one-to-many

I'm working on forum template using Flask. When I attempt creating a new thread in the browser using forms, SQLAlchemy throws an AttributeError. The problem showed up when I tried implementing a one-to-many relationship with Forum-to-Thread and a one-to-many relationship with Thread-to-User. models.py class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(32), index=True, unique=True) password = db.Column(db.String(32), index=True) email = db.Column(db.String(120), index=True, unique=True) role = db.Column(db.SmallInteger, default=ROLE_USER) posts =

I am reading currently the documentation of Hibernate regarding the entity associations and I come accross a little difficulty to figure out some things. It has to do in essence with the difference between ManyToOne and OneToMany associations. Although I have used them in real projects, I cannot apprehend completely the differnce between them. To my understanding, if a table / an entity has a ManyToOne association with another, then the association should be from the other side OneToMany . So, how should we decide which one to choose based on a specific case and how does it affect the database

I have 2 classes in a one-to-many relationship and a HQL query that is a bit strange. Even if I have read some questions already posted, it does not seem clear to me. Class Department{ @OneToMany(fetch=FetchType.EAGER, mappedBy="department") Set<Employee> employees; } Class Employee{ @ManyToOne @JoinColumn(name="id_department") Department department; } When I use the following query I get duplicates Department objects: session.createQuery("select dep from Department as dep left join dep.employees"); Thus, I have to use distinct: session.createQuery("select distinct dep from Department as dep

I have a question concerning Hibernate 3.6.7 and JPA 2.0. Consider following entities (some getters and setters are omitted for brevity): @Entity public class Parent { @Id @GeneratedValue private int id; @OneToMany(mappedBy="parent") private List<Child> children = new LinkedList<Child>(); @Override public boolean equals(Object obj) { return id == ((Parent)obj).id; } @Override public int hashCode() { return id; } } @Entity public class Child { @Id @GeneratedValue private int id; @ManyToOne private Parent parent; public void setParent(Parent parent) { this.parent = parent; } @Override public

I'm trying to set up a relationship as follows. Each Master item has one or more Detail items: public class Detail { public virtual Guid DetailId { get; set; } public virtual string Name { get; set; } } public class Master { public virtual Guid MasterId { get; set; } public virtual string Name { get; set; } public virtual IList<Detail> Details { get; set; } } And Mappings: public class MasterMap : ClassMap<Master> { public MasterMap() { Id(x => x.MasterId); Map(x => x.Name); HasMany(x => x.Details).Not.KeyNullable.Cascade.All(); } } public class DetailMap : ClassMap<Detail> { public DetailMap(

I'm using Hibernate with annotations (in spring), and I have an object which has an ordered, many-to-one relationship which a child object which has a composite primary key, one component of which is a foreign key back to the id of the parent object. The structure looks something like this: +=============+ +================+ | ParentObj | | ObjectChild | +-------------+ 1 0..* +----------------+ | id (pk) |-----------------| parentId | | ... | | name | +=============+ | pos | | ... | +================+ I've tried a variety of combinations of annotations, none of which seem to work. This is the

The error Cannot delete or update a parent row: a foreign key constraint fails. The classes class Teacher { /** *@ORM\OneToMany(targetEntity="publication", mappedBy="teacher") */ protected $publications; } class Publication { /** * @ORM\ManyToOne(targetEntity="Teacher", inversedBy="publications") * @ORM\JoinColumn(name="teacher_id", referencedColumnName="id") */ protected $teacher; } I want What I want is to make it that when you delete a teacher, the id_teacher is modified to NULL. I want to keep the publication but without reference to Professor. I don't know how do that in Doctrine, Is it