Setting unique Constraint with fluent API?

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On EF6.2, you can use HasIndex() to add indexes for migration through fluent API.

https://github.com/aspnet/EntityFramework6/issues/274

Example

modelBuilder
    .Entity<User>()
    .HasIndex(u => u.Email)
        .IsUnique();

On EF6.1 onwards, you can use IndexAnnotation() to add indexes for migration in your fluent API.

http://msdn.microsoft.com/en-us/data/jj591617.aspx#PropertyIndex

You must add reference to:

using System.Data.Entity.Infrastructure.Annotations;

Basic Example

Here is a simple usage, adding an index on the User.FirstName property

modelBuilder 
    .Entity<User>() 
    .Property(t => t.FirstName) 
    .HasColumnAnnotation(IndexAnnotation.AnnotationName, new IndexAnnotation(new IndexAttribute()));

Practical Example:

Here is a more realistic example. It adds a unique index on multiple properties: User.FirstName and User.LastName, with an index name “IX_FirstNameLastName”

modelBuilder 
    .Entity<User>() 
    .Property(t => t.FirstName) 
    .IsRequired()
    .HasMaxLength(60)
    .HasColumnAnnotation(
        IndexAnnotation.AnnotationName, 
        new IndexAnnotation(
            new IndexAttribute("IX_FirstNameLastName", 1) { IsUnique = true }));

modelBuilder 
    .Entity<User>() 
    .Property(t => t.LastName) 
    .IsRequired()
    .HasMaxLength(60)
    .HasColumnAnnotation(
        IndexAnnotation.AnnotationName, 
        new IndexAnnotation(
            new IndexAttribute("IX_FirstNameLastName", 2) { IsUnique = true }));

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