JPA 级联保存的问题

前提：系统有学校-学生关系，学校能够包含多个学生，学生只能属于一个学校

在使用 spring-data-jpa 的时候，保存学校的同时保存学生信息，不须要先逐个保存学生信息，再将学生信息放在学校中保存学校

首先spring data jpa 配置须要设置数据库方言，不然回有外键不生效的

spring: datasource: url: jdbc:mysql://localhost:3306/iot?serverTimezone=GMT%2B8&autoReconnect=true&useUnicode=yes&characterEncoding=UTF-8&useSSL=false driver-class-name: com.mysql.cj.jdbc.Driver username: root password: 123456 jpa: show-sql: true hibernate: ddl-auto: update # 不增长出问题 database-platform: org.hibernate.dialect.MySQL5InnoDBDialect

学校信息：

@Entity(name = "t_school") @Data @ToString(exclude = "students") public class School { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private int id; private String name; 
　　 //一对多 @OneToMany(fetch = FetchType.EAGER,mappedBy = "school",cascade = CascadeType.ALL) private List<Student> students = new ArrayList<>(); public void addStudent(Student stu){ if(stu != null){ students.add(stu); } } }

学生信息：

@Entity(name = "t_student") @Data @ToString(exclude = "school") public class Student { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private int id; private String name; 
　　//多对一 @ManyToOne(cascade = CascadeType.ALL) @JoinColumn(name = "school_id",nullable = false) @JsonIgnore @JsonIgnoreProperties private School school; }

测试、保存学校信息

@RestController public class TestController { @Autowired private SchoolRepository schoolRepository; @GetMapping("/save") public void save(){ School school = new School(); school.setName("北京中学"); Student student = new Student(); student.setName("张三");  student.setSchool(school); Student student2 = new Student(); student2.setName("李四");  student2.setSchool(school); school.addStudent(student); school.addStudent(student2); System.out.println(school); schoolRepository.saveAndFlush(school); } }

在新建一方信息，将多方信息保存在一方的集合列表中，若是没有设置 一方的信息，将致使保存多方抱错，外键id 不能为 null

student2.setSchool(school);

最后只须要保存一方信息，便可以将多方的信息一块儿保存

schoolRepository.saveAndFlush(school);