many-to-many

问题 How to operate with many-to-many relationship in CoreData? For example: I have 2 entities - Recipes & Ingredients CoreData links them like Recipes <<-->> Ingredients. Now I need to add attribute "Count" for every Ingredient in Recipe. How can I do it? Thanks 回答1: Core Data takes care of the object graph consistency maintenance for you. So if you use a SQLite store, Core Data automatically creates the intermediate join table for you for many-to-many relationships. In your case, you should

问题 I have entity classes A and C. They are mapping the tables tblA and tblC and have a many-to-many relationship between them, with tblB to map between them. tblB contains A_ID, C_ID and SetDate, the last one being the date it was set, thus an attribute to the relationship. My question is, how do I best map in this attribute? At the moment they're unmapped, like this: A: @ManyToMany(targetEntity=C.class, cascade={ CascadeType.PERSIST, CascadeType.MERGE } ) @JoinTable(name="tblB", joinColumns=

问题 I am having some trouble with a many to many relationship. I have Users and Assets . I would like to be able to assign users to an asset on the asset page. The code below displays a list of users when creating/editing an asset, however changes made to the user checkboxes do not save, while the rest of the data is persisted. If I add an entry to users_assets through the mysql client, these changes are shown in the asset list. User class User extends BaseUser { /** * @ORM\ManyToMany

问题 I am having some trouble with a many to many relationship. I have Users and Assets . I would like to be able to assign users to an asset on the asset page. The code below displays a list of users when creating/editing an asset, however changes made to the user checkboxes do not save, while the rest of the data is persisted. If I add an entry to users_assets through the mysql client, these changes are shown in the asset list. User class User extends BaseUser { /** * @ORM\ManyToMany

问题 User-Friend relationship I find an answer Entity Framework Core: many-to-many relationship with same entity and try like this. Entitys: public class User { public int UserId { get; set; } public virtual ICollection<Friend> Friends { get; set; } } public class Friend { public int MainUserId { get; set; } public User ManUser { get; set; } public int FriendUserId { get; set; } public User FriendUser { get; set; } } The fluent API: modelBuilder.Entity<Friend>() .HasKey(f => new { f.MainUserId, f

问题 I have the following models: Client.rb has_many :establishments accepts_nested_attributes_for :establishments has_many :addressess, through: :establishments accepts_nested_attributes_for :addresses Establishment.rb belongs_to :address belongs_to :client Address.rb has_many :establishments On the show view of the Client I created a <%= link_to "New Establishment", new_client_address_path(@client)%> in order to create a new Address record and a new Establishment to the client. On the

问题 I Have a shoppinglist model which has many recipes, which again has many ingredients. class Shoppinglist < ActiveRecord::Base has_many :shoppinglistrecipezations has_many :recipes, :through => :shoppinglistrecipezations end class Recipe < ActiveRecord::Base has_many :shoppinglistrecipezations has_many :shoppinglists, :through => :shoppinglistrecipezations has_many :ingredients, :through => :ingredienzations has_many :ingredienzations end class Ingredient < ActiveRecord::Base has_many :recipes

问题 I have a class with several lazily initialized collections, both OneToMany and ManyToMany . The ManyToMany relationship is unidirectional, so the Expert class has no Project collection. @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "project") private List<Logging> loggings = new ArrayList<Logging>(); @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY) @JoinTable(name = "project_expert", joinColumns = { @JoinColumn(name = "project") }, inverseJoinColumns =

问题 I have a django model that is a message. It has a name which is a CharField, then also an array of users which is a ManyToManyField. So This is what my API looks like: [ { "id": 13, "content": "hej", "date": "2019-07-09", "sender": { "id": 1, "username": "william" } }, { "id": 14, "content": "hej william", "date": "2019-07-09", "sender": { "id": 3, "username": "ryan" } } ] What I've tried to send via postman POST: { "content": "Hello", "sender": {"username": "william"}, "date": "2019-09-02" }

问题 With this code i want to store multiple courses to the student table.But this code is not working.Neither it throws any error neither saves any data.The main problem is while clicking submit button the submit button does not perform any action at all.It does not load the submit button.How can i solve this?? I think the problem is in add_student.html template.When i return form.error it throws course.Is there anything i have to change??but i want to keep my design like this models.py class