Common best practice for updating a record and its associated relationships in Linq-to-SQL

Question

I have a very general question about updating an entry in Linq-to-SQL. Suppose in my data model I have a base record (Table - Person) with a ratio of m: m to a set of categories (Table - Category). Therefore, I have an associative table (PersonCategory) that has foreign keys for both PersonID and CategoryID.

When I want to update Person, I may have new PersonCategory entries to add, and you might want to delete other PersonCategory entries. What is the best practice for doing this? Do I want to delete all entries in Person.RelatedPersonCategories and then add new ones? Is LINQ-to-SQL smart enough to negotiate which entries in the PersonCategory table are actually added, edited, or deleted (based on the potential potential potential infection of it)?

Thanks for any help!

Answer 1

DataContext , LINQ to SQL /update/delete rows , , , , DataContext.SubmitChanges().

:

using (var db = new DataContext())
{
    var person = db.Persons.Where(p => p.Name == "Foo").SingleOrDefault();

    if (person != null)
    {
        // Inserts a new row in the 'PersonCategory' table
        // associated to the current 'Person'
        // and to the 'Category' with name 'Employee'
        person.PersonCategories.Add(new PersonCategory() { CategoryName = "Employee" });

        // Updates the 'CategoryName' column in the first row
        // of the 'PersonCategory' table associated to the current 'Person'
        person.PersonCategories(0).CategoryName = "Consultant";

        db.SubmitChanges();
    }
}

, , DataContext, , .

/ , , , DataContext (TEntity).Attach, DataContext.SubmitChanges().

. , (TEntity).Attach .
MSDN:

, (, EntitySet ) . SubmitChanges, . , Attach .

:

// The 'Person' object has been detached
// from the originating 'DataContext', which is now disposed
person.PersonCategories.Add(new PersonCategory() { CategoryName = "Employee" });
person.PersonCategories(0).CategoryName = "Consultant";

using (var db = new DataContext())
{
    // Will detect added and deleted objects
    // in the 'PersonCategory' collection        
    db.Person.Attach(person);

    // Required to detect and modifications
    // to existing objects in the 'PersonCategory' collection
    foreach (var personCategory in person.PersonCategories)
    {
        db.PersonCategory.Attach(personCategory);
    }

    db.SubmitChanges();
}

Answer 2

. PersonCategory - , , , InsertOnSubmit() DeleteOnSubmit(). PersonCategory .

, , , .

, - , , .

,

• Person EntitySet<PersonCategory>

• PersonCategory EntityRef<Person> EntityRef<Category>

• Category EntitySet<PersonCategory>.

, , :

• Person PersonCategory null, EntitySet<PersonCategory> , PersonCategory EntitySet<PersonCategory>

• PersonCategory PersonCategory, Person Person.

, : LINQ to SQL , - .