EDIT 2017-04-29: As pointed to by some of the commenters, the JoinTable example does not need the mappedBy annotation attribute. In fact, recent versions of Hibernate refuse to start up by printing the following error: org.hibernate.AnnotationException: Associations marked as mappedBy must not define database mappings like @JoinTable or @JoinColumn Let’s pretend that you have an … Read more
If you want to create many to many relationship with additional data in association table, you have to make the association table as entity. The pure many to many relationship is only in pure table with entity id’s. In you case it will be: public class Media // One entity table { public int Id … Read more
In terms of entities (or objects) you have a Class object which has a collection of Students and a Student object that has a collection of Classes. Since your StudentClass table only contains the Ids and no extra information, EF does not generate an entity for the joining table. That is the correct behaviour and … Read more
To explain it simply, when you are loading an entity and if it has an association with one or more entities, what should doctrine do? If the association is marked as EAGER, it will fetch and load the associated entity as well. If the association is marked as LAZY, doctrine will create proxy objects (dummy … Read more
(Update: For Django 1.2 and newer, which can follow select_related queries across reverse OneToOneField relations (and thus down inheritance hierarchies), there’s a better technique available which doesn’t require the added real_type field on the parent model. It’s available as InheritanceManager in the django-model-utils project.) The usual way to do this is to add a ForeignKey … Read more
Since the SERVICE_USER table is not a pure join table, but has additional functional fields (blocked), you must map it as an entity, and decompose the many to many association between User and Service into two OneToMany associations : One User has many UserServices, and one Service has many UserServices. You haven’t shown us the … Read more
The related_name attribute specifies the name of the reverse relation from the User model back to your model. If you don’t specify a related_name, Django automatically creates one using the name of your model with the suffix _set, for instance User.map_set.all(). If you do specify, e.g. related_name=maps on the User model, User.map_set will still work, … Read more
The SQL DDL (data definition language) statements could look like this: CREATE TABLE product ( product_id serial PRIMARY KEY — implicit primary key constraint , product text NOT NULL , price numeric NOT NULL DEFAULT 0 ); CREATE TABLE bill ( bill_id serial PRIMARY KEY , bill text NOT NULL , billdate date NOT NULL … Read more
It’s not possible to create a many-to-many relationship with a customized join table. In a many-to-many relationship EF manages the join table internally and hidden. It’s a table without an Entity class in your model. To work with such a join table with additional properties you will have to create actually two one-to-many relationships. It … Read more