java - 休眠中的 OneToMany 映射。值即将为空
问题描述
我有一个学生班,我有一个具有@OneToMany 关系的Account 班。一个学生到多个帐户。我的两个表都已创建。我的帐户表中有一个字段 Student_id,但值为 null。你能帮我在哪里做错吗。
import java.util.Collection;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table;
@Entity
@Table(name = "Student_Information")
public class Student {
@Id
private int id;
@Column
private String name;
@OneToOne(targetEntity=Address.class , cascade = CascadeType.ALL)
@JoinColumn(name="addressId" , referencedColumnName = "addressId")
private Address adId;
@OneToMany(mappedBy="student",cascade= CascadeType.ALL)
private Collection<Account> account;
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "STUDENT_CERTIFICATION", joinColumns = { @JoinColumn(name = "id") }, inverseJoinColumns = { @JoinColumn(name = "certId") })
private Collection<Certification> certId;
public Collection<Account> getAccount() {
return account;
}
public void setAccount(Collection<Account> account) {
this.account = account;
}
public Collection<Certification> getCertId() {
return certId;
}
public void setCertId(Collection<Certification> certId) {
this.certId = certId;
}
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 Address getAdId() {
return adId;
}
public void setAdId(Address adId) {
this.adId = adId;
}
}
Account Class
import javax.persistence.CascadeType;
import javax.persistence.Column;
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 = "Account")
public class Account {
@Id
private int accountId;
@Column
private String accountNumber;
@ManyToOne
@JoinColumn(name="id")
private Student id;
public Student getId() {
return id;
}
public void setId(Student id) {
this.id = id;
}
public int getAccountId() {
return accountId;
}
public void setAccountId(int accountId) {
this.accountId = accountId;
}
public String getAccountNumber() {
return accountNumber;
}
public void setAccountNumber(String accountNumber) {
this.accountNumber = accountNumber;
}
}
我有一个学生班,我有一个具有@OneToMany 关系的Account 班。一个学生到多个帐户。我的两个表都已创建。我的帐户表中有一个字段 Student_id,但值为 null。你能帮我在哪里做错吗。
解决方案
我认为问题在于连接列注释中的名称,该名称应与表中列的实际名称匹配,在这种情况下,正如您所说的 student_id
@ManyToOne
@JoinColumn(name="student_id")
private Student id;
推荐阅读
- java - 用 Java 流替换循环和用法
- python - 新用户在 Python 中使用四舍五入计算器时遇到问题
- python - 如何在 Python 中将列表组合成 1 个字典
- python - 通过另一个脚本运行一个脚本不理解 PIL
- python - Python - 多个 os.system 命令的替代方案
- ios - IAP.getProducts 得到空响应
- git - 这个变基从哪里来?
- firebase - 如何删除名称中包含 Return 和 Tab 字符的集合
- python - 如何使用来自夹具外部设置夹具的变量
- react-native - 如何在本机反应中仅选择没有标志的国家代码