继承映射
如果只想要生成一张表，可以指定映射策略
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@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
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简单用法
父：
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import lombok.Data;
import javax.persistence.*;
import java.io.Serializable;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@Entity
@Data
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class People implements Serializable {
private static final long serialVersionUID = 6254092813095169295L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
protected Integer id;
protected String name;
}
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import com.scan.test.People;
import lombok.Data;
import lombok.EqualsAndHashCode;
import javax.persistence.Column;
import javax.persistence.Entity;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@EqualsAndHashCode(callSuper = true)
@Entity
@Data
public class Student extends People {
private static final long serialVersionUID = 2241366750854518413L;
private int className;
}
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获得一张表
CREATE TABLE people (
dtype varchar(31) NOT NULL,
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(255) DEFAULT NULL,
class_name int(11) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
注意：无论多少子类都只生成一张表，通过dtype字段区分不同子类。应用场景为同一种类多个对象的数据储存
实验在父对象添加属性，在数据库能否生成成功
复杂用法
父：
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import lombok.Data;
import javax.persistence.*;
import java.io.Serializable;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@Entity
@Data
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@Table(indexes = {@Index(columnList = "uid", unique = true),
@Index(columnList = "studentUid")})
public class People implements Serializable {
private static final long serialVersionUID = 6254092813095169295L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
protected Integer id;
protected Integer uid;
protected Integer studentUid;
protected String name;
}
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import com.scan.test.People;
import lombok.Data;
import lombok.EqualsAndHashCode;
import javax.persistence.Column;
import javax.persistence.Entity;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@EqualsAndHashCode(callSuper = true)
@Entity
@Data
public class Student extends People {
private static final long serialVersionUID = 2241366750854518413L;
@Column(unique = true)
private int className;
}
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获得表：
CREATE TABLE people (
dtype varchar(31) NOT NULL,
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(255) DEFAULT NULL,
student_uid int(11) DEFAULT NULL,
uid int(11) DEFAULT NULL,
class_name int(11) DEFAULT NULL,
PRIMARY KEY (id),
UNIQUE KEY UK98584pow8829ecp9w7fwbvocw (uid),
UNIQUE KEY UK_n00mlaw19y2hphh71hwt4lc3l (class_name),
KEY IDXjt0gho5f24xg5n8c710r8723a (student_uid)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
不管是父类和子类添加的属性都在数据表映射成功
还可以指定其他两种映射策略，这边就不展开讲
部分继承
只有子类会生成数据表，父类的属性同样会写进子类的表中
简单用法
父：
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import lombok.Data;
import javax.persistence.*;
import java.io.Serializable;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@Data
@MappedSuperclass
public class People implements Serializable {
private static final long serialVersionUID = 6254092813095169295L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
protected Integer id;
protected String name;
}
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import com.scan.test.People;
import lombok.Data;
import lombok.EqualsAndHashCode;
import javax.persistence.Column;
import javax.persistence.Entity;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@EqualsAndHashCode(callSuper = true)
@Entity
@Data
public class Student extends People {
private static final long serialVersionUID = 2241366750854518413L;
private int className;
}
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创建数据表：
CREATE TABLE student (
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(255) DEFAULT NULL,
class_name int(11) NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
注意：是使用子类生成的数据表，子类的数据表会包含父类的属性对象，并且继承的父类的id定义
复杂用法
父：
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import lombok.Data;
import javax.persistence.*;
import java.io.Serializable;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@MappedSuperclass
@Data
@Table(indexes = {@Index(columnList = "uid", unique = true),
@Index(columnList = "studentUid")})
public class People implements Serializable {
private static final long serialVersionUID = 6254092813095169295L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
protected Integer id;
protected Integer uid;
protected Integer studentUid;
protected String name;
}
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import com.scan.test.People;
import lombok.Data;
import lombok.EqualsAndHashCode;
import javax.persistence.Column;
import javax.persistence.Entity;
/**
* @author: thy
* @date: 2019/9/4
* @description:
*/
@EqualsAndHashCode(callSuper = true)
@Entity
@Data
public class Student extends People {
private static final long serialVersionUID = 2241366750854518413L;
private int className;
}
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创建数据表：
CREATE TABLE student (
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(255) DEFAULT NULL,
student_uid int(11) DEFAULT NULL,
uid int(11) DEFAULT NULL,
class_name int(11) NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
注意：@table定义的索引都没有成功。在使用@MappedSuperclass的时候需要注意，因为父类不是entity对于table的定义在父类都不会生效。只有是针对属性的定义能够在子类生成的数据表里面映射
https://blog.csdn.net/heardy/article/details/7924192
https://www.ibm.com/developerworks/cn/java/j-lo-hibernatejpa/index.html
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