假设我有两个实体,Employee
并且Skill
. 每个员工都有一套技能。现在,当我通过实例懒惰地加载技能时Employee
,缓存不用于不同实例中的技能Employee
。
让我们考虑以下数据集。
Employee - 1 : Java, PHP
Employee - 2 : Java, PHP
当我在 Employee - 1 之后加载 Employee - 2 时,我不希望 hibernate 访问数据库来获取技能,而是使用Skill
缓存中已经可用的实例。这可能吗?如果有怎么办?
休眠配置
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.password">pass</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost/cache</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>
<property name="hibernate.cache.provider_class">net.sf.ehcache.hibernate.EhCacheProvider</property>
<property name="hibernate.hbm2ddl.auto">update</property>
<property name="hibernate.show_sql">true</property>
<mapping class="org.cache.models.Employee" />
<mapping class="org.cache.models.Skill" />
</session-factory>
删除了导入、getter 和 setter 的实体
@Entity
@Table(name = "employee")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String name;
public Employee() {
}
@ManyToMany
@JoinTable(name = "employee_skills", joinColumns = @JoinColumn(name = "employee_id"), inverseJoinColumns = @JoinColumn(name = "skill_id"))
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
private List<Skill> skills;
}
@Entity
@Table(name = "skill")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Skill {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private String name;
}
加载第二个员工及其技能的 SQL
Hibernate: select employee0_.id as id0_0_, employee0_.name as name0_0_ from employee employee0_ where employee0_.id=?
Hibernate: select skills0_.employee_id as employee1_1_, skills0_.skill_id as skill2_1_, skill1_.id as id1_0_, skill1_.name as name1_0_ from employee_skills skills0_ left outer join skill skill1_ on skills0_.skill_id=skill1_.id where skills0_.employee_id=?
我特别想避免第二个查询,因为第一个查询无论如何都是不可避免的。