Hibernate onetoMany映射检索链中的所有结果

本文介绍了Hibernate onetoMany映射检索链中的所有结果的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 假设我有两张名为employee和phone_number的表，其中员工可以有多个号码。 我有两个表格： 1）员工列： id 名称 2）phone_number 列： employee_id（FK） phone_number_type phone_number 雇员和phone_number与一个到多个映射（phone_number中的employee_id列充当FK） 我已经在模型类中定义了以下注释。 @Entity @Table（name =employee） public class Employee @Id @GeneratedValue 私人整数ID; @OneToMany（fetch = FetchType.LAZY，mappedBy =employee_id） @JoinColumn（name =ID） private设置< PhoneNumber> phonenumbers = new HashSet< PhoneNumber>（0）; public Set< PhoneNumber> getPhonenumbers（）{返回phonenumbers; } public void setPhoneNumbers（Set< PhoneNumber> phonenumbers）{ this.phonenumbers = phonenumbers; 类PhoneNumber public class PhoneNumber { @ManyToOne（fetch = FetchType.LAZY）pre $ @Entity @Table @JoinColumn（name =employee_id）私人雇员employeeid; public Employee getEmployeeid（）{ return this.employeeid; } public void setEmployeeid（Employee employeeid）{ this.employeeid = employeeid; } 我的问题是当我检索所有员工或特定员工时，检索他们的电话号码。目前，当我在调试模式下运行时，我看不到正在填充的电话号码。我在springmvc框架中运行hibernate，并通过以下代码检索员工： @Override @SuppressWarnings （未选中）公共列表<雇员> getEmployees（）{ // TODO自动生成的方法存根 return getCurrentSession（）。createQuery（from Employees）。list（）; } 他们需要做什么才能返回phone_numbers。我的最终目标是在视图中以表格格式显示员工和电话号码。 谢谢 列表< Employees>如何确保它正在提取电话数据？ _employees = employeeService.getEmployees（）; for（Employees o：_employees）{ java.util.Set< PhoneNumber> a = o.getPhonenumbers（）; } 我发现了我所犯的错误，但我正遇到另一个问题。 我的错误是employee_id字段是FK，但没有正确填充。但是，此列不是phone_number表中的主键。 我将phone_number更改为： @Entity @Table（name =phonenumber） public class Phonenumber { @EmbeddedId @ManyToOne（fetch = FetchType.EAGER） @JoinColumn（name =EMPLOYEEID）私人雇员employeeid; 但是，我现在遇到以下错误：导致：org.hibernate.MappingException ：Composite-id类必须实现Serializable： 我能够摆脱这个错误，但我遇到了另一个有趣的错误。 @Entity @Table（name =phonenumber）它只是选择电话号码中的第一行。 public class Phonenumber implements Serializable { @Column（name =key） private String key; @Column（name =value） private String value; @Id @ManyToOne（fetch = FetchType.EAGER） @JoinColumn（name =EMPLOYEEID）私人员工雇员; 员工 @Entity @Table（name =employee） public class Employee { @Id @GeneratedValue private Integer id ; @OneToMany（mappedBy =employeeid，fetch = FetchType.EAGER） private Set< Phonenumber> phonenumbers = new HashSet< Phonenumber>（0）; 解决方案 使用 HQL 可以如下实现： createQuery（from employee e left join fetch e.phonenumbers） 您也可以使用 EAGER加载。但是，要非常小心并考虑其影响。 它可能会影响性能，因为它会加载所有相关的实体。 在中不需要@ JoinColumn 因为通过 mappedBy 你说你想如何加入实体。在大多数情况下， @JoinColumn 用于单向关系，或者当您没有 mappedBy 时。 请从Phonenumber的员工列删除@Id，并让 id 为主键。 @Entity @Table（name =phonenumber） public class Phonenumber implements Serializable { @Column（name =key） private String key; @Column（name =value） private String value; @Id @GeneratedValue 私人整数ID; @ManyToOne（fetch = FetchType.EAGER）私人雇员雇员; } Say I have two tables called employee and phone_number where employee can have multiple numbers.I have two tables for example:1) employeecolumns:idname2) phone_numbercolumns:employee_id(FK)phone_number_typephone_numberemployee and phone_number have one to many mappings with (employee_id column in phone_number acting as a FK)I have defined following annotations in the model classes.@Entity@Table(name="employee")public class Employee@Id@GeneratedValueprivate Integer id;@OneToMany(fetch = FetchType.LAZY, mappedBy="employee_id")@JoinColumn(name = "ID")private Set<PhoneNumber> phonenumbers = new HashSet<PhoneNumber>(0);public Set<PhoneNumber> getPhonenumbers() {return phonenumbers; }public void setPhoneNumbers(Set<PhoneNumber> phonenumbers) {this.phonenumbers = phonenumbers; }Class PhoneNumber@Entity@Table(name="phone_number")public class PhoneNumber {@ManyToOne(fetch = FetchType.LAZY)@JoinColumn(name = "employee_id")private Employee employeeid;public Employee getEmployeeid() {return this.employeeid;}public void setEmployeeid(Employee employeeid) {this.employeeid = employeeid;}My question is When I retrieve all the employees or a specific employee I also want to retrieve their phone numbers. Currently, when I run in debug mode I cannot see the phone number being populated. I am running the hibernate in springmvc framework and I am retrieving the employee through following code:@Override@SuppressWarnings("unchecked")public List<Employees> getEmployees() { // TODO Auto-generated method stub return getCurrentSession().createQuery("from Employees").list();}Is their anything extra I need to do to return the phone_numbers. My end goal is to display the employees and the phone number in a table format in the view.Thank youWhen I made the "fetch = EAGER" I tried to debug but I didnt see values. How do I make sure that it is pulling the phone data?List<Employees> _employees= employeeService.getEmployees(); for (Employees o: _employees) { java.util.Set<PhoneNumber> a = o.getPhonenumbers(); }I found the mistake that I had made but I am running into another issue.My mistake was that the employee_id field is the FK but it was not populated properly. However, this column is not the primary key in the phone_number table.I changed the phone_number to be following:@Entity@Table(name="phonenumber")public class Phonenumber { @EmbeddedId @ManyToOne(fetch=FetchType.EAGER) @JoinColumn(name = "EMPLOYEEID") private Employee employeeid;However, I am getting following error now:Caused by: org.hibernate.MappingException: Composite-id class must implement Serializable:I am able to get rid of this error but I am running into another interesting error. It is only selecting the first row in the phonenumber.@Entity@Table(name="phonenumber")public class Phonenumber implements Serializable { @Column(name="key") private String key; @Column(name="value") private String value; @Id @ManyToOne(fetch=FetchType.EAGER) @JoinColumn(name = "EMPLOYEEID") private Employee employee;Employee@Entity@Table(name="employee")public class Employee{ @Id @GeneratedValue private Integer id; @OneToMany(mappedBy = "employeeid", fetch = FetchType.EAGER) private Set<Phonenumber> phonenumbers= new HashSet<Phonenumber>(0); 解决方案 Using HQL it could be achieved as follows: createQuery("from employee e left join fetch e.phonenumbers")As alternative you could use EAGER loading. However, be very careful and consider implications. It could impact performance because it loads all related entities. There is no need in @JoinColumn because by means of mappedBy you said how you want to join entities. In most cases @JoinColumn used for uni-directional relationships or when you don't have mappedBy. Please remove @Id from employee column in Phonenumber and let id be primary key. @Entity@Table(name="phonenumber")public class Phonenumber implements Serializable { @Column(name="key") private String key; @Column(name="value") private String value; @Id @GeneratedValue private Integer id; @ManyToOne(fetch=FetchType.EAGER) private Employee employee;} 这篇关于Hibernate onetoMany映射检索链中的所有结果的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！