休眠状态下的模型何时需要可序列化？

Question

I have two model:

@Entity
public class Invoice {

    @Id
    @Column(name="InvoiceID")
    private String InvoiceID;

    @Column(name="Date")
    private Date Date;

    @Column(name="TotalPrice")
    private int TotalPrice;

...
}

    @Entity
    public class Product {

        @Id
        private String ProductID;

        @Column(name="ProductName")
        private String ProductName;

        @Column(name="Quantity")
        private int Quantity;

        @Column(name="Price")
        private int Price;
...
    }

And I have a join model

@Entity
public class InvoiceDetail implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Id
    @ManyToOne
    @JoinColumn(name="InvoiceID")
    private Invoice Invoice;


    @Id
    @ManyToOne
    @JoinColumn(name="ProductID")
    private Product Product;

    ...
}

In InvoiceDetail, if i dont implement Serializable, i will get Caused by: org.hibernate.MappingException: Composite-id class must implement Serializable: com.javainsimpleway.model.InvoiceDetail

But in Invoice and Product model, i dont need to do that. Any one can explain me about that!

Answer 1

The id of an entity must be Serializable . Your String ids in Invoice and Product are both Serializable . Since you are (IMHO mis-)using Invoice as id in InvoiceDetail it also needs to be Serializable