如果我在JPA实体之间存在多对多关系,如下所示,如何检索特定公司员工的Person列表(我对person属性感兴趣)?
PersonCompany之间的关系是多对多的。关系表Employee具有FK到PersonCompany,以及start_date和end_date,以指示雇佣开始和结束的时间。

@Entity
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "address")
    private String address;
}

@Entity
public class Company {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "address")
    private String address;
}

@Entity
public class CompanyEmployee {
    //note this is to model a relationship table. Am I doing this wrong?
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "start_date", nullable = false)
    private LocalDate startDate;

    @Column(name = "end_date", nullable = false)
    private LocalDate endDate;

    @ManyToOne
    private Company company;

    @ManyToOne
    private Person person;
}

我可以在@Query上使用CompanyEmployeeJPARepository吗?我该如何解决?
public interface CompanyEmployeeRepository extends JpaRepository<CompanyEmployee,Long> {
//
}

最佳答案

巴勃罗
我们公司正在将现有的 Spring / MyBatis 代码转换为 Spring Data JPA ,因此,我已经学习了 Spring Data JPA 几周了。我显然不是专家,但我提出了一个与您相似的示例,可能会对您有所帮助。

我有与您的类相似的PersonCompany类,但是(如Jens所述),您需要带有OneToMany批注的列表。我使用了一个单独的联接表(名为company_person),该表仅具有companyId和personId列,以维护多对多关系。请参见下面的代码。

我没有看到将开始/结束日期放在company_person连接表中的方法,因此我为此做了一个单独的(第4个表)。我用Java类实体EmploymentRecord称它为“employment_record”。它具有组合主键(companyId,personId)和开始/结束日期。

您需要用于“个人”,“公司”和“就业记录”的存储库。我扩展了CrudRepository而不是JpaRepository。但是,您不需要连接表(company_record)的实体或存储库。

我做了一个Spring Boot Application类来测试它。我在CascadeType.ALLPerson上使用了OneToMany。在我的应用程序测试中,我测试了我可以更改分配给一个人的公司,并且Spring Data将所有需要的更改传播到Company实体和联接表。

但是,我必须通过其存储库手动更新EmploymentRecord实体。例如,每次我向某人添加公司时,我都必须添加一个start_date。然后,在我从该人中删除该公司时添加一个end_date。可能有一些方法可以自动执行此操作。 Spring/JPA审核功能是可能的,因此请检查一下。

您问题的答案:



您只需使用companyRepository的findOne(Long id)方法,然后使用getPersonList()方法即可。

Application.java中的代码段:

PersonRepository pRep = context.getBean(PersonRepository.class);
CompanyRepository cRep = context.getBean(CompanyRepository.class);
EmploymentRecordRepository emplRep = context.getBean(EmploymentRecordRepository.class);

...

// fetch a Company by Id and get its list of employees
Company comp = cRep.findOne(5L);
System.out.println("Found a company using findOne(5L), company= " + comp.getName());
System.out.println("People who work at " + comp.getName());
for (Person p : comp.getPersonList()) {
    System.out.println(p);
}

以下是一些我发现有用的引用:

Spring Data JPA tutorial
Join Table example

Person.java:
@Entity
public class Person {

    // no-arg constructor
    Person() { }

    // normal use constructor
    public Person(String name, String address) {
        this.name = name;
        this.address = address;
    }

    @Id
    @GeneratedValue
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "address")
    private String address;

    @Version
    private int versionId;

    @OneToMany(cascade=CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinTable(name="company_person",
    joinColumns={@JoinColumn(name="person_id", referencedColumnName="id")},
    inverseJoinColumns={@JoinColumn(name="company_id", referencedColumnName="id")})
    private List<Company> companyList;

    // Getters / setters

}

Company.java:
@Entity
public class Company {

    // no-arg constructor
    Company() { }

    // normal use constructor
    public Company(String name, String address) {
        this.name = name;
        this.address = address;
    }

    @Id
    @GeneratedValue
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "address")
    private String address;

    @Version
    private int versionId;

    //@OneToMany(cascade=CascadeType.ALL)
    @OneToMany(fetch = FetchType.EAGER)
    @JoinTable(name="company_person",
    joinColumns={@JoinColumn(name="company_id", referencedColumnName="id")},
    inverseJoinColumns={@JoinColumn(name="person_id", referencedColumnName="id")})
    private List<Person> personList;

    // Getters / Setters
}

EmploymentRecord.java:
@Entity
@IdClass(EmploymentRecordKey.class)
public class EmploymentRecord {

    // no-arg constructor
    EmploymentRecord() { }

    // normal use constructor
    public EmploymentRecord(Long personId, Long companyId, Date startDate, Date endDate) {
        this.startDate = startDate;
        this.endDate = endDate;
        this.companyId = companyId;
        this.personId = personId;
    }

    // composite key
    @Id
    @Column(name = "company_id", nullable = false)
    private Long companyId;

    @Id
    @Column(name = "person_id", nullable = false)
    private Long personId;

    @Column(name = "start_date")
    private Date startDate;

    @Column(name = "end_date")
    private Date endDate;

    @Version
    private int versionId;

    @Override
    public String toString() {
        return
                " companyId=" + companyId +
                " personId=" + personId +
                " startDate=" + startDate +
                " endDate=" + endDate +
                " versionId=" + versionId;
    }

    // Getters/Setters

}

// Class to wrap the composite key
class EmploymentRecordKey implements Serializable {

    private long companyId;
    private long personId;

    // no arg constructor
    EmploymentRecordKey() { }

    @Override
    public int hashCode() {
        return (int) ((int) companyId + personId);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) return false;
        if (obj == this) return true;
        if (!(obj instanceof EmploymentRecordKey)) return false;
        EmploymentRecordKey pk = (EmploymentRecordKey) obj;
        return pk.companyId == companyId && pk.personId == personId;
    }

    // Getters/Setters
}

MySql脚本createTables.sql:
DROP TABLE IF EXISTS `test`.`company_person`;
DROP TABLE IF EXISTS `test`.`employment_record`;
DROP TABLE IF EXISTS `test`.`company`;
DROP TABLE IF EXISTS `test`.`person`;

CREATE TABLE `company` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(128) NOT NULL DEFAULT '',
  `address` varchar(500) DEFAULT '',
  `version_id` int NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `person` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(128) NOT NULL DEFAULT '',
  `address` varchar(500) DEFAULT '',
  `version_id` int NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/* Join table */
CREATE TABLE `company_person` (
  `company_id` int NOT NULL,
  `person_id` int NOT NULL,
  PRIMARY KEY (`person_id`,`company_id`),
  KEY `company_idx` (`company_id`),
  KEY `person_idx` (`person_id`),
  CONSTRAINT `fk_person` FOREIGN KEY (`person_id`) REFERENCES `person` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `fk_company` FOREIGN KEY (`company_id`) REFERENCES `company` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/* Employment records */
CREATE TABLE `employment_record` (
  `company_id` int NOT NULL,
  `person_id` int NOT NULL,
  `start_date` datetime,
  `end_date` datetime,
  `version_id` int NOT NULL,
  PRIMARY KEY (`person_id`,`company_id`),
  KEY `empl_company_idx` (`company_id`),
  KEY `empl_person_idx` (`person_id`),
  CONSTRAINT `fk_empl_person` FOREIGN KEY (`person_id`) REFERENCES `person` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `fk_empl_company` FOREIGN KEY (`company_id`) REFERENCES `company` (`id`) ON DELETE CASCADE ON UPDATE CASCADE

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

09-30 17:12
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