Spring JPA 生成 SELECT 查询现有拥有实体的新关联实体

Question

I have an owning entity class with some associated entities, eg

@Entity
public class Parent {
    @Id
    @GeneratedValue
    private UUID id;
    @OneToMany(mappedBy = "parentId", cascade = CascadeType.ALL)
    List<Child> children;
    ...
}

@Entity
public class Child {
    @Id
    @GeneratedValue
    private UUID id;
    private UUID parentId;
    ...
}

I am using Spring Boot Starter Data JPA. I traced the code to the SimpleJpaRepository class, I noticed that on calling save(parent) , it checks if isNew() returns true, Spring will call persist() ; otherwise it calls merge() . This makes total sense, as persist() will generate only an INSERT, while merge() will generate a SELECT (if it hasn't done before) and then followed by an INSERT if the SELECT returns nothing; otherwise an UPDATE.

The above works well when saving a new Parent with new Child , only INSERTs are generated without any SELECT.

However, my problem is, when creating some new Child and adding them to an existing Parent , then on saving the parent, somehow I noticed Spring JPA is still generating an extra SELECT for each of these new Child entities before the INSERTs, which I found unnecessary.

Is there a way to avoid these SELECT queries?

---

Further investigation I found that if I leave the id of the Child null (ie let it auto generates a new id), then only INSERT is generated. However, if I manually assign an id to a Child , then a SELECT will be generated before an INSERT. Is there a way I can assign id to Child while avoiding the extra SELECT?

Answer 1

On the basis of your code i think because of .netoMany mapping and you did't provide cascade type then it not happen select query running two times provide more information full code of Entity classes properties file