asp.NET LINQ从数据库中删除

Question

I have a SQL Server database with 2 tables:

t1 - Category

Id
Name

t2- Product

Id
Name
CategoryId

I want to delete a row from the Category table, but since I have the foreign key I need to handle the products that has the CategoryId I want to delete.

So I did this:

var ProdCatID = (from prod in DataContext.Products
                 where prod.CategoryId == Convert.ToInt32(Id)
                 select prod).First();

ProdCatID.CategoryId = null;
DataContext.SubmitChanges();

var DelCat = (from cat in DataContext.Categories
             where cat.Id == Convert.ToInt32(Id)
             select cat).ToList();

DataContext.Categories.DeleteAllOnSubmit(DelCat);
DataContext.SubmitChanges();

What I m trying to do is to check if there is any product with that CategoryId , if there is - I want to set the CategoryID to null and then delete the row from the Category` table.

It is working when I have a product with a CategoryId but when I can't delete it.

Any ideas?

Answer 1

You're only setting the first product that has this CategoryID to null - you need to handle all products that have that ID !

var products = (from prod in DataContext.Products
                where prod.CategoryId == Convert.ToInt32(Id)
                select prod).ToList();

foreach(Product p in products)
{
    p.CategoryId = null;
}

DataContext.SubmitChanges();

.....

After that, now you should be able to delete the category from the table

Answer 2

Simple! Change the Product table configuration in Database!

ALTER TABLE Product 
ADD CONSTRAINT 'Category_FK'
    FOREIGN KEY (CategoryId)
    REFERENCES Category(Id)
    ON DELETE SET NULL;

whenever you delete a primary key will automatically put null!

Answer 3

Cascade on Delete is there in entity framework. Cascade delete automatically deletes dependent records or set null to foreignkey properties when the principal record is deleted.

This is one to many reletionship between parent and child

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{   
    modelBuilder.Entity<User>()
        .HasOptional(a => a.UserDetail)
        .WithOptionalDependent()
        .WillCascadeOnDelete(true);
}

For more details check this: http://www.entityframeworktutorial.net/code-first/cascade-delete-in-code-first.aspx