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
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
JamesO is correct – it looks like your Category.articles field has a through relationship. Assuming that your models at least resemble the following class Article(models.Model): name = models.CharField(max_length=128) class Category(models.Model): name = models.CharField(max_length=128) articles = models.ManyToManyField(Article, through=”Membership”) class Membership(models.Model): article = models.ForeignKey(Article) category = models.ForeignKey(Category) author = models.CharField() then to add an Article to a … Read more
This is a simple and a very fundamental question to EF Core many-to-many relationship; I do not know why no one has written a complete example for n..m in EF Core. I have modified your code (primary key as int), I do not like string in primary key. Just copy/paste the code and every should … Read more
By convention, Code First will take uni-directional associations as one to many. Therefore you need to use fluent API to let Code First know that you want to have a many to many self referencing association: protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<Member>().HasMany(m => m.Friends).WithMany().Map(m => { m.MapLeftKey(“MemberId”); m.MapRightKey(“FriendId”); m.ToTable(“MembersFriends”); } ); }
The detach method is used to release a relationship from the pivot table, whilst delete will delete the model record itself i.e. the record in the reviews table. My understanding is that delete won’t trigger the detach implicitly. You can use model events to trigger a cleanup of the pivot table, though, using something like: … Read more
You can use: space.related.all() to return a QuerySet of User
The easiest way is just to pass the band to the template. Templates are capable of navigating the relationships between models and there is both members and membership_set queryset managers on Group. So here is how I would do it: view: def group_details(request, group_id): group = get_object_or_404(Group, pk=group_id) return render_to_response(‘group_details.html’, {‘group’: group}) template: <h2>{{ group.name … Read more
It’s possible with this little trick (OUTER JOIN on the many-to-many table, with the constraint that the GroupID has to be 3 (for Drama) http://sqlfiddle.com/#!9/01cf3/1 SELECT elements.ID, elements.Element, groups.Genre FROM elements LEFT OUTER JOIN group_elements ON elements.ID = group_elements.ElementID AND group_elements.GroupID = 3 LEFT OUTER JOIN groups ON group_elements.GroupID = groups.ID LEFT OUTER JOIN means … Read more