Entity framework code first delete with cascade

Question

How do I set up my domain and the LINQ statement so I can delete a record from a database?

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

    public List<Product> Products{ get; set; }

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

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

What I'd like to do is delete Category and be able to cascade the delete to all the child products.

Is there any other additional attributes needed in my domain?
What is the LINQ statement to delete objects without doing a round trip? (I do not want to select, just a direct delete).

Is this the only way to do this?

Category category = new Category() {  CategoryId = 1   } ; 
context.AttachTo("Category", category);
context.DeleteObject(category);
context.Savechanges();

Community · Accepted Answer · 2017-05-23 12:02:02Z

41

You mentioned EF code first which means EF 4.1 but you have shown example of deleting object in EF 4. Correct approach to delete object in EF 4.1 without loading it from database is:

var category = new Category() { CategoryId = 1 };
context.Categories.Attach(category);
context.Categories.Remove(category);
context.SaveChanges();

If you didn't change anything in configuration of defalut conventions it will also delete all related products because OneToManyCascadeDeleteConventions ensures that all one-to-many relations are created with ON CASCADE DELETE. There will be no additional roundtrips to database - only single DELETE statement for Category with Id = 1.

The different situation can occure if you want to delete fully loaded Category (with loaded Products navigation property) in such case EF will create separate delete statement for each Product so you will have N+1 roundtrips to database where N is number of products in category. Here is how cascade delete works in EF. It is related to entity designer but described principles are the same.

edited May 23, 2017 at 12:02

CommunityBot

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answered Apr 2, 2011 at 9:43

Ladislav Mrnka

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9 Comments

Wil Over a year ago

+1 You are a godsend at the moment for me! Your answers seem to keep coming up on top of Google when searching for EF issues!.... RE: Your last paragraph - If I have an object which has a virtual property (a list) which has not been accessed/lazy loaded, and I have cascade delete on, will it send the one delete command, or will it then load the virtual property and then send multiples?

Ladislav Mrnka Over a year ago

@William: It should delete them without loading because deletion is handled by cascade delete in the database.

Chris Moschini Over a year ago

This has never worked for me in EF4.1, 4.3, or 5.0. Attempting to delete an EF Code First entity this way with one-to-many children consistently gets me the Exception: The DELETE statement conflicted with the REFERENCE constraint "FK_dbo.ChildTable_dbo.ParentTable_Parent_Id". The conflict occurred in database "Database", table "dbo.ChildTable", column 'Parent_Id'. The statement has been terminated.

Ladislav Mrnka Over a year ago

@Chirs: It means that your database doesn't have cascade delete defined on relationships. EF's ability for cascade delete is dependent on cascade delete configured in the database.

esde84 Over a year ago

@ChrisMoschini I too was coming up against this issue with EF 6.1.1 I found that adding the [Required] attribute to parent reference in the child class, got the delete cascade working for me.

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Vasil Popov · Accepted Answer · 2012-03-23 14:54:43Z

3

Taken from the VS2010 auto generated code:

Category category = db.Categories.Find(id);
db.Categories.Remove(category);
db.SaveChanges();

answered Mar 23, 2012 at 14:54

Vasil Popov

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2 Comments

Elad Benda Over a year ago

how come I don't have the method Remove?

Vasil Popov Over a year ago

You should have it here as the "db.Categories..." is of type DbSet<T>, which has the Remove method.

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