如何使用HQL從多對多的表中獲得結果

Question

我有兩個表，僱員和項目，具有多對多的關係。我應該如何編寫HQL來獲取員工正在工作的所有項目？

Answer 1

您不需要編寫查詢。如果你已經建立了與@ManyToMany的關係，那麼你可以得到一個員工，然後employee.getProjects()將返回正確的數據。

public class Employee { 

    @ManyToMany(fetch = FetchType.EAGER) 
    @JoinTable(
      name = "employee_project", 
      joinColumns = @JoinColumn(name = "employee_id", referencedColumnName = "id"), 
      inverseJoinColumns = @JoinColumn(name = "project_id", referencedColumnName = "id") 
    ) 
    private Collection<Project> projects; 

} 

public class Project { 

    @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL) 
    @JoinTable(
      name = "employee_project", 
      joinColumns = @JoinColumn(name = "project_id", referencedColumnName = "id"), 
      inverseJoinColumns = @JoinColumn(name = "employee_id", referencedColumnName = "id") 
    ) 
    private Collection<Employee> employees; 

}