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[英]Unable to persist data into mysql database using spring + spring data jpa, Why?
[英]Why will foreign key data will not persist to mysql database?
我正在使用Java使用基本的mySQL关系数据库。 我已为具有1:M关系的两个表附加了实体类。 我已经在实体表中定义了“ 1对很多”关系。 在Projects类中,我想同时声明外键(私有int contractor_id)以及getter和setter(如注释所示),但是我不断收到编译错误,指出以下内容*项目[field.projects.com.cn]存在多个可写映射。 contractor_id。 只能将其中一个定义为可写,所有其他都必须指定为只读。*因此,由于在BusinessAccount类中已经设置了它们的值,因此我将它们注释掉。 现在,已使用我显示的“ addProject()”方法将数据持久保存到数据库中。 但是,字段contractor_id(即外键)作为null传递给Projects表。 我有一个用于会话的contractor_id的值(名为sessionContractorId),但由于没有此表的设置程序,因此无法将其传递给数据库。 关于如何将数据库外键的值持久化的任何建议将不胜感激。
@Entity
@Table(name = "business_accounts")
public class BusinessAccount {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
@Column(name = "first_name")
private String firstName;
@Column(name = "surname")
private String surname;
@OneToMany(mappedBy = "businessAccount", fetch = FetchType.EAGER, cascade = { CascadeType.ALL })
private List<Projects> projects;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getSurname() {
return surname;
}
public void setSurname(String surname) {
this.surname = surname;
}
public List<Projects> getProjects()
{
if (projects == null)
{
projects = new ArrayList<Projects>();
}
return projects;
}
public void setProjects(List<Projects> projects)
{
this.projects = projects;
}
}
@Entity
@Table(name = "projects")
public class Projects {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int project_id;
@Column(name = "project_name")
private String projectName;
@Column(name = "project_description")
private String projectDescription;
//@Column(name = "contractor_id")
//private int contractorId;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumns({ @JoinColumn(name = "contractor_id", referencedColumnName="id") })
private BusinessAccount businessAccount;
public BusinessAccount getBusinessAccount() {
if (businessAccount == null) {
businessAccount = new BusinessAccount();
}
return businessAccount;
}
public void setBusinessAccount(BusinessAccount businessAccount) {
this.businessAccount = businessAccount;
}
public int getProject_id() {
return project_id;
}
public void setProject_id(int project_id) {
this.project_id = project_id;
}
public String getProjectName() {
return projectName;
}
public void setProjectName(String projectName) {
this.projectName = projectName;
}
public String getProjectDescription() {
return projectDescription;
}
public void setProjectDescription(String projectDescription) {
this.projectDescription = projectDescription;
}
//public int getContractorId() {
//return contractorId;
//}
//public void setContractorId(int contractorId) {
//this.contractorId = contractorId;
//}
}
@ManagedBean
@ViewScoped
public class ProjectBean implements Serializable {
private static final long serialVersionUID = -2107387060867715013L;
private static final String PERSISTENCE_UNIT_NAME = "NeedABuilderUnit";
private static EntityManagerFactory factory;
private Projects projects;
private List<BusinessAccount> businessAccount;
public ProjectBean() {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
EntityManager em = factory.createEntityManager();
List<BusinessAccount> businessAccount = em.createQuery("from BusinessAccount a", BusinessAccount.class)
.getResultList();
em.close();
setBusinessAccount(businessAccount);
}
@PostConstruct
public void init() {
projects = new Projects();
}
public String addProject() {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
EntityManager em = factory.createEntityManager();
em.getTransaction().begin();
String sessionEmail=Util.getEmail();
Query myQuery = em.createQuery("SELECT u FROM BusinessAccount u WHERE u.email=:email");
myQuery.setParameter("email", sessionEmail);
List<BusinessAccount> accounts=myQuery.getResultList();
int sessionContractorId=accounts.get(0).getId();
em.persist(projects);
em.getTransaction().commit();
em.close();
return "success";
}
我注意到有关代码的两件事。
首先,代码应使用实体,并忽略特定实体的id
字段。 因此,当您提取帐户时,它应该获取实体而不是ID:
//Don't do this
List<BusinessAccount> accounts=myQuery.getResultList();
int sessionContractorId=accounts.get(0).getId();
//Instead do this
List<BusinessAccount> accounts=myQuery.getResultList();
BusinessAccount account =accounts.get(0); //hopefully an account exists
其次,在JPA中,您负责管理关联双方。 因此,您必须将Account
添加到Project
并在关系的另一侧为Account
设置Project
。 我从没在代码中看到这种情况,仅看到持久化的projects
(不确定其来源)。 假设projects
是一个List<Project>
,它将看起来像这样:
public String addProject() {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
EntityManager em = factory.createEntityManager();
em.getTransaction().begin();
String sessionEmail=Util.getEmail();
Query myQuery = em.createQuery("SELECT u FROM BusinessAccount u WHERE u.email=:email");
myQuery.setParameter("email", sessionEmail);
List<BusinessAccount> accounts=myQuery.getResultList();
BusinessAccount account =accounts.get(0);
projects.setBusinessAccount(account); //managing both sides
account.getProjects().add(projects); //managing both sides
em.persist(projects);
em.getTransaction().commit();
em.close();
return "success";
}
附带说明一下,您可能希望将类名更改为Project
并使用变量名project
因为它可以更准确地描述关系。 同样,由于您正在创建一个新Project
您将需要实例化List<BusinessAccount>
:
List<BusinessAccount> projects = new ArrayList<BusinessAccount>();
希望这能解决您的问题,我建议您观看我在双向一对多关系上创建的此视频教程 。
您应该使用@JoinColumn(name="id_user", insertable = false, updatable = false)
请参考: JPA中的多个可写映射?
希望这可以帮助 :)
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