I advise you to use: if beer.salas_set.filter(pk=sala.pk).exists(): # do stuff If you use sala in beer.salas_set.all() instead, it selects all records from the relation table and loops over them to find, whether the given object is there or not. However, beer.salas_set.filter(pk=sala.pk).exists() only selects zero or one row from the database and immediately gives the result … Read more
I would use the second junction table: MOVIE_CATEGORY_JUNCTION Movie_ID Category_ID The primary key would be the combination of both columns. You would also have a foreign key from each column to the Movie and Category table. The junction table would look similar to this: create table movie_category_junction ( movie_id int, category_id int, CONSTRAINT movie_cat_pk PRIMARY … Read more
Maybe something like this: select m.name from movies m inner join actors_movies am on m.id = am.movie_id inner join actors a on am.actor_id = a.id where a.name=”Christopher Walken”
I personally don’t use getters and setters whenever it’s possible (meaning : I don’t use any framework who needs it, like Struts for instance). I prefer writing immutable objects (public final fields) when possible, otherwise I just use public fields : less boiler plate code, more productivity, less side effects. The original justification for get/set … Read more
Figured it out. Here’s what I did: NSPredicate *predicate = [NSPredicate predicateWithFormat:@”lists.@count == 0″]; [fetchRequest setPredicate:predicate]; Then when I ran the fetch request, it only brought up the patients with no list attached.
The documentation says: If the association is bidirectional, one side has to be the owner and one side has to be the inverse end (ie. it will be ignored when updating the relationship values in the association table): So, the side which has the mappedBy attribute is the inverse side. The side which doesn’t have … Read more
It depends on how you search. If you search like this: /* Given a value from table1, find all related values from table2 */ SELECT * FROM table1 t1 JOIN table_table tt ON (tt.table_1 = t1.id) JOIN table2 t2 ON (t2.id = tt.table_2) WHERE t1.id = @id then you need: ALTER TABLE table_table ADD CONSTRAINT … Read more
From the comments I see you’ve found the answer. But the SQLAlchemy documentation is quite overwhelming for a ‘new user’ and I was struggling with the same question. So for future reference: ItemDetail = Table(‘ItemDetail’, Column(‘id’, Integer, primary_key=True), Column(‘itemId’, Integer, ForeignKey(‘Item.id’)), Column(‘detailId’, Integer, ForeignKey(‘Detail.id’)), Column(‘endDate’, Date)) class Item(Base): __tablename__ = ‘Item’ id = Column(Integer, primary_key=True) … Read more
My apologies, I finally stumbled across the answer in the SQLAlchemy docs… https://docs.sqlalchemy.org/en/latest/orm/basic_relationships.html#many-to-many …where they explicitly define the difference: Many to Many adds an association table between two classes. association_table = Table(‘association’, Base.metadata, Column(‘left_id’, Integer, ForeignKey(‘left.id’)), Column(‘right_id’, Integer, ForeignKey(‘right.id’)) ) The association object pattern is a variant on many-to-many: it’s used when your association table … Read more