Entity Framework Code first : Set unique key constraint is not working

Question

In my application I am using EntityFramework with code first approach. I am using EF7 with ASP.NET 4.6 MVC and VS2015. My model class is like below :

public class Customer
{
    public int CustomerID { get; set; }

    [StringLength(100)]
    [Required]
    public string FirstName { get; set; }

    [StringLength(100)]
    [Required]
    public string LastName { get; set; }

    [Required]
    [EmailAddress(ErrorMessage = "Please enter valid Email Address.")]
    [StringLength(100)]
    [Index("IX_EA", IsUnique = true)]
    public string EmailAddress { get; set; }

}

My context file is like below :

public class CustomerContext : DbContext
{
    public CustomerContext()
    {
        Database.EnsureCreated();
    }
    public DbSet<Customer> Customers { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder options)
    {    
        var connection = System.Configuration.ConfigurationManager.ConnectionStrings["DbConnectionString"].ConnectionString;
        options.UseSqlServer(connection).UseRowNumberForPaging();
    }
}

So, from model class you can see that I want set unique constraint to EmailAddress column in database table means EmailAddress field should contain duplicate value(an email address should not be repeat in table). But when I run the project database successfully get created. but that Unique constraint in not there. I am not getting why it is not setting that constraint on EmailAddress field.

Please help me to set unique constraint to the field using code first approach of EntityFramework.

Answer 1

From EF Core Documentation:

Indexes can not be created using data annotations.

But you can use the fluent API to create index :

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Customer>()
        .HasIndex(c => c.EmailAddress) // Create an index
        .IsUnique() // that is unique
        .ForSqlServerHasName("IX_EA"); // specify the name 
}

You can also use Alternate keys

An alternate key serves as a alternate unique identifier for each entity instance in addition to the primary key. When using a relational database this maps to the concept of a unique index/constraint. In EF, alternate keys provide greater functionality than unique Indexes because they can be used as the target of a foreign key.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Customer>()
        .HasAlternateKey(c => c.EmailAddress);
}