How to create index in Entity Framework 6.2 with code first

Question

Is there a way to create an index on a property/column using code-first, instead of using the new IndexAttribute ?

Answer 1

Without an explicit name:

[Index]
public int Rating { get; set; } 

With a specific name:

[Index("PostRatingIndex")] 
public int Rating { get; set; }

Answer 2

From EF 6.1 onward the attribute [Index] is supported.
Use [Index(IsUnique = true)] for unique index.
Here is the link from Microsoft

public class User 
{ 
    public int UserId { get; set; } 

    [Index(IsUnique = true)] 
    [StringLength(200)] 
    public string Username { get; set; } 

    public string DisplayName { get; set; } 
}

Answer 3

Currently there is no "first class support" for creating a index via the fluent API, but what you can do is via the fluent API you can mark properties as having attributes from the Annotation API. This will allow you to add the Index attribute via a fluent interface.

Here are some examples from the work item from Issues site for EF.

Create a index on a single column:

modelBuilder.Entity<MyEntity>()
    .Property(e => e.MyProperty)
    .HasColumnAnnotation(
        IndexAnnotation.AnnotationName, 
        new IndexAnnotation(new IndexAttribute()));

Multiple indexes on a single column:

modelBuilder.Entity<MyEntity>()
    .Property(e => e.MyProperty)
    .HasColumnAnnotation(
        IndexAnnotation.AnnotationName, 
        new IndexAnnotation(new[]
            {
                new IndexAttribute("Index1"),
                new IndexAttribute("Index2") { IsUnique = true }
            }));

Multi-Column indexes:

modelBuilder.Entity<MyEntity>()
    .Property(e => e.MyProperty1)
    .HasColumnAnnotation(
        IndexAnnotation.AnnotationName,
        new IndexAnnotation(new IndexAttribute("MyIndex", 1)));

modelBuilder.Entity<MyEntity>()
    .Property(e => e.MyProperty2)
    .HasColumnAnnotation(
        IndexAnnotation.AnnotationName, 
        new IndexAnnotation(new IndexAttribute("MyIndex", 2)));

Using the above techniques will cause .CreateIndex() calls to be automatically created for you in your Up() function when you scaffold your next migration (or be automatically created in the database if you are not using migrations).

Answer 4

I write an extension method for use in fluent EF to avoid extra code:

public static PrimitivePropertyConfiguration HasIndexAnnotation(
    this PrimitivePropertyConfiguration primitivePropertyConfiguration, 
    IndexAttribute indexAttribute = null
    )
{
    indexAttribute = indexAttribute ?? new IndexAttribute();

    return primitivePropertyConfiguration
        .HasColumnAnnotation(
            IndexAnnotation.AnnotationName, 
            new IndexAnnotation(indexAttribute)
        );
}

then use it like this:

Property(t => t.CardNo)
    .HasIndexAnnotation();

or like this if index needs some configs:

Property(t => t.CardNo)
    .HasIndexAnnotation(new IndexAttribute("IX_Account") { IsUnique = true });