one-to-many

Hibernate unidirectional one to many association - why is a join table better?

由 ぐ巨炮叔叔 提交于 2019-11-27 06:53:55
In this document (scroll down to the Unidirectional section): http://docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#entity-mapping-association-collections it says that a unidirectional one-to-many association with a join table is much preferred to just using a foreign key column in the owned entity. My question is, why is it much preferred? Consider the situation where the owned entity type can also be owned by another parent entity type. Do you put foreign key references in the owned table to both parent tables? What if you have three parent types? It just doesn't scale

PHP/mySQL - how to fetch nested rows into multidimensinal array

由 Deadly 提交于 2019-11-27 06:18:21
问题 Coming from another question of mine where I learnt not to EVER use db queries within loops I consequently have to learn how to fetch all the data in a convenient way before I loop through it. Let's say I have two tables 'scales' and 'items'. Each item in items belongs to one scale in scales and is linked with a foreign key (scaleID). I want to fetch all that data into an array structure in one query such that the first dimension are all the scales with all the columns and nested within, all

@OneToMany without inverse relationship and without a join table?

由 房东的猫 提交于 2019-11-27 05:32:34
问题 This is a similar problem to "Hibernate @OneToMany without a separate join table", in that I need a @OneToMany relationship without a join table. However, I would also like to not define the inverse relationship. Removing the inverse seems to result in a join table being automatically generated... is there a workaround for this? 回答1: In JPA 2.0+ you can use @JoinColumn as a way to avoid to generate joined table. Try it. @OneToMany @JoinColumn(name="COLUMN_NAME") UPDATE The info provided above

deleted object would be re-saved by cascade (remove deleted object from associations)

由 我们两清 提交于 2019-11-27 03:33:33
i have the following two entities: 1- PlayList: @OneToMany(fetch = FetchType.EAGER, mappedBy = "playlist", orphanRemoval = true, cascade = CascadeType.ALL) @OrderBy("adOrder") private Set<PlaylistadMap> PlaylistadMaps = new HashSet<PlaylistadMap>(0); CascadeType.ALL : is needed for save and update on the PlaylistadMap collection when saving or updating the playlist entity. orphanRemoval = true : is needed when deleting the playlist entity, the PlaylistadMap references should be deleteed too. 2- PlaylistadMap: @ManyToOne(fetch = FetchType.EAGER) @JoinColumn(name = "fk_playlist",

Construct JPA query for a OneToMany relation

由 一笑奈何 提交于 2019-11-27 03:31:25
问题 I've those 2 entities Class A { @OneToMany(mappedBy="a") private List<B> bs; } Class B { @ManyToOne private A a; private String name; } 1) I would like to construct a query that says get all A's that have at least one B with name ="mohamede1945" 2) I would like to construct a query that says get all A's that don't have any B with name = "mohamede1945" Could anyone help me? 回答1: You can use the ANY and ALL constructs to filter the subquery. So something like 1. FROM A aEntity WHERE

JPA - Persisting a One to Many relationship

由 孤人 提交于 2019-11-27 03:29:55
Maybe this is a stupid question but it's bugging me. I have a bi-directional one to many relationship of Employee to Vehicles. When I persist an Employee in the database for the first time (i.e. it has no assigned ID) I also want its associated Vehicles to be persisted. This works fine for me at the moment, except that my saved Vehicle entity is not getting the associated Employee mapped automatically, and in the database the employee_id foreign key column in the Vehicle table is null. My question is, is it possible to have the Vehicle's employee persisted at the same time the Employee itself

JPA OneToMany and ManyToOne throw: Repeated column in mapping for entity column (should be mapped with insert=“false” update=“false”)

由 时光毁灭记忆、已成空白 提交于 2019-11-27 03:11:15
I have three classes one of the name is User and this user have other classes instances. Like this; public class User{ @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL) public List<APost> aPosts; @OneToMany(fetch=FetchType.LAZY, cascade = CascadeType.ALL) public List<BPost> bPosts; } public class BPost extends Post { @ManyToOne(fetch=FetchType.LAZY) public User user; } public class APost extends Post { @ManyToOne(fetch=FetchType.LAZY) public User user; } it's working like this but generates emty tables in db. Which have to contains foreign keys. When I tried to use mappedBy and

Hibernate Many to one updating foreign key to null

由 谁说我不能喝 提交于 2019-11-27 02:59:19
问题 I am trying to get my @OneToMany and @ManyToOne relationships correct. Class 1: @Entity public class IdeaProfile { @Id @GeneratedValue private int ideaProfileId; private String name; Date dateConcieved; @OneToOne @JoinColumn(name="statusCode") private Status status; @OneToMany(fetch=FetchType.EAGER, targetEntity=Pitch.class, cascade=CascadeType.ALL) @JoinColumn(name = "ideaProfileId") private List<Pitch> pitchs; ....getters and setters.... Class2: @Entity public class Pitch { @Id

CoreData - one-to-many modeled relationship comes out as one-to-one

由 ε祈祈猫儿з 提交于 2019-11-27 02:42:17
问题 I am new to Core Data modeling, and I am having a hard time understanding how one-to-many relationships work. I have a parent entity called Task , which can have several instances of Comment entity. I modeled it like this: on Comments , a relationship to Task called task with the Task entity a destination. On Task , a relationship called comments , with Comment as its destination, and both relationships are each others inverse. Not defining an inverse results in either warnings or error

Hibernate @OneToMany with mappedBy (parent-child) relationship and cache problem

由 别说谁变了你拦得住时间么 提交于 2019-11-27 01:29:40
问题 I have this problem for a long time now, I have searched the web and SO in and out and didn't find a solution yet. I hope you can help me on that. I have a parent-child relationship between two entities like the following: @Entity public class Parent { // ... @OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.REMOVE) private Set<Child> children = new HashSet<Child>(); // ... } @Entity public class Child { // ... @ManyToOne(fetch = FetchType.LAZY) private Parent
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