many-to-one

问题 I hope someone can help me find an answer. I'm working with a legacy database and I can't change any of the preexisting tables, because other apps depend on them. I have three main existing tables: A,B,C . A has a column with reference to B(many to one relation). The problem is that it should have a relation to C not to B. So I have created a *-1 mapping BC. Tables: A,B,C,BC (all have ID field) A-B many to one B-C many to one through BC Needed:A-C without altering A,B or C I don't want to

问题 I hope someone can help me find an answer. I'm working with a legacy database and I can't change any of the preexisting tables, because other apps depend on them. I have three main existing tables: A,B,C . A has a column with reference to B(many to one relation). The problem is that it should have a relation to C not to B. So I have created a *-1 mapping BC. Tables: A,B,C,BC (all have ID field) A-B many to one B-C many to one through BC Needed:A-C without altering A,B or C I don't want to

问题 I'm having difficulty representing this query (which works on the database directly) as a criteria query in Hibernate (version 3.2.5): SELECT s.* FROM ftp_status s WHERE (s.datetime,s.connectionid) IN (SELECT MAX(f.datetime), f.connectionid FROM ftp_status f GROUP BY f.connectionid); so far this is what I've come up with that doesn't work, and throws a could not resolve property: datetime of: common.entity.FtpStatus error message: Criteria crit = s.createCriteria(FtpStatus.class); crit = crit

问题 I have a table where the the parent object has an optional many-to-one relationship. The problem is that the table is setup to default the fkey column to 0. When selecting, using fetch="join", etc-- the default of 0 on the fkey is being used to try over and over to select from another table for the ID 0. Of course this doesn't exist, but how can I tell Hibernate to treat a value of 0 to be the same as NULL-- to not cycle through 20+ times in fetching a relationship which doesn't exist? <many

问题 So, this is my first time learning computer language. And I chose python and django. Now, I got many of the basic concepts of python and also django. I can create new page with the views and all other stuff. But I am still confused with the relations, i.e. one to one, many to one, and many to many. Will someone please please please explain it to me. How can I use it? I really need to know. Thanks. 回答1: Especially with django, which makes complicated db design a piece of cake, I think it's

问题 My programm is freezing when I write getters/setters for OneToMany properties. I have these two entities : COMPETENCE_LEVEL @Entity @Table(name="competence_level") public class CompetenceLevel { @Id @GeneratedValue(strategy=GenerationType.AUTO) @Column(name="id_competence_level") private Long idCompetenceLevel; @ManyToOne @JoinColumn(name="id_competence") private Competence competence; @ManyToOne @JoinColumn(name="id_level") private Level level; @ManyToOne @JoinColumn(name="id_profil")

问题 I'm facing LazyInitializationException when I'm trying to access ID of a lazy @ManyToOne reference of a detached entity. I do not want to fetch the refrence completely, but just need the ID (which should be exist in original object in order to fetch refrence in a lazy/deferred manner). EntityA ea = dao.find(1) // find is @Transactional, but transaction is closed after method exits ea.getLazyReference().getId() // here is get exception. lazyReference is a ManyToOne relation and so the foreight

问题 I have two tables with foreign key relations. I've tried searching on how to do it and it always leads to OneToMany & ManyToOne mapping. I have these two tables. user_role user I'm trying to display all the users and show their position by getting the value of the position column to the user_role table. These are my classes User.java @Entity @Table(name="user") public class User { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private long id; .......... private UserRole userRole;

问题 I have two tables with foreign key relations. I've tried searching on how to do it and it always leads to OneToMany & ManyToOne mapping. I have these two tables. user_role user I'm trying to display all the users and show their position by getting the value of the position column to the user_role table. These are my classes User.java @Entity @Table(name="user") public class User { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private long id; .......... private UserRole userRole;

问题 In my auditable entities I have field creationUser which I would like to not update in db on merge operation. Here is my entity code: @Column(updatable=false) @ManyToOne(cascade = CascadeType.MERGE) public User creationUser; But it gives me an error: Unexpected exception PersistenceException: [PersistenceUnit: defaultPersistenceUnit] Unable to build EntityManagerFactory Caused by: org.hibernate.AnnotationException: @Column(s) not allowed on a @ManyToOne property: models.AreaOfMedicine