many-to-many

问题 I try associate 2 existing Many-to-Many records with ECTO and put_assoc/4 but won't remove elements when try update. Basically i have projects and users . for manage the access of users to projects i have the table "user_project". def Project do schema "project" do ... # users (if user_type is :admin) many_to_many( :users, User, join_through: "user_project" ) ... end end def User do schema "user" do ... # users (if user_type is :admin) many_to_many( :projects, User, join_through: "user

问题 So I asked this question yesterday, but the goal posts have changed and the question is different: Hibernate / JPA Collection of Elements with Many to Many relationship? I want to know if it's possible to create entities that will model my required relationship so that Hibernate will create my schema when I fire up my application. The relationship I want looks like this: 1 http://a8.sphotos.ak.fbcdn.net/hphotos-ak-ash4/417593_10150594114269218_505554217_8657377_1475865815_n.jpg The thing is

问题 I need to create my own intermediate model. class class1(models.Model) class class2(models.Model): field1 = models.ManyToManyField(class1, through="class3") class class3(models.Model): field1 = models.ForeignKey(class1) field2 = models.ForeignKey(class2) field3 = models.IntegerField() class Meta: auto_created = True I use "auto_created=True" because in the following code, I had the error : AttributeError: Cannot use add() on a ManyToManyField which specifies an intermediary model. for m2m

问题 I am facing problem while saving a record when i have an extra column in the mapping table in case of manytomany relationship. Please see below for details. There is manytomany relationship between User and BankAccounts. The mapping table for user_bankaccounts has an extra column called user_type, apart from the primary keys of User and BankAccount table. However, when i try to save a bank account record, mapping table data is not inserted in the user_bankaccount table. Only bankaccount table

问题 I have many to many relation ship between User and Roles. For example public class User { @Id private Integer id; @ManyToMany @JoinTable(name = "APP_USER_ROLE", joinColumns = { @JoinColumn(name = "USER_ID") }, inverseJoinColumns = { @JoinColumn(name = "ROLE_ID") }) private List<Role> roles = new ArrayList<Role>(); } @Entity public class Role { @Id private Integer id; @ManyToMany(mappedBy = "roles") private List<User> users = new ArrayList<User>(); } My requirement is to fetch all users in the

问题 This is baffling me... When I save my model, the book objects are unchanged. But if I open the invoice and save it again, the changes are made. What am I doing wrong? class Invoice(models.Model): ... books = models.ManyToManyField(Book,blank=True,null=True) ... def save(self, *args, **kwargs): super(Invoice, self).save(*args, **kwargs) for book in self.books.all(): book.quantity -= 1 if book.quantity == 0: book.sold = True; book.save() Edit: I've tried using the post_save signal, but it works

问题 I have few similar models in Django: class Material(models.Model): title = models.CharField(max_length=255) class Meta: abstract = True class News(Material): state = models.PositiveSmallIntegerField(choices=NEWS_STATE_CHOICES) class Article(Material): genre = models.ForeignKey(Genre, verbose_name='genre') And model Topic , which is related to News and Article as ManyToMany. I'd like to use Generic many-to-many relationships like in this case. But question is how to use default ManyToMany

问题 I have a SQL table like so: Update: I'm changing the example table as the existing hierarchical nature of the original data (State, Cities, Schools) is overshadowing the fact that a simple relationship is needed between the items. entities id name 1 Apple 2 Orange 3 Banana 4 Carrot 5 Mushroom I want to define two-way relationships between these entities so a user viewing one entity can see a list of all related entities. The relationships are defined by an end user. What is the best way to

问题 I want to implement a Role Hierarchy but am rather new to JPA Annotations. I have a Role Entity with a name and an id(implicit via AbstractPersistable ): @Entity @Table(name="role") public class Role extends AbstractPersistable<Long> { private static final long serialVersionUID = 8127092070228048914L; private String name; Now I want to be able to define the following relationships: a Role can have many child roles a Role can be child to many roles How would I do that with Hibernate

问题 I want to implement a Role Hierarchy but am rather new to JPA Annotations. I have a Role Entity with a name and an id(implicit via AbstractPersistable ): @Entity @Table(name="role") public class Role extends AbstractPersistable<Long> { private static final long serialVersionUID = 8127092070228048914L; private String name; Now I want to be able to define the following relationships: a Role can have many child roles a Role can be child to many roles How would I do that with Hibernate