[英]Eager fetch performs left join in hibernate but fires seperate sql queries in springboot/JPA
我看到很多帖子,其中Eager fetch在hibernate中執行子表父表的左連接。 但是當我使用springboot時,hibernate會激活單獨的sql查詢 - 意味着一個選擇父表的查詢和一個子表的選擇查詢。 為什么會有區別? springboot中是否有任何升級或者我做錯了什么?
以下是我使用的實體:
訂單實體:
@Entity
@Table(name="Ordertable", schema="cf_2583f365_c3c6_499a_a60d_138e7e7023eb")
public class Order {
@Id
@Column(name = "ORDER_ID")
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int orderId;
@Column(name = "DAT_SRC_ID")
private String dataSourceId;
@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name = "ORDER_CUSTOMER_ID", referencedColumnName = "CUSTOMER_ID")
private Customer customer;
}
客戶實體:
@Entity
@Table(name="Customer", schema="cf_2583f365_c3c6_499a_a60d_138e7e7023eb")
public class Customer {
@Id
@Column(name = "CUSTOMER_ID")
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long customerId;
@Column(name = "CUSTOMER_NAME")
private String customer_name;
@Column(name = "CUSTOMER_address_id")
private int customer_address_id;
@Column(name = "DAT_SRC_ID")
private String dataSourceId;
@OneToMany(fetch=FetchType.EAGER)
@JoinColumn(name = "ORDER_CUSTOMER_ID", referencedColumnName = "CUSTOMER_ID")
private List<Order> order;
}
控制器:
@RequestMapping(value="/getByCustid/{id}", method=RequestMethod.GET,produces=MediaType.APPLICATION_JSON_VALUE)
public Customer getByCustid (@PathVariable Long id) {
Customer s1 = customerRepository.findByCustomerId(id);
return s1;
}
庫:
public interface CustomerRepository extends JpaRepository<Customer,Long> {
public Customer findByCustomerId(Long customerId);
}
以下是要執行的查詢:
select
customer0_.CUSTOMER_ID as CUSTOMER1_0_,
customer0_.CUSTOMER_address_id as CUSTOMER2_0_,
customer0_.CUSTOMER_NAME as CUSTOMER3_0_,
customer0_.DAT_SRC_ID as DAT_SRC_4_0_
from
Customer customer0_
where
customer0_.CUSTOMER_ID=?
select
order0_.ORDER_CUSTOMER_ID as ORDER_CU3_5_0_,
order0_.ORDER_ID as ORDER_ID1_5_0_,
order0_.ORDER_ID as ORDER_ID1_5_1_,
order0_.ORDER_CUSTOMER_ID as ORDER_CU3_5_1_,
order0_.DAT_SRC_ID as DAT_SRC_2_5_1_
from
Ordertable order0_
where
order0_.ORDER_CUSTOMER_ID=?
編輯:這與@Fetch(FetchMode.JOIN)有關 - 鏈接: JPA eager fetch不加入
Hibernate:Hibernate為Fetch模式Eager做出的多個選擇查詢
要檢查FetchMode.JOIN是否有效,我在實體中添加了FetchMode.JOIN,如下所示,但仍然沒有成功使用Join Query:
客戶實體:
@Entity
@Table(name="Customer", schema="cf_2583f365_c3c6_499a_a60d_138e7e7023eb")
public class Customer {
@OneToMany(fetch=FetchType.EAGER)
@JoinColumn(name = "ORDER_CUSTOMER_ID", referencedColumnName = "CUSTOMER_ID")
@Fetch(FetchMode.JOIN)
private List<Order> order;
}
訂單實體:
@Entity
@Table(name="Ordertable", schema="cf_2583f365_c3c6_499a_a60d_138e7e7023eb")
public class Order {
@JsonIgnore
@ManyToOne()
@JoinColumn(name = "ORDER_CUSTOMER_ID", referencedColumnName = "CUSTOMER_ID")
@Fetch(FetchMode.JOIN)
private Customer customer;
}
findByCustomerId
實際上將基於該方法生成查詢,而不是使用em.find
。 它將創建SELECT c FROM Customer c WHERE c.customerId=:customerId
。 之后它會注意到獲取策略並獲得所需的引用。 這也在這里解釋。 查詢將完全按照您的指示進行操作。
如果你想急切地加載引用,你需要自己編寫查詢來自SELECT c FROM Customer c JOIN FETCH c.orders o WHERE c.customerId=:customerId
,這將自動檢索訂單。
但是, customerId
實際上是實體的主鍵或findById
,因此您實際上應該使用findById
或findOne
方法(取決於您的Spring Data JPA版本)。 這將使用EntityManager.find
,它應該考慮映射信息並創建適當的查詢。
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