JPA复合主键使用

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本文介绍了如何在JPA中实现复合主键，通过@EmbeddedId和@IdClass两种方式详细解析了复合主键类的创建和使用。并强调了主键类必须实现序列化、拥有公共无参构造方法以及equals()和hashCode()方法。同时，展示了在实体类中如何获取复合主键的各个部分。

数据库表

create table RENT_CERT_VENDOR_TYPE ( CERT_TYPE_ID NUMBER not null, VENDOR_ID NUMBER not null, CERT_TYPE_VENDOR_ID NUMBER not null ) ; alter table RENT_CERT_VENDOR_TYPE add constraint PK_RENT_CERT_VENDOR_TYPE primary key (CERT_TYPE_ID, VENDOR_ID); alter table RENT_CERT_VENDOR_TYPE add constraint FK_CERT_VENDOR_CERT_TYPE_ID foreign key (CERT_TYPE_ID) references RENT_CERT_TYPE (ID); alter table RENT_CERT_VENDOR_TYPE add constraint FK_CERT_VENDOR_VENDOR_ID foreign key (VENDOR_ID) references RENT_VENDOR (ID);

一、使用@EmbeddedId

eclipse生成的复合主键类

@Embeddable public class RentCertVendorTypePK implements Serializable { //default serial version id, required for serializable classes. private static final long serialVersionUID = 1L; @Column(name="CERT_TYPE_ID") private long certTypeId; @Column(name="VENDOR_ID") private long vendorId; public RentCertVendorTypePK() { } public long getCertTypeId() { return this.certTypeId; } public void setCertTypeId(long certTypeId) { this.certTypeId = certTypeId; } public long getVendorId() { return this.vendorId; } public void setVendorId(long vendorId) { this.vendorId = vendorId; } public boolean equals(Object other) { if (this == other) { return true; } if (!(other instanceof RentCertVendorTypePK)) { return false; } RentCertVendorTypePK castOther = (RentCertVendorTypePK)other; return (this.certTypeId == castOther.certTypeId) && (this.vendorId == castOther.vendorId); } public int hashCode() { final int prime = 31; int hash = 17; hash = hash * prime + ((int) (this.certTypeId ^ (this.certTypeId >>> 32))); hash = hash * prime + ((int) (this.vendorId ^ (this.vendorId >>> 32))); return hash; } }

主键类必需满足下列条件：
(1)必需被序列化
(2)必需有一个公共的无参构造方法
(3)必需实现equals()和hashCode()方法

使用主键类

@Entity @Table(name="RENT_CERT_VENDOR_TYPE") public class RentCertVendorType implements Serializable { private static final long serialVersionUID = 1L; @EmbeddedId private RentCertVendorTypePK id; @Column(name="CERT_TYPE_VENDOR_ID") private BigDecimal certTypeVendorId; //bi-directional many-to-one association to RentCertType @ManyToOne @JoinColumn(name="CERT_TYPE_ID") private RentCertType rentCertType; public RentCertVendorType() { } public RentCertVendorTypePK getId() { return this.id; } public void setId(RentCertVendorTypePK id) { this.id = id; } public BigDecimal getCertTypeVendorId() { return this.certTypeVendorId; } public void setCertTypeVendorId(BigDecimal certTypeVendorId) { this.certTypeVendorId = certTypeVendorId; } public RentCertType getRentCertType() { return this.rentCertType; } public void setRentCertType(RentCertType rentCertType) { this.rentCertType = rentCertType; } }

使用eclipse生成JPA实体的向导界面中，复合主键类的key generator指定为auto，则插件会自动识别数据库表中的复合主键，并生成复合主键类。

这种方法在Entity中获取复合主键中的某列属性如VENDOR_ID时，需要rentCertVendorType.getRentCertVendorTypePK().getVendorId()，其中rentCertVendorType为RentCertVendorType类对象。

二、使用@IdClass

主键类

public class RentCertVendorTypePK implements Serializable { //default serial version id, required for serializable classes. private static final long serialVersionUID = 1L; private long certTypeId; private long vendorId; public RentCertVendorTypePK() { } public long getCertTypeId() { return this.certTypeId; } public void setCertTypeId(long certTypeId) { this.certTypeId = certTypeId; } public long getVendorId() { return this.vendorId; } public void setVendorId(long vendorId) { this.vendorId = vendorId; } public boolean equals(Object other) { if (this == other) { return true; } if (!(other instanceof RentCertVendorTypePK)) { return false; } RentCertVendorTypePK castOther = (RentCertVendorTypePK)other; return (this.certTypeId == castOther.certTypeId) && (this.vendorId == castOther.vendorId); } public int hashCode() { final int prime = 31; int hash = 17; hash = hash * prime + ((int) (this.certTypeId ^ (this.certTypeId >>> 32))); hash = hash * prime + ((int) (this.vendorId ^ (this.vendorId >>> 32))); return hash; } }

Entity

@IdClass(RentCertVendorTypePK.class) @Entity @Table(name="RENT_CERT_VENDOR_TYPE") public class RentCertVendorType implements Serializable { private static final long serialVersionUID = 1L; @Id @Column(name="CERT_TYPE_ID") private long certTypeId; @Id @Column(name="VENDOR_ID") private long vendorId; @Column(name="CERT_TYPE_VENDOR_ID") private BigDecimal certTypeVendorId; //bi-directional many-to-one association to RentCertType @ManyToOne @JoinColumn(name="CERT_TYPE_ID") private RentCertType rentCertType; public RentCertVendorType() { } public RentCertVendorTypePK getId() { return this.id; } public void setId(RentCertVendorTypePK id) { this.id = id; } public BigDecimal getCertTypeVendorId() { return this.certTypeVendorId; } public void setCertTypeVendorId(BigDecimal certTypeVendorId) { this.certTypeVendorId = certTypeVendorId; } public RentCertType getRentCertType() { return this.rentCertType; } public void setRentCertType(RentCertType rentCertType) { this.rentCertType = rentCertType; } }

这种方法在Entity中获取复合主键中的某列属性如VENDOR_ID时，只需要rentCertVendorType.getVendorId()，其中rentCertVendorType为RentCertVendorType类对象。