JPA中外键兼主键问题：Product关联Document双外键主键识别异常

我来帮你搞定这个问题——你遇到的情况是Eclipse的JPA内容图没把那两个Document外键识别成Product的主键，大概率是因为复合主键的配置细节没做对。下面给你两种标准的实现方案，选一种适配你的代码就行：

先确认Document实体的基础配置 #

首先得保证你的Document和它的主键类DocumentId是合规的，这是后续配置的基础：

Document主键类（DocumentId.java） #

import java.io.Serializable;
import java.util.Objects;

public class DocumentId implements Serializable {
    // 这里的字段要和Document实体的@Id字段完全对应，比如Document用Long类型的id作为主键
    private Long id;

    // 必须有无参构造器
    public DocumentId() {}

    public DocumentId(Long id) {
        this.id = id;
    }

    // 必须重写equals和hashCode，JPA依赖这个判断主键唯一性
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        DocumentId that = (DocumentId) o;
        return Objects.equals(id, that.id);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id);
    }

    // getter和setter方法
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
}

Document实体类 #

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.Table;

@Table(name = "DOCUMENT")
@Entity
@IdClass(DocumentId.class)
public class Document {
    @Id
    private Long id;
    // 你的其他业务属性...

    // getter和setter方法
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
}

方案一：用@IdClass实现Product的复合主键 #

这种方式适合想把主键字段和实体关联分开定义的场景：

Product主键类（ProductId.java） #

import java.io.Serializable;
import java.util.Objects;

public class ProductId implements Serializable {
    // 字段名要遵循「关联属性名+Document主键字段名」的规则，比如关联属性是doc1，Document主键是id，这里就叫doc1Id
    private Long doc1Id;
    private Long doc2Id;

    public ProductId() {}

    public ProductId(Long doc1Id, Long doc2Id) {
        this.doc1Id = doc1Id;
        this.doc2Id = doc2Id;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ProductId productId = (ProductId) o;
        return Objects.equals(doc1Id, productId.doc1Id) && Objects.equals(doc2Id, productId.doc2Id);
    }

    @Override
    public int hashCode() {
        return Objects.hash(doc1Id, doc2Id);
    }

    // getter和setter方法
    public Long getDoc1Id() { return doc1Id; }
    public void setDoc1Id(Long doc1Id) { this.doc1Id = doc1Id; }
    public Long getDoc2Id() { return doc2Id; }
    public void setDoc2Id(Long doc2Id) { this.doc2Id = doc2Id; }
}

Product实体类 #

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Table(name = "PRODUCT")
@Entity
@IdClass(ProductId.class)
public class Product {
    // 关键：同时用@Id和@ManyToOne，把这个关联字段标记为主键+外键
    @Id
    @ManyToOne
    @JoinColumn(name = "DOC1_ID", referencedColumnName = "ID")
    private Document doc1;

    @Id
    @ManyToOne
    @JoinColumn(name = "DOC2_ID", referencedColumnName = "ID")
    private Document doc2;

    // 你的其他业务属性...

    // getter和setter方法
    public Document getDoc1() { return doc1; }
    public void setDoc1(Document doc1) { this.doc1 = doc1; }
    public Document getDoc2() { return doc2; }
    public void setDoc2(Document doc2) { this.doc2 = doc2; }
}

方案二：用@EmbeddedId实现Product的复合主键 #

这种方式更直观，把复合主键做成一个可嵌入的组件，适合逻辑上把两个外键当成一个整体主键的场景：

Product嵌入主键类（ProductEmbeddedId.java） #

import java.io.Serializable;
import java.util.Objects;
import javax.persistence.Embeddable;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;

@Embeddable
public class ProductEmbeddedId implements Serializable {
    @ManyToOne
    @JoinColumn(name = "DOC1_ID", referencedColumnName = "ID")
    private Document doc1;

    @ManyToOne
    @JoinColumn(name = "DOC2_ID", referencedColumnName = "ID")
    private Document doc2;

    public ProductEmbeddedId() {}

    public ProductEmbeddedId(Document doc1, Document doc2) {
        this.doc1 = doc1;
        this.doc2 = doc2;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ProductEmbeddedId that = (ProductEmbeddedId) o;
        return Objects.equals(doc1, that.doc1) && Objects.equals(doc2, that.doc2);
    }

    @Override
    public int hashCode() {
        return Objects.hash(doc1, doc2);
    }

    // getter和setter方法
    public Document getDoc1() { return doc1; }
    public void setDoc1(Document doc1) { this.doc1 = doc1; }
    public Document getDoc2() { return doc2; }
    public void setDoc2(Document doc2) { this.doc2 = doc2; }
}

Product实体类 #

import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.Table;

@Table(name = "PRODUCT")
@Entity
public class Product {
    @EmbeddedId
    private ProductEmbeddedId id;

    // 你的其他业务属性...

    // getter和setter方法
    public ProductEmbeddedId getId() { return id; }
    public void setId(ProductEmbeddedId id) { this.id = id; }
}

最后一步：让Eclipse识别配置 #

配置完之后，右键你的JPA项目，选择JPA -> Synchronize JPA Entities，刷新一下JPA内容图，这时候那两个外键应该就能被正确识别成Product的主键了。

内容的提问来源于stack exchange，提问作者Wesley Rosa