneHostKey", 4) { IsUnique = true }));

            this.Property(x => x.Key)
                .IsRequired()
                .HasMaxLength(128)
                .HasColumnAnnotation(
                    "Index",
                    new IndexAnnotation(
                        new IndexAttribute("IX_EnvAppZoneHostKey", 5) { IsUnique = true }));
        }
    }
}</sxh>


## Resources ##


* http://stackoverflow.com/questions/21573550/entity-framework-6-setting-unique-constraint-with-fluent-api
* http://blog.oneunicorn.com/2014/02/15/ef-6-1-creating-indexes-with-indexattribute/