many-to-many

From the Django documentation... When you're only dealing with simple many-to-many relationships such as mixing and matching pizzas and toppings, a standard ManyToManyField is all you need. However, sometimes you may need to associate data with the relationship between two models. For example, consider the case of an application tracking the musical groups which musicians belong to. There is a many-to-many relationship between a person and the groups of which they are a member, so you could use a ManyToManyField to represent this relationship. However, there is a lot of detail about the

I have a object with a many-to-many relation with another object. In the Django Admin this results in a very long list in a multiple select box. I'd like to filter the ManyToMany relation so I only fetch Categories that is available in the City that the Customer have selected. Is this possible? Will I have to create a widget for it? And if so - how do I copy the behavior from the standard ManyToMany field to it, since I would like the filter_horizontal function as well. These are my simplified models: class City(models.Model): name = models.CharField(max_length=200) class Category(models.Model

With the following models: class OrderOperation(models.Model): ordered_articles = models.ManyToManyField(Article, through='orders.OrderedArticle') class OrderedArticle(models.Model): order_operation = models.ForeignKey(OrderOperation) article = models.ForeignKey(Article) articles = ... # some queryset containing multiple articles If I want to find order operations containing at least one article, this works as expected: OrderOperation.objects.filter(ordered_articles__in=articles) However, if I want to find order operations with all the articles in the order, what is the correct way to do it?

I am using JPA with Hibernate as the implementation in my Spring webapp. I use EntityListener s for auditing (Spring-data) and other notification purposes. In general it works fine. However, when changes are made to a many-to-many collection/relationship, without any other change to any field of the entities themselves , the @PostUpdate event of the EventListener s are not fired. To give a concrete example : I have a User and a Role entities, with a many-to-many relationship between them, using an underlying table. If I go to my user management GUI, and add (or remove) roles to a user, without

I have created an entity type that has multiple collection properties that reference items of the same type. In other words, it reflects a single database table in which the rows are arbitrarily grouped, such that a row may appear in multiple groups. In the following simplified example, the Person class has Brothers and Sisters collection properties that also reference Person entities: public class Person { public Person() { Brothers = new Collection<Person>(); Sisters = new Collection<Person>(); } [Key] public string Name { get; set; } public int Age { get; set; } public virtual ICollection

I have the following code in my models: Class Farm < ActiveRecord::Base has_many :farm_products, :dependent => :destroy has_many :products, :through => :farm_products accepts_nested_attributes_for :farm_products end class Product < ActiveRecord::Base has_many :farm_products, :dependent => :destroy has_many :farms, :through => :farm_products end class FarmProduct < ActiveRecord::Base belongs_to :farm belongs_to :product end I have a form to create a new Farm, and I want to create farm_products along with this form. My farm_products table can not only contain foreign key fields. How can I add or