many-to-many

OK, no matter how I define these mappings, my many-to-many mapping does not want to work with cascade insert. I have tried various combination of Cascade() with Reverse() and removing all unnecessary properties just to understand if they had anything to do with this not working, but no lock. It is really Simple stuff: I have a Message (like an email) which is sent from a user (I have called the entity BasicUser ) to a number of users (through property To ). User and Message in terms of recipients have a many-to-many relationship but FromUser has one-to-many. FromUser works fine and it is

I have an entity mapped as following: @Entity @Table(name = "Groups") @IdClass(value = GroupId.class) public class Group implements Serializable { @Id @Column(name = "round_id") private Integer roundId; @Id @Column(name = "ordinal_nbr") private Integer ordinalNbr = 0; ... } It has a composite key (round_id, ordinal_nbr) to indicate the order of groups in a round. Now imagine a join table containing entities that link the ordered groups via a self reference (from Group to Group): CREATE TABLE GroupLinks ( parent_round_id INTEGER NOT NULL, parent_ordinal_nbr SMALLINT NOT NULL, child_round_id

I can lazy load one-to-many and many-to-one associations but I can't with the many-to-many associations. We have a city in wich we have merchants wich have adresses. Merchants can have multiple addresses and multiple merchants can have the same addresses. When we load a merchant with a get, Merchant merchant = (Merchant) hib_session.get(Merchant.class, id); System.out.println(merchant.getName()); it's ok, addresses aren't load until we iterate over them. But when we load a list of merchants, City city = (City) hib_session.get(City.class, city_name); for(Merchant merchant : city.getMerchants())

I have Peticion entity but something is missing because appears the following error: No identifier/primary key specified for Entity (...) Every Entity must have and identifier/primary key This is the entity code: <?php namespace Project\UsuarioBundle\Entity; use Doctrine\ORM\Mapping as ORM; /** * Peticion * * @ORM\Table(name="peticion") * @ORM\Entity */ class Peticion { /** * * @ORM\Id * @ORM\ManyToMany(targetEntity="Project\UsuarioBundle\Entity\Usuario", inversedBy="usuNick2") * @ORM\JoinTable(name="USUARIO", * joinColumns={@ORM\JoinColumn(name="USU_NICK_1", referencedColumnName="USU_NICK")},

Django's ManyToMany field can be populated using my_field.add(my_instance) , but as I understand it only my_instance.id is actually needed to perform the corresponding SQL query. If I want to add an object by its id, I can use my_field.add(MyModel.objects.get(id=id)) , but this will generate two queries instead of one. How can I avoid this extra query? Although the documentation of the add method does not mention it, you can actually pass directly an id to it, like this: my_instance.add(id) Surely, this only works when the primary key is used as the identifier for the relation (the default

How can you create models (and thus tables) with a compound (composite) primary/unique key using Django? Django does not support compound primary keys. You can create a single compound unique key with Meta.unique_together . if you want only unique mixed fields together use belowcode: class MyTable(models.Model): class Meta: unique_together = (('key1', 'key2'),) key1 = models.IntegerField() key2 = models.IntegerField() But if you want unique together and one of column be primary, set primary argument for model column, similar below code: class MyTable(models.Model): class Meta: unique_together