JPA / Hibernate查询速度太慢，查询太多

Question

我有两个实体Employee和Department

Employee实体是我的应用程序的只读数据集（我不拥有此表）

支持我拥有的Department实体的表数据。如果我在没有注释Employee到Department实体关系的情况下查询我的Employee实体，则查询是超高速的，因为它只产生一个SQL调用。

只要我将Department关系注释到Employee实体，就会有大量的SQL调用。以下是我认为每个实体帮助获得帮助的相关细节：

@Entity
Employee
@Id
String employee_number;
String first_name;
String last_name;
String phone_number;
@Column(name="dept")
private String home_dept_number;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="dept", referencedColumnName="dept_number", insertable = false, updatable = false)
@NotFound(action = NotFoundAction.IGNORE)
private Department department;


@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="dept", referencedColumnName="department_number", insertable = false, updatable = false)

---

@Entity    
Department
@Id
String dept_number
String dept_name;

@OneToOne(fetch = FetchType.LAZY)
@NotFound(action=NotFoundAction.IGNORE)
@JoinColumn(name = "department_manager_id", referencedColumnName = "employee_number")
private Employee departmentManager;

@OneToOne(fetch = FetchType.LAZY)
@NotFound(action=NotFoundAction.IGNORE)
@JoinColumn(name = "department_admin_aide_id", referencedColumnName = "employee_number")
private Employee departmentAdminAide;

@OneToOne(fetch = FetchType.LAZY)
@NotFound(action=NotFoundAction.IGNORE)
@JoinColumn(name = "department_rep_id", referencedColumnName = "employee_number")
private Employee departmentRepresentative;

Answer 1

我的猜测是缓慢是由@NotFound注释引起的：Hibernate可能被迫检查部门是否确实存在。

使用@NotFound可以弥补员工引用不存在的部门的不一致数据库。如果您的数据库是一致的（并且应该由外键约束强制执行），则不需要这些注释。