entity-relationship

I have a one to many relationship in my core data model. I need to create a new entity and save it. The entity has a one to many relationship which generated the following code: - (void)addRelationshipEvent1:(NSSet *)values; - (void)removeRelationshipEvent1:(NSSet *)values; . NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext]; NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity]; ApplicationRecord *newManagedObject = (ApplicationRecord*)[NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext

In every tutorial on entity relationship diagrams, I read that specifying a fixed cardinality for a relationship is not allowed. Only an informal comment on the ERD may clarify that the number of pilots is exactly 2 . So, for example, a relationship between flights and pilots where each flight has exactly 2 pilots present, would have to be represented as: <flight> 0..N <------> 1..N <pilot> rather than <flight> 0..N <------> 2 <pilot> My notation is 0..N = optional, many; 1..N = mandatory, many, 1 = mandatory, one. Is this restriction universal? What's the reason behind it? EDIT: clarified my

I am having problem with saving the changes to database. I am updating the model A in my controller, however when I save the changes using SaveChanges() I end up having a duplicated item in database for B. After the UpdateModel() is called I inspected the Bs property and it was as I expected however right after the SaveChanges() is called if I inspect the Bs property I will see that the Id is completely different (new Id and new entry). My class is similar to this: public class A { [HiddenInput(DisplayValue = false)] public int AId { get; set; } public string Name { get; set; } public virtual

Good day everyone! I have a question about collection persistence in Symfony and Doctrine The short version I can add an item to collection (persist) via form, but can not remove (remove). The logics I need a possibility to add users to business trips. Each added user must have text description (like a objective for business trip). In fact, i have 3 entities: BusinessTrip BusinessTripUser (stores linked User id, BusinessTrip id and text field "description") User (vendor bundle entity) The problem As i already said above - i cant remove BusinessTripUser from collection $users in BusinessTrip. I

I have a situation in a service method where assigning a POCO as a child object of another POCO does not work as expected. I am using Entity Framework 4. public void ChangeOrderCurrency(Currency currency) { order.CurrencyId = currency.Id; order.Currency = currency; // other stuff related to exchange rates etc } Which is more correct to use to set the relationship? order.CurrencyId = currency.Id or order.Currency = currency ? In this current code which passes all unit tests, occasionally the line order.Currency = currency will set both order.CurrencyId and order.Currency to NULL It makes more

In the EER model there are subclasses entities. I was wondering what's the way to implement that in a real SQL Table or if there is any guide that might help me out to understand how to implement entities subclasses into tables that would help. Thanks Martin Fowler's book Patterns of Enterprise Application Architecture covers solutions for subclassing tables: Single Table Inheritance Class Table Inheritance Concrete Table Inheritance These correspond to the options in the answer from @spencer7593, without being tied to Java & Hibernate. The Hibernate documentation has discussion of the options