数据库投射只@OneToMany的两个区别

分类: IT文章 • 2024-08-17 17:50:01

数据库映射只@OneToMany的两个区别

========================== (不加referencedColumnName的时候) ==================

@JoinColumn(name="dividend_id")的情况

@Entity
@Table(name="wxsc_order")
public class Order extends EntitySupport {
	
	private static final long serialVersionUID = 1L;
	
	@Column(name="order_id")
	private String orderId;//订单号
	
	@OneToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)//让Dividend去维护外键关系
	@JoinColumn(name="dividend_id")
	private Dividend dividend;//赠品

@Entity()
@Table(name="wxsc_dividend")
public class Dividend extends EntitySupport {
	
	private static final long serialVersionUID = 1L;

	@Column(name="dividend_id")
	private String dividendId;//赠品ID
	
	@Column(name="dividend_name")
	private String dividendName;//赠品名称
	
	@Column(name="dividend_number")
	private String dividendNumber;//赠品编号
	
	private String attribute;//赠品属性
	
	private int quantity;//数量

	@OneToOne(cascade=CascadeType.ALL,fetch=FetchType.LAZY,mappedBy="dividend")//让这个外键生成到order表当中。
	@JoinColumn(name="order_id")
	private Order order;

其映射的关系如下：


mysql> show create table wxsc_dividend;
+---------------+---------------------------------------------------------------------------------------------------------------
| Table         | Create Table
+---------------+---------------------------------------------------------------------------------------------------------------
| wxsc_dividend | CREATE TABLE `wxsc_dividend` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `createTime` datetime NOT NULL,
  `updateTime` datetime NOT NULL,
  `version` int(11) NOT NULL,
  `attribute` varchar(255) DEFAULT NULL,
  `dividend_id` varchar(255) DEFAULT NULL,
  `dividend_name` varchar(255) DEFAULT NULL,
  `dividend_number` varchar(255) DEFAULT NULL,
  `quantity` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8


mysql> show create table wxsc_dividend;
+---------------+---------------------------------------------------------------------------------------------------------------
| Table         | Create Table
+---------------+---------------------------------------------------------------------------------------------------------------
| wxsc_dividend | CREATE TABLE `wxsc_dividend` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `createTime` datetime NOT NULL,
  `updateTime` datetime NOT NULL,
  `version` int(11) NOT NULL,
  `attribute` varchar(255) DEFAULT NULL,
  `dividend_id` varchar(255) DEFAULT NULL,
  `dividend_name` varchar(255) DEFAULT NULL,
  `dividend_number` varchar(255) DEFAULT NULL,
  `quantity` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8






加了referencedColumnName之后
@JoinColumn(name="dividend_id",referencedColumnName="dividendId")
的情况





@Entity
@Table(name="wxsc_order")
public class Order extends EntitySupport {
	
	private static final long serialVersionUID = 1L;

	@Column(name="order_id")
	private String orderId;//订单号
	
	@OneToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)//让Dividend去维护外键关系
	@JoinColumn(name="dividend_id",referencedColumnName="dividend_id")
	private Dividend dividend;//赠品






@Entity()
@Table(name="wxsc_dividend")
public class Dividend extends EntitySupport {
	
	private static final long serialVersionUID = 1L;

	@Column(name="dividend_id")
	private String dividendId;//赠品ID
	
	@Column(name="dividend_name")
	private String dividendName;//赠品名称
	
	@Column(name="dividend_number")
	private String dividendNumber;//赠品编号
	
	private String attribute;//赠品属性
	
	private int quantity;//数量

	@OneToOne(cascade=CascadeType.ALL,fetch=FetchType.LAZY,mappedBy="dividend")//让这个外键生成到order表当中。
	@JoinColumn(name="order_id",referencedColumnName="order_id")
	private Order order;



注意：如果赠品是写成（不加@JoinColumn的情况）:
private String dividendId;//赠品ID

这个时候映射的时候就应该写成：
@JoinColumn(name="dividend_id",referencedColumnName="dividendId")
private Dividend dividend;//赠品

如果赠品是写成：
@Column(name="dividend_id")
private String dividendId;//赠品ID

这个时候映射的时候就应该写成：
@JoinColumn(name="dividend_id",referencedColumnName="dividend_id")
private Dividend dividend;//赠品

这两个第一个是给每取名字的取名字,取了名字的就叫名字。
第二个referencedColumnName就是指定这个关系是要映射到对方那个表的哪个字段上去的。




两边都加了 referencedColumnName 的时候结果如下：


mysql> show create table wxsc_dividend;
CREATE TABLE `wxsc_dividend` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `createTime` datetime NOT NULL,
  `updateTime` datetime NOT NULL,
  `version` int(11) NOT NULL,
  `attribute` varchar(255) DEFAULT NULL,
  `dividend_id` varchar(255) DEFAULT NULL,
  `dividend_name` varchar(255) DEFAULT NULL,
  `dividend_number` varchar(255) DEFAULT NULL,
  `quantity` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `dividend_id` (`dividend_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.01 sec)

mysql> show create table wxsc_order;
CREATE TABLE `wxsc_order` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `createTime` datetime NOT NULL,
  `updateTime` datetime NOT NULL,
  `version` int(11) NOT NULL,
  `consumer_remarks` longtext,
  `delivery_time` datetime DEFAULT NULL,
  `express_number` varchar(255) DEFAULT NULL,
  `freight_amount` float DEFAULT NULL,
  `invoice` varchar(255) DEFAULT NULL,
  `invoice_content` longtext,
  `invoice_head` longtext,
  `invoice_type` int(11) DEFAULT NULL,
  `order_id` varchar(255) DEFAULT NULL,
  `order_state` int(11) DEFAULT NULL,
  `order_time` datetime DEFAULT NULL,
  `payment_confirm_time` datetime DEFAULT NULL,
  `payment_time` datetime DEFAULT NULL,
  `seller_remarks` longtext,
  `total_sum` float DEFAULT NULL,
  `dividend_id` varchar(255) DEFAULT NULL,
  `subscriber_id` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `order_id` (`order_id`),
  KEY `FKD5D59A802C2E77E7` (`subscriber_id`),
  KEY `FKD5D59A804768DDC7` (`dividend_id`),
  CONSTRAINT `FKD5D59A804768DDC7` FOREIGN KEY (`dividend_id`) REFERENCES `wxsc_dividend` (`dividend_id`),
  CONSTRAINT `FKD5D59A802C2E77E7` FOREIGN KEY (`subscriber_id`) REFERENCES `wxsc_subscriber` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

数据库投射只@OneToMany的两个区别

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