java - 关系表的 Spring JPA Repository 查询过滤器

Question

如果我在 JPA 实体之间有如下所示的多对多关系，我如何检索属于特定公司员工的 Person 列表(我对 person 属性感兴趣) ？

Person 和Company 之间的关系是多对多的。关系表 Employee 具有到 Person 和 Company 的 FK，以及一个 start_date 和 end_date 来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;
}

我是否在 CompanyEmployeeJPARepository 上使用了 @Query？我该如何应对？

public interface CompanyEmployeeRepository extends JpaRepository<CompanyEmployee,Long> {
//
}

Answer 1

巴勃罗，
我们公司正在将我们现有的Spring/MyBatis代码转换为Spring Data JPA，所以我一直在学习Spring Data JPA 几个星期。我显然不是专家，但我想出了一个类似于您的示例，可能会对您有所帮助。

我有 Person 和 Company 类，它们与您的类似，但是(正如 Jens 提到的)，您需要带有 OneToMany 注释的列表。我使用了一个单独的连接表(名为 company_person)，它只有 companyId、personId 列来维护多对多 关系。请参阅下面的代码。

我没有找到将开始/结束日期放入 company_person 连接表的方法，因此我为此制作了一个单独的(第 4 个表)。我用 Java 类实体 EmploymentRecord 将其命名为 employment_record。它具有组合主键(companyId、personId)和开始/结束日期。

您需要 Person、Company 和 EmploymentRecord 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 Person 的 OneToMany 上使用了 CascadeType.ALL。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 实体和连接表。

但是，我必须通过其存储库手动更新 EmploymentRecord 实体。例如，我每次为一个人添加公司时都必须添加一个 start_date。然后，在我从那个人那里删除那家公司时添加一个结束日期。可能有某种方法可以自动执行此操作。 Spring/JPA 审计功能是可能的，所以检查一下。

问题的答案:

how can I retrieve a list of Person (I am interested in the person attributes) that are employees of a specific company?

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

来自 Application.java 的片段:

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);
}

以下是我认为有用的一些引用资料:

Spring Data JPA tutorial
Join Table example

人.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

}

公司.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
}

就业记录.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;