JPA - 使用复合PK和FK并定义关系 [英] JPA - Using composite PK's and FK's and defining relationships

问题描述

  @ javax.persistence.Entity 
 public class Book {
 @ javax.persistence.EmbeddedId 
私人BookPK ID; 
 
私有字符串标题; 
 
 @ javax.persistence.ManyToOne（fetch = javax.persistence.FetchType.LAZY）
 @ javax.persistence.JoinColumns（{
 @ javax.persistence.JoinColumn（name = LNGCOD，referencedColumnName =LNGCOD），
 @ javax.persistence.JoinColumn（name =LIBCOD，referencedColumnName =LIBCOD）}）
 private语言语言; 
 
 
 @ javax.persistence.Entity 
 public class Language {
 @ javax.persistence.EmbeddedId 
 private LanguagePK id; 
 
私人字符串名称; 
} 
  

带有组成的PK：

  @Embeddable 
公共类BookPK实现Serializable {
私有Integer bookcod; 
 private Integer libcod; 
} 
 
 @Embeddable 
 public class LanguagePK实现Serializable {
 private Integer lngcod; 
 private Integer libcod; 
 
 
 
 $ b如果我尝试创建一个新书并坚持它，我会得到一个异常告诉我libcod在插入语句中发现两次（Column'libcod'指定两次）。但是，在定义JoinColumn时，我不能使用insertable = false（在属性中混合插入和不可插入列是不允许的）。 
 
 
有没有方法来定义这些对象+关系，这样列由Hibernate自动管理？ （我特别想到libcod）。
 
 
 
谢谢。   
解决方案
创建第三个属性Integer libcod;在书上。让该属性管理libcod的db状态。对连接语言中的两个属性使用insertable = false，updatable = false。在你的setLanguage中设置private libcod = language.libcod。不要为私有libcod公开一个getter / setter。
 
 
 
是否在插入时生成任何值？这可能会使事情进一步复杂化，我想。
 
I got these 2 entities:
@javax.persistence.Entity
public class Book {
    @javax.persistence.EmbeddedId
    private BookPK id;

    private String title;

    @javax.persistence.ManyToOne(fetch = javax.persistence.FetchType.LAZY)
    @javax.persistence.JoinColumns({ 
            @javax.persistence.JoinColumn(name = "LNGCOD", referencedColumnName = "LNGCOD"),
            @javax.persistence.JoinColumn(name = "LIBCOD", referencedColumnName = "LIBCOD") })
    private Language language;
}

@javax.persistence.Entity
public class Language {
    @javax.persistence.EmbeddedId
    private LanguagePK id;

    private String name;
}
with composed PK's:
@Embeddable
public class BookPK implements Serializable {
    private Integer bookcod;
    private Integer libcod;
}

@Embeddable
public class LanguagePK implements Serializable {
    private Integer lngcod;
    private Integer libcod;
}
If I try to create a new Book and persist it, I get an exception telling me libcod is found twice in the insert statement ("Column 'libcod' specified twice"). But I can't use "insertable = false" when defining the JoinColumn ("Mixing insertable and non insertable columns in a property is not allowed").

Is there any way to define these objects + relationship so the columns are managed automatically by Hibernate ? (I am especially thinking of libcod).

Thank you.
解决方案
Create a third property "Integer libcod;" on the Book.  Have that property manage the db state of libcod.  Use insertable=false,updatable=false for both properties in the join to Language.  in your "setLanguage" set the private libcod = language.libcod.  don't expose a getter/setter for the private libcod.

Are any of the values generated at insert time?  This could complicate things further, I suppose.

                        
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