Spring data 数据库建表（一对一，一对多，多对多）

Spring data 数据库建表（一对一，一对多，多对多）

摘要: DBA 如果你在不学习编程，你将失业。如今我们对DBA的依赖越来越少，多数框架都支持实体关系映射，通过面向对象编程即可定义数据库结构。数据库设计也是在这个阶段完成的，不再需要DBA协助。如果DBA不学习怎样编写实体Class 最终将被淘汰。所以DBA除了会使用 ER图工具，还需要会写实体类。

Spring data 数据库建表（一对一，一对多，多对多） 

2017-07-25 景峯 Netkiller
本文节选择电子书《Netkiller Java 手札》
 
DBA 如果你在不学习编程，你将失业。如今我们对DBA的依赖越来越少，多数框架都支持实体关系映射，通过面向对象编程即可定义数据库结构。数据库设计也是在这个阶段完成的，不再需要DBA协助。如果DBA不学习怎样编写实体Class 最终将被淘汰。所以DBA除了会使用 ER图工具，还需要会写实体类。
 

8.3.1.9. @OneToOne

一对一表结构，如下面ER图所示，users表是用户表里面有登陆信息，profile 保存的时死人信息，这样的目的是我们尽量减少users表的字段，在频繁操作该表的时候性能比较好，另外一个目的是为了横向水平扩展。

+----------+             +------------+
| users    |             | profile    |
+----------+             +------------+
| id       | <---1:1---o | id         |
| name     |             | sex        |
| password |             | email      |
+----------+             +------------+

package com.example.api.domain.test;

import java.io.Serializable;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "users")
public class Users implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String name;
private String password;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}

@Override
public String toString() {
return "Users [id=" + id + ", name=" + name + ", password=" + password + "]";
}
}

package com.example.api.domain.test;

import java.io.Serializable;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "profile")
public class Profile implements Serializable {
/**
*
*/
private static final long serialVersionUID = -2500499458196257167L;
@Id
@OneToOne
@JoinColumn(name = "id")
private Users users;

private int age;
private String sex;
private String email;

public Users getUsers() {
return users;
}

public void setUsers(Users users) {
this.users = users;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getSex() {
return sex;
}

public void setSex(String sex) {
this.sex = sex;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

@Override
public String toString() {
return "Profile [users=" + users + ", age=" + age + ", sex=" + sex + ", email=" + email + "]";
}

}

CREATE TABLE `users` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(255) NULL DEFAULT NULL,
`password` VARCHAR(255) NULL DEFAULT NULL,
PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

CREATE TABLE `profile` (
`age` INT(11) NOT NULL,
`email` VARCHAR(255) NULL DEFAULT NULL,
`sex` VARCHAR(255) NULL DEFAULT NULL,
`id` INT(11) NOT NULL,
PRIMARY KEY (`id`),
CONSTRAINT `FK6x079ilawxjrfsljwyyi5ujjq` FOREIGN KEY (`id`) REFERENCES `users` (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

如果第二张表关联的并非主表的PK（主键）需要使用 referencedColumnName 指定。

@JoinColumn(name = "member_id",referencedColumnName="member_id")

8.3.1.10. OneToMany 一对多

我们要实现一个一对多实体关系，ER 图如下

+----------+          +------------+
| Classes  |          | Student    |
+----------+          +------------+
| id       | <---+    | id         |
| name     |     |    | name       |
+----------+     +--o | classes_id |
+------------+

classes 表需要 OneToMany 注解，Student 表需要 ManyToOne 注解，这样就建立起了表与表之间的关系

package com.example.api.domain.test;

import java.io.Serializable;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name="classes")
public class Classes implements Serializable{
/**
*
*/
private static final long serialVersionUID = -5422905745519948312L;
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int id;
private String name;

@OneToMany(cascade=CascadeType.ALL,mappedBy="classes")
private Set<Student> students;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Set<Student> getStudents() {
return students;
}

public void setStudents(Set<Student> students) {
this.students = students;
}

@Override
public String toString() {
return "classes [id=" + id + ", name=" + name + ", students=" + students + "]";
}
}

package com.example.api.domain.test;

import java.io.Serializable;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name = "student")
public class Student implements Serializable{
/**
*
*/
private static final long serialVersionUID = 6737037465677800326L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String name;

// 若有多个cascade，可以是：{CascadeType.PERSIST,CascadeType.MERGE}
@ManyToOne(cascade = { CascadeType.ALL })
@JoinColumn(name = "classes_id")
private Classes classes;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Classes getClasses() {
return classes;
}

public void setClasses(Classes classes) {
this.classes = classes;
}

@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", classes=" + classes + "]";
}

}

最终 SQL 表如下

CREATE TABLE `classes` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(255) NULL DEFAULT NULL,
PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

CREATE TABLE `student` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(255) NULL DEFAULT NULL,
`class_id` INT(11) NULL DEFAULT NULL,
PRIMARY KEY (`id`),
INDEX `FKnsl7w2nw6o6eq53hqlxfcijpm` (`class_id`),
CONSTRAINT `FKnsl7w2nw6o6eq53hqlxfcijpm` FOREIGN KEY (`class_id`) REFERENCES `classes` (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

Classes classes=new Classes();
classes.setName("One");

Student st1=new Student();
st1.setSname("jason");
st1.setClasses(classes);
studentRepostitory.save(st1);

Student st2=new Student();
st2.setSname("neo");
st2.setClasses(classes);
studentRepostitory.save(st2);

8.3.1.11. ManyToMany 多对多

用户与角色就是一个多对多的关系，多对多是需要中间表做关联的。所以我方需要一个 user_has_role 表。

+----------+          +---------------+            +--------+
| users    |          | user_has_role |            | role   |
+----------+          +---------------+            +--------+
| id       | <------o | user_id       |      /---> | id     |
| name     |          | role_id       | o---+      | name   |
| password |          |               |            |        |
+----------+          +---------------+            +--------+

创建 User 表

package com.example.api.domain.test;

import java.io.Serializable;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.JoinColumn;

@Entity
@Table(name = "users")
public class Users implements Serializable {
/**
*
*/
private static final long serialVersionUID = -2480194112597046349L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String name;
private String password;

@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "user_has_role", joinColumns = { @JoinColumn(name = "user_id", referencedColumnName = "id") }, inverseJoinColumns = { @JoinColumn(name = "role_id", referencedColumnName = "id") })
private Set<Roles> roles;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}

public Set<Roles> getRoles() {
return roles;
}

public void setRoles(Set<Roles> roles) {
this.roles = roles;
}

@Override
public String toString() {
return "Users [id=" + id + ", name=" + name + ", password=" + password + ", roles=" + roles + "]";
}

}

创建 Role 表

package com.example.api.domain.test;

import java.io.Serializable;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name = "roles")
public class Roles implements Serializable {
private static final long serialVersionUID = 6737037465677800326L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String name;
@ManyToMany(mappedBy = "roles")
private Set<Users> users;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Set<Users> getUsers() {
return users;
}

public void setUsers(Set<Users> users) {
this.users = users;
}

@Override
public String toString() {
return "Roles [id=" + id + ", name=" + name + ", users=" + users + "]";
}

}

最终产生数据库表如下

CREATE TABLE `users` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(255) NULL DEFAULT NULL,
`password` VARCHAR(255) NULL DEFAULT NULL,
PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

CREATE TABLE `roles` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(255) NULL DEFAULT NULL,
PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

CREATE TABLE `user_has_role` (
`user_id` INT(11) NOT NULL,
`role_id` INT(11) NOT NULL,
PRIMARY KEY (`user_id`, `role_id`),
INDEX `FKsvvq61v3koh04fycopbjx72hj` (`role_id`),
CONSTRAINT `FK2dl1ftxlkldulcp934i3125qo` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`),
CONSTRAINT `FKsvvq61v3koh04fycopbjx72hj` FOREIGN KEY (`role_id`) REFERENCES `roles` (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

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