JPA 2.0/Hibernate-为什么Hibernate在删除之前发出select count（*）查询

我将spring数据与hibernate一起使用。我有一个双向映射，如下所示：

public class Student {
   ...
   @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true,    mappedBy="student")
   private List<StudentLog> logs = newArrayList();  
   ...
}

public class StudentLog {
   .....
    @ManyToOne(cascade = CascadeType.REFRESH, optional = false, fetch = FetchType.LAZY)
    @JoinColumn(name = "STUDENT_ID" , insertable = true, updatable = false, nullable =false)
    private Student student;
   .....
}

知道hibernate为什么发出2个select查询吗？是否不可能只发出删除查询而不发出选择

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谢谢

JPA仅在

EntityManager

上公开一个

remove（…）

方法，该方法将删除实体。因此，对于使用id调用

delete（…）

，我们首先检查具有id的实体是否确实存在（第一次查询）。然后，我们具体化对象（第二个查询），最终将其交给

EntityManager.remove（…）

（查询3和查询4）

---

实际上，

存在（…）

检查是多余的，因为我们可以在第二步中简单地检查

null

。我已经创建并修复了一个查询，因此您将来应该可以少看到一个查询。

我认为这个链接回答了您的问题：一个完全绕过JPA并使用本机的非常好的理由（我越来越倾向于这样做）

Hibernate: select count(*) as col_0_0_ from STUDENTS student0_ where student0_.ID=? and 1=1
Hibernate: select student0_.ID as ID1_2_2_, student0_.FIRST_NAME as FIRST2_2_2_,  educationh1_.STUDENT_ID as STUDENT6_2_4_, educationh1_.ID as ID1_0_4_, educationh1_.ID as  ID1_0_0_, educationh1_.CLASS as CLASS2_0_0_, educationh1_.LEVEL as LEVEL3_0_0_, educationh1_.PREDICTED_END_DATE as PREDICTE4_0_0_, educationh1_.START_DATE as START5_0_0_, educationh1_.STUDENT_ID as STUDENT6_0_0_, educationh1_.TERM as TERM7_0_0_, logs2_.STUDENT_ID as STUDENT3_2_5_, logs2_.ID as ID1_3_5_, logs2_.ID as ID1_3_1_, logs2_.LOG as LOG2_3_1_, logs2_.STUDENT_ID as STUDENT3_3_1_ from STUDENTS student0_ left outer join EDUCATION_HISTORY educationh1_ on student0_.ID=educationh1_.STUDENT_ID left outer join STUDENT_LOG logs2_ on student0_.ID=logs2_.STUDENT_ID where student0_.ID=?
Hibernate: delete from STUDENT_LOG where ID=?
Hibernate: delete from STUDENTS where ID=?