[英]JPA Query and Relations
我正在開發一個HRM應用程序,所以我對如何通過JPA管理實體感到困惑。
我恢復的情況是多語言環境中的一組表:-employees -departments -languages -departments_languages
跟隨我的數據庫表:
員工實體類:
@Entity
@Table(name="employees")
@NamedQuery(name="Employee.findAll", query="SELECT e FROM Employee e")
public class Employee implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="employeed_id", unique=true, nullable=false)
private int employeedId;
@Column(nullable=false, length=255)
private String address;
@Temporal(TemporalType.DATE)
@Column(nullable=false)
private Date birthday;
...
//bi-directional many-to-one association to Department
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="department_id", nullable=false)
private Department department
}
部門實體班
@Entity
@Table(name="departments")
@NamedQuery(name="Department.findAll", query="SELECT d FROM Department d")
public class Department implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="department_id", unique=true, nullable=false)
private int departmentId;
@Temporal(TemporalType.TIMESTAMP)
@Column(name="date_added", nullable=false)
private Date dateAdded;
@Column(name="location_id", nullable=false)
private int locationId;
@Column(nullable=false)
private byte status;
//bi-directional many-to-one association to DepartmentsLanguage
@OneToMany(mappedBy="department")
private Set<DepartmentsLanguage> departmentsLanguages;
//bi-directional many-to-one association to Employee
@OneToMany(mappedBy="department",fetch=FetchType.LAZY)
private Set<Employee> employees;
...
}
部門語言實體
@Entity
@Table(name="departments_languages")
@NamedQuery(name="DepartmentsLanguage.findAll", query="SELECT d FROM DepartmentsLanguage d")
public class DepartmentsLanguage implements Serializable {
private static final long serialVersionUID = 1L;
@EmbeddedId
private DepartmentsLanguagePK id;
@Column(length=255)
private String description;
@Column(length=255)
private String name;
//bi-directional many-to-one association to Department
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="department_id", nullable=false, insertable=false, updatable=false)
private Department department;
//bi-directional many-to-one association to Language
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="language_id", nullable=false, insertable=false, updatable=false)
private Language language;
...
}
事實上,我問你是否是一種正確的方法,我如何執行JPA查詢:
SELECT * FROM employees
INNER JOIN departments_languages using(department_id)
WHERE employeed_id = 1 and language_id = 1
從這個查詢我需要員工信息,部門名稱(假設languageId為1)
從eclipse執行查詢JPA控制台返回具有所有關系的Employee對象,但都返回所有相關結果
你能告訴我這種設計的樣本查詢嗎?
解決了使用獲取連接實現查詢,例如:
Query query = entityManager.createQuery("select e from Employee as e "
+ "JOIN FETCH e.department d "
+ "JOIN FETCH d.departmentsLanguages dl "
+ "where e.employeedId = :employeeId "
+ "and dl.language = :languageId");
您還可以使用EntiyGraph功能來提高JPA風格的性能;)
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