JPA OneToMany使用来自不同表的列

huangapple
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英文:

JPA OneToMany using columns from different tables

问题

以下是您提供的内容的翻译部分：

我在我的关系型数据库中有以下表格。

制造商表：

  1. CREATE TABLE manufacturer (
  2.   id int(10) unsigned NOT NULL AUTO_INCREMENT,
  3.   name varchar(100),
  4.   code varchar(50)
  5. );

产品表：

  1. CREATE TABLE product (
  2.   id int(10) unsigned NOT NULL AUTO_INCREMENT,
  3.   manufacturer_id int(10),
  4.   name varchar(100),
  5.   revision_id int(10),
  6.   CONSTRAINT product_man_fk FOREIGN KEY (manufacturer_id) REFERENCES manufacturer (id) ON DELETE CASCADE
  7. );

修订表：

  1. CREATE TABLE revision (
  2.   id int(10),
  3.   code varchar(50),
  4.   CONSTRAINT revision_uq UNIQUE(id, code)
  5. );

请注意，在“revision”表中，“id”不是主键（PK）也不是唯一列，只有“id”和“code”的组合是唯一的。

现在，就JPA而言，我需要在“Product”类中只有一个“Revision”（而不是它们的集合），并且我需要进行如下映射：

  1. class Product {
  2. ...
  3.     @ManyToOne
  4.     @JoinColumn(name="manufacturer_id")
  5.     private Manufacturer manufacturer;
  7.     @ManyToOne
  8.     @JoinColumns({
  9.       @JoinColumn(name="revision_id", referencedColumnName="id"),
  10.       @JoinColumn(name="manufacturer.code", referencedColumnName="code")
  11.     })
  12.     private Revision revision;
  13. }

显然，这不起作用，因为“manufacturer.code”不是“product”表的列。是否有任何方法可以将另一个父实体的字段传递给不同的“@ManyToOne”注解以进行映射？

提前感谢。

英文:

I have the following tables in my relational DB.

  1.  CREATE TABLE manufacturer (
  2.   id int(10) unsigned NOT NULL AUTO_INCREMENT,
  3.   name varchar(100),
  4.   code varchar(50)
  5. );
  1.  CREATE TABLE product (
  2.   id int(10) unsigned NOT NULL AUTO_INCREMENT,
  3.   manufacturer_id int(10)
  4.   name varchar(100),
  5.   revision_id int(10)
  6.   CONSTRAINT product_man_fk FOREIGN KEY (manufacturer_id) REFERENCES manufacturer (id) ON DELETE CASCADE
  7. );
  1.  CREATE TABLE revision (
  2.   id int(10),
  3.   code varchar(50),
  4.   CONSTRAINT revision_uq UNIQUE(id, code)
  5. );

Please note that id is not a PK nor a unique column in revision, only a combination of id and code is unique.

Now, in terms of JPA, I need to have only one Revision within the class Product (not a collection of them) and I need to map it as follows:

  1. class Product {
  2. ...
  3.     @ManyToOne
  4.     @JoinColumn(name="manufacturer_id")
  5.     private Manufacturer manufacturer;
  7.     @ManyToOne
  8.     @JoinColumns({
  9.       @JoinColumn(name="revision_id", referencedColumnName="id"),
  10.       @JoinColumn(name="manufacturer.code", referencedColumnName="code")
  11.     })
  12.     private Revision revision;
  13. }

This doesn't work obviously, as manufacturer.code is not a column of table product.
Is there any way to somehow pass a field from another parent entity to a different @ManyToOne annotation for mapping?

Thanks in advance

答案1

得分: 1

在JPA中，你不能直接从一个实体引用另一个实体的关系映射注解中的字段。但是，你可以通过引入一个额外的映射实体来实现所需的映射。

  1. 创建一个新的映射实体（例如ProductRevisionMapping），表示Product和Revision之间的映射关系。这个实体将具有由product_id（对Product的外键）和revision_id（对Revision的外键）组成的复合主键。
  1. @Entity
  2. @Table(name = "product_revision_mapping")
  3. public class ProductRevisionMapping implements Serializable {
  5.     @Id
  6.     @ManyToOne
  7.     @JoinColumn(name = "product_id")
  8.     private Product product;
  10.     @Id
  11.     @ManyToOne
  12.     @JoinColumns({
  13.         @JoinColumn(name = "revision_id", referencedColumnName = "id"),
  14.         @JoinColumn(name = "revision_code", referencedColumnName = "code")
  15.     })
  16.     private Revision revision;
  17. }
  1. 修改Product实体，使其与ProductRevisionMapping具有一对一的映射关系。
  1. @Entity
  2. @Table(name = "product")
  3. public class Product {
  5.     // ...
  7.     @OneToOne(mappedBy = "product")
  8.     private ProductRevisionMapping productRevisionMapping;
  11.     public Revision getRevision() {
  12.         if (productRevisionMapping != null) {
  13.             return productRevisionMapping.getRevision();
  14.         }
  15.         return null;
  16.     }
  18.     public void setRevision(Revision revision) {
  19.         if (productRevisionMapping == null) {
  20.             productRevisionMapping = new ProductRevisionMapping();
  21.             productRevisionMapping.setProduct(this);
  22.         }
  23.         productRevisionMapping.setRevision(revision);
  24.     }
  25. }

通过这种修改，你可以在Product和Revision之间建立一对一的关系，使用ProductRevisionMapping作为中介映射实体。

确保适当处理Product和Revision实体的保存和更新，以维护映射的一致性。

英文:

In JPA, you cannot directly reference a field from one entity to another entity's relationship mapping annotation. However, you can achieve the desired mapping by introducing an additional mapping entity.

  1. Create a new mapping entity (e.g. ProductRevisionMapping), which represents the mapping between Product and Revision. This entity will have a composite primary key consisting of product_id (foreign key to Product) and revision_id (foreign key to Revision).
  1. @Entity
  2. @Table(name = "product_revision_mapping")
  3. public class ProductRevisionMapping implements Serializable {
  5.     @Id
  6.     @ManyToOne
  7.     @JoinColumn(name = "product_id")
  8.     private Product product;
  10.     @Id
  11.     @ManyToOne
  12.     @JoinColumns({
  13.         @JoinColumn(name = "revision_id", referencedColumnName = "id"),
  14.         @JoinColumn(name = "revision_code", referencedColumnName = "code")
  15.     })
  16.     private Revision revision;
  17. }
  1. Modify the Product entity to have a one-to-one mapping with ProductRevisionMapping.
  1. @Entity
  2. @Table(name = "product")
  3. public class Product {
  5.     // ...
  7.     @OneToOne(mappedBy = "product")
  8.     private ProductRevisionMapping productRevisionMapping;
  11.     public Revision getRevision() {
  12.         if (productRevisionMapping != null) {
  13.             return productRevisionMapping.getRevision();
  14.         }
  15.         return null;
  16.     }
  18.     public void setRevision(Revision revision) {
  19.         if (productRevisionMapping == null) {
  20.             productRevisionMapping = new ProductRevisionMapping();
  21.             productRevisionMapping.setProduct(this);
  22.         }
  23.         productRevisionMapping.setRevision(revision);
  24.     }
  25. }

With this modification, you can have a one-to-one relationship between Product and Revision, using the ProductRevisionMapping as an intermediary mapping entity.

> Make sure to handle the saving and updating of Product and Revision entities appropriately to maintain the consistency of the mapping.

huangapple
  • 本文由 发表于 2023年6月2日 03:22:59
  • 转载请务必保留本文链接：https://go.coder-hub.com/76385078.html
  • hibernate
  • java
  • jpa
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