Java 将主键作为外键映射到另一个表

Mapping of primary key as foreign key to another table

提问by nkr

I have a problem regarding a foreign key relationship and its JPA counterpart.

我有一个关于外键关系及其 JPA 对应关系的问题。

In the following tables. means_of_transportis a table with a consecutive numbering. The other tables have less entries with a mapping of their primary key as a foreign key to the primary key of means_of_transport. Sadly, I cannot change the data model.

在下表中。means_of_transport是一个连续编号的表格。其他表的条目较少，它们的主键作为外键映射到 的主键means_of_transport。遗憾的是，我无法更改数据模型。

Table means_of_transport

桌子 means_of_transport

CREATE TABLE means_of_transport (
    id INT PRIMARY KEY NOT NULL,
    max_capacity INT
);

Table ocean_ship

桌子 ocean_ship

CREATE TABLE ocean_ship (
    means_of_transport_id INT PRIMARY KEY NOT NULL,
    name VARCHAR(45) NOT NULL,
    FOREIGN KEY ( means_of_transport_id ) REFERENCES means_of_transport ( id )
);
CREATE INDEX fk_ship_means_of_transport1_idx ON ocean_ship ( means_of_transport_id );

There are more tables besides ocean_shipwith the same key structure but other fields.

除了ocean_ship具有相同键结构但其他字段之外，还有更多表。

MeansOfTransport.java

MeansOfTransport.java

@Entity
@Table(name = "means_of_transport")
public class MeansOfTransport extends Model {
    @Id
    public Integer id;
    public Integer maxCapacity;
}

OceanShip.java

海洋之船.java

@Entity
@Table(name = "ocean_ship")
public class OceanShip extends Model {
    @Id
    @OneToOne
    @JoinColumn(table = "means_of_transport", referencedColumnName = "id")
    public MeansOfTransport meansOfTransport;

    public String name;
}

Now every time I try to use OceanShipin another JPA class as a field, I get this error: Error reading annotations for models.Classname.

现在，每次我尝试OceanShip在另一个 JPA 类中将其用作字段时，都会收到此错误：Error reading annotations for models.Classname.

Am I missing some annotations?

我是否缺少一些注释？

edit

编辑

Example usage:

用法示例：

@ManyToOne
@Column(name = "ocean_ship")
public OceanShip oceanShip;

Full stack trace:

完整的堆栈跟踪：

play.api.UnexpectedException: Unexpected exception[RuntimeException: Error reading annotations for models.ContainerOrder]
        at play.core.ReloadableApplication$$anonfun$get$$anonfun$apply$$anonfun.apply(ApplicationProvider.scala:150) ~[play_2.10.jar:2.1.5]
        at play.core.ReloadableApplication$$anonfun$get$$anonfun$apply$$anonfun.apply(ApplicationProvider.scala:114) ~[play_2.10.jar:2.1.5]
        at scala.Option.map(Option.scala:145) ~[scala-library.jar:na]
        at play.core.ReloadableApplication$$anonfun$get$$anonfun$apply.apply(ApplicationProvider.scala:114) ~[play_2.10.jar:2.1.5]
        at play.core.ReloadableApplication$$anonfun$get$$anonfun$apply.apply(ApplicationProvider.scala:112) ~[play_2.10.jar:2.1.5]
        at scala.util.Either$RightProjection.flatMap(Either.scala:523) ~[scala-library.jar:na]
Caused by: java.lang.RuntimeException: Error reading annotations for models.ContainerOrder
        at com.avaje.ebeaninternal.server.deploy.parse.ReadAnnotations.readAssociations(ReadAnnotations.java:54) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.BeanDescriptorManager.readDeployAssociations(BeanDescriptorManager.java:1034) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.BeanDescriptorManager.readEntityDeploymentAssociations(BeanDescriptorManager.java:565) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.BeanDescriptorManager.deploy(BeanDescriptorManager.java:252) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.core.InternalConfiguration.<init>(InternalConfiguration.java:124) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.core.DefaultServerFactory.createServer(DefaultServerFactory.java:210) ~[avaje-ebeanorm-server.jar:na]
Caused by: java.lang.NullPointerException: null
        at com.avaje.ebeaninternal.server.deploy.BeanTable.createJoinColumn(BeanTable.java:94) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.parse.AnnotationAssocOnes.readAssocOne(AnnotationAssocOnes.java:145) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.parse.AnnotationAssocOnes.parse(AnnotationAssocOnes.java:54) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.parse.ReadAnnotations.readAssociations(ReadAnnotations.java:45) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.BeanDescriptorManager.readDeployAssociations(BeanDescriptorManager.java:1034) ~[avaje-ebeanorm-server.jar:na]
        at com.avaje.ebeaninternal.server.deploy.BeanDescriptorManager.readEntityDeploymentAssociations(BeanDescriptorManager.java:565) ~[avaje-ebeanorm-server.jar:na]

采纳答案by nkr

The error message came up because some annotations were wrong.

出现错误消息是因为某些注释是错误的。

I changed the primary key of OceanShipfrom MeansOfTransportto Integerand have now to be careful what I enter there. That's the price I have to pay.

我将OceanShipfrom的主键更改为MeansOfTransportto Integer，现在必须小心我在那里输入的内容。这是我必须付出的代价。

Additionally I changed the annotation where I use OceanShipfrom this

另外，我OceanShip从这里更改了我使用的注释

@ManyToOne
@Column(name = "ocean_ship")
public OceanShip oceanShip;

to this

对此

@ManyToOne
@JoinColumn(name = "ocean_ship", referencedColumnName = "means_of_transport_id")
public OceanShip oceanCarrierShip;

回答by peter.petrov

I think your DB model is conceptually not right.

我认为您的数据库模型在概念上是不正确的。

It should be something like this below.

下面应该是这样的。

The ocean_ship_id is the PK of the ocean_ship table. And means_of_transport_id from ocean_ship is just a FK to the "base" table means_of_transport.

Ocean_ship_id 是 Ocean_ship 表的 PK。而来自ocean_ship 的means_of_transport_id 只是“基本”表means_of_transport 的FK。

So I would say you get your DB model right, then worry about the JPA mapping.

所以我会说你的数据库模型是正确的，然后担心 JPA 映射。

CREATE TABLE ocean_ship (
    ocean_ship_id INT PRIMARY KEY NOT NULL,
    means_of_transport_id INT NOT NULL,
    name VARCHAR(45) NOT NULL,
    FOREIGN KEY ( means_of_transport_id ) REFERENCES means_of_transport ( id )
);

回答by peter.petrov

See @PrimaryKeyJoinColumnand the ideas given in this thread.

请参阅@PrimaryKeyJoinColumn此线程中给出的想法。

Shared primary key with JPA @MapsId annotation

使用 JPA @MapsId 注释共享主键

Might be helpful maybe?

可能有帮助吗？