How do you ensure Cascade Delete is enabled on a table relationship in EF Code first?

Possible reason why you don’t get cascading delete is that your relationship is optional. Example:

public class Category
{
    public int CategoryId { get; set; }
}

public class Product
{
    public int ProductId { get; set; }
    public Category Category { get; set; }
}

In this model you would get a Product table which has a foreign key to the Category table but this key is nullable and there is no cascading delete setup in the database by default.

If you want to have the relationship required then you have two options:

Annotations:

public class Product
{
    public int ProductId { get; set; }
    [Required]
    public Category Category { get; set; }
}

Fluent API:

modelBuilder.Entity<Product>()
            .HasRequired(p => p.Category)
            .WithMany();

In both cases cascading delete will be configured automatically.

If you want to have the relationship optional but WITH cascading delete you need to configure this explicitely:

modelBuilder.Entity<Product>()
            .HasOptional(p => p.Category)
            .WithMany()
            .WillCascadeOnDelete(true);

Edit: In the last code snippet you can also simply write .WillCascadeOnDelete(). This parameterless overload defaults to true for setting up cascading delete.

See more on this in the documentation