Can I use Data Annotations to perform a Cascade Delete with Entity Framework 4.1 RC?

Question

When using data annotations with EF4.1 RC is there an annotation to cause cascade deletes?

public class Category
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    public ICollection<Product> Products { get; set; }
}

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Category Category { get; set; }
}

Using this model the constraint generated is:

ALTER TABLE [Product] ADD CONSTRAINT [Product_Category] 
FOREIGN KEY ([Category_Id]) REFERENCES [Categorys]([Id]) 
ON DELETE NO ACTION ON UPDATE NO ACTION;

If not how is it achieved?

Solution 1

Putting required on the Product table Category relationship field solves this

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }

    [Required]  //<======= Forces Cascade delete
    public Category Category { get; set; }
}

Solution 2

I like to turn off cascade delete by default (by removing the OneToManyCascadeDeleteConvention)

I was then hoping to add them back in via annotations, but was surprised that EF doesn't include a CascadeDeleteAttribute.

After spending way too long working around EF's ridiculous internal accessor levels, the code in this gist adds a convention that allows attributes to be used: https://gist.github.com/tystol/20b07bd4e0043d43faff

To use, just stick the [CascadeDelete] on either end of the navigation properties for the relationship, and add the convention in your DbContext's OnModeCreating callback. eg:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
    modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
    modelBuilder.Conventions.Add<CascadeDeleteAttributeConvention>();
}  

And in your model:

public class BlogPost
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    [CascadeDelete]
    public List<BlogPostComment> Comments { get; set; } 
}

Solution 3

Not sure on Data Annotations, but you can add it in the database by modifying the actual relationship.

Looks like the answer is no for data annotations: http://social.msdn.microsoft.com/Forums/en-US/adonetefx/thread/394821ae-ab28-4b3f-b554-184a6d1ba72d/

This question appears to show how to do it with the fluent syntax, but not sure if that applies for 4.1 RC EF 4.1 RC: Weird Cascade Delete

Solution 4

As an additional example to Tyson's answer, I use the [CascadeDelete] attribute like follows in an entity, which successfully adds the "Cascade" delete rule to the Parent-Child relation.

public class Child
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Key]
    [SkipTracking]
    public Guid Id { get; set; }

    [CascadeDelete]
    public virtual Parent Parent { get; set; }

    [Required]
    [ForeignKey("Parent")]
    public Guid ParentId { get; set; }
}

View more solutions

Comments

[Rafael]

This is better than the chosen answer because the Requiered attribute imples a not-nullable foreign key. And it works with EF 6. Thanks!

[Alireza]

Great solution, also, please note that the Convention class should be added to the modelBuilder.Conventions in OnModelCreating method.

[Elias MP]

Very creative. Thanks.

[Shimmy Weitzhandler]

What gets deleted upon deletion of what?

[Derrick]

This only seems to work on [Required] relationships, so in my case I modified CascadeDeleteAttribute to inherit from RequiredAttribute for clarity

[KlevisGjN]

Searching for ef core foreign key annotation cascade delete found nothing. Your comment worked as expected. Thanks