联合主键

一：背景介绍

在很多项目中，一个数据库表不仅仅只有一个约束条件，所以需要设置多个主键，来构成约束。但是在同时对多个主键进行增删改查的操作后，就难以下手了，所以需要引入联合主键的概念，将多个主键糅合归纳到一个主键中，从而方便相关操作的实行。

二：具体操作

不多说，直接先看数据库的结构：

表的字段值：

其主键为：

在hibernate下，我们主要来看一下实体bean的配置，其他的具体CRUD操作此处不做编写：

实体TpsControl类代码如下：
package yspos.boss.urm.entity;

import java.io.Serializable;

import javax.persistence.AttributeOverride;
import javax.persistence.AttributeOverrides;
import javax.persistence.Column;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * Cmmtinorg entity. 
 */

@Entity    -----------注解
@Table(name = "TPS_CONTROL") ------------------对应的表名称
public class TpsControl implements Serializable { --1.必须实现Serializable

    
    private static final long serialVersionUID = -202989070727685638L;
    
    private TpsControlId id;  ----------联合主键，可以映射到实体类TpsControlId
    private String ifControl;
    private Integer concurrentNumber;
    private Integer monthVisit;
    private String reqIp;
    private String remark;
    private Integer accNameLimit;
    
    
    public TpsControl() { ------必须有默认的 public无参数的构造方法
    }

    public TpsControl(TpsControlId id) {
        this.id = id;
    }

    public TpsControl(TpsControlId id,String ifControl, Integer concurrentNumber, Integer monthVisit,
            String reqIp, String remark, Integer accNameLimit) {
        this.id = id;
        this.ifControl = ifControl;
        this.concurrentNumber = concurrentNumber;
        this.monthVisit = monthVisit;
        this.reqIp = reqIp;
        this.remark = remark;
        this.accNameLimit = accNameLimit;
    }

    @EmbeddedId                      ---将嵌入式主键类使用 @Embeddable 标注，表示这个是一个嵌入式类
    @AttributeOverrides( {           ----------------@AttributeOverrides 属性映射
        @AttributeOverride(name = "src", column = @Column(name = "SRC", nullable = false, length = 5)),
        @AttributeOverride(name = "msgCode", column = @Column(name = "MSG_CODE", nullable = false, length = 20)),
        @AttributeOverride(name = "method", column = @Column(name = "METHOD", nullable = false, length = 30)) })
    public TpsControlId getId() {
        return id;
    }
    
    public void setId(TpsControlId id) {
        this.id = id;
    }

    @Column(name = "IF_CONTROL", length = 1)    -------对应于表字段的信息
    public String getIfControl() {
        return ifControl;
    }


    public void setIfControl(String ifControl) {
        this.ifControl = ifControl;
    }

    @Column(name = "CONCURRENT_NUMBER",  length = 10)
    public Integer getConcurrentNumber() {
        return concurrentNumber;
    }


    public void setConcurrentNumber(Integer concurrentNumber) {
        this.concurrentNumber = concurrentNumber;
    }

    @Column(name = "MONTH_VISIT", length = 20)
    public Integer getMonthVisit() {
        return monthVisit;
    }


    public void setMonthVisit(Integer monthVisit) {
        this.monthVisit = monthVisit;
    }

    @Column(name = "REQ_IP", length = 100)
    public String getReqIp() {
        return reqIp;
    }


    public void setReqIp(String reqIp) {
        this.reqIp = reqIp;
    }

    @Column(name = "REMARK", length = 100)
    public String getremark() {
        return remark;
    }


    public void setremark(String remark) {
        this.remark = remark;
    }

    @Column(name = "ACC_NAME_LIMIT", length = 10)
    public Integer getAccNameLimit() {
        return accNameLimit;
    }


    public void setAccNameLimit(Integer accNameLimit) {
        this.accNameLimit = accNameLimit;
    }
}

联合主键类：

实体TpsControlId类如下：
package yspos.boss.urm.entity;

import javax.persistence.Column;

import yspos.boss.cmmt.entity.CmmtcityId;

public class TpsControlId implements java.io.Serializable {
    private static final long serialVersionUID = 2719054247718051949L;
    
    private String src;
    private String msgCode;
    private String method;
    
    
    public TpsControlId() {
    }


    public TpsControlId(String src, String msgCode, String method) {
        super();
        this.src = src;
        this.msgCode = msgCode;
        this.method = method;
    }


    @Column(name = "SRC", nullable = false, length = 5)
    public String getSrc() {
        return src;
    }


    public void setSrc(String src) {
        this.src = src;
    }


    @Column(name = "MSG_CODE", nullable = false, length = 20)
    public String getMsgCode() {
        return msgCode;
    }


    public void setMsgCode(String msgCode) {
        this.msgCode = msgCode;
    }


    @Column(name = "METHOD", nullable = false, length = 30)
    public String getMethod() {
        return method;
    }


    public void setMethod(String method) {
        this.method = method;
    }
    
    
    public boolean equals(Object other) {      ---必须覆盖 equals和 hashCode 方法
        if ((this == other))
            return true;
        if ((other == null))
            return false;
        if (!(other instanceof TpsControlId))
            return false;
        TpsControlId castOther = (TpsControlId) other;

        return ((this.getSrc() == castOther.getSrc()) || (this
                .getSrc() != null
                && castOther.getSrc() != null && this.getSrc().equals(
                castOther.getSrc())))
                && ((this.getMsgCode() == castOther.getMsgCode()) || (this
                        .getMsgCode() != null
                        && castOther.getMsgCode() != null && this.getMsgCode()
                        .equals(castOther.getMsgCode())))
                && ((this.getMethod() == castOther.getMethod()) || (this
                        .getMethod() != null
                        && castOther.getMethod() != null && this.getMethod()
                        .equals(castOther.getMethod())));
    }
    
    public int hashCode() {
        int result = 17;

        result = 37 * result
                + (getSrc() == null ? 0 : this.getSrc().hashCode());
        result = 37 * result
                + (getMsgCode() == null ? 0 : this.getMsgCode().hashCode());
        result = 37 * result
                + (getMethod() == null ? 0 : this.getMethod().hashCode());
        return result;
    }

}

符合条件： 

*         1.必须实现Serializable

 *        2.必须有默认的 public无参数的构造方法、必须覆盖 equals和 hashCode 方法，这些要求与使用复合主键的要求相同

 *        3.将嵌入式主键类使用 @Embeddable 标注，表示这个是一个嵌入式类。

 

--->如果要求一个类要去实现Serializable，往往表示这个类的实例要进行网络传输，从A系统传到B系统，以字节形式传输，到达B后再把这些字节恢复成对象；

--->equals和hashCode两个方法常用哈希算法相关，比如要把对象放入TreeSet容器里，就需要容器里元素对应的类要重写equals和hashCode方法，因为TreeSet背后使用了哈希算法和哈希表。