Hibernate一對一關聯實用介紹
#0
書和文檔上寫的都不是特清楚的。自己記下來。
#1 Using a PK association
#1.1 POJO with XDolclet annotation
public class Customer {
/**
* @return Returns the shoppingCart.
* @hibernate.many-to-one cascade="delete" column="shopping_cart_id"
* unique="true" foreign-key="FK_SHOPPING_CART__CUSTOMER"
*/
public ShoppingCart getShoppingCart() {
return shoppingCart;
}
}
public class ShoppingCart {
/**
* @return Returns the customer.
* @hibernate.one-to-one property-ref="shoppingCart"
*/
public Customer getCustomer() {
return customer;
}
}
property-ref="shoppingCart" 告訴Hibernate ShoppingCart#customer和Customer#shoppingCart是反向的關系。所以Hibernate知道如何從ShoppingCart#getCustomer中檢索到相應的customer對象。取出某個Customer對象時，Hibernate會生成DEBUG SQL:324 - 3中的SQL語句。
#1.2 HBM
Customer.hbm.xml
<many-to-one
name="shoppingCart"
class="ShoppingCart"
cascade="delete"
outer-join="auto"
foreign-key="FK_SHOPPING_CART__CUSTOMER"
column="shopping_cart_id"
/>
ShoppingCart.hbm.xml
<one-to-one
name="customer"
class="Customer"
cascade="none"
outer-join="auto"
constrained="false"
property-ref="shoppingCart"
/>
#1.3 SCHEMA SQL
create table CUSTOMER (
ID bigint generated by default as identity (start with 1),
SHOPPING_CART_ID bigint,
primary key (ID)
)
create table SHOPPING_CART (
ID bigint generated by default as identity (start with 1)
primary key (ID)
)
alter table CUSTOMER
add constraint FK_SHOPPING_CART__CUSTOMER
foreign key (SHOPPING_CART_ID)
references SHOPPING_CART
#1.4 Query SQL
DEBUG SQL:324 - 1
select customer0_.ID as ID, customer0_.SHOPPING_CART_ID as SHOPPING2_3_, customer0_.USERNAME as USERNAME3_, customer0_.PWD as PWD3_
from CUSTOMER customer0_
where customer0_.USERNAME=? and customer0_.PWD=?
DEBUG SQL:324 - 2
select shoppingca0_.ID as ID0_, shoppingca0_.TOTAL as TOTAL8_0_
from SHOPPING_CART shoppingca0_
where shoppingca0_.ID=?
DEBUG SQL:324 - 3
select customer0_.ID as ID1_, customer0_.SHOPPING_CART_ID as SHOPPING2_3_1_, customer0_.USERNAME as USERNAME3_1_, customer0_.PWD as PWD3_1_, shoppingca1_.ID as ID0_, shoppingca1_.TOTAL as TOTAL8_0_
from
CUSTOMER customer0_
left outer join
SHOPPING_CART shoppingca1_
on customer0_.SHOPPING_CART_ID=shoppingca1_.ID
where customer0_.SHOPPING_CART_ID=?
#2 Using a FK association
#2.1 POJO with XDolclet annotation
public class Customer {
/**
* @return Returns the shoppingCart.
* @hibernate.one-to-one cascade="delete"
*/
public ShoppingCart getShoppingCart() {
return shoppingCart;
}
}
public class ShoppingCart {
/**
* @return Returns the id.
* @hibernate.id generator-class="foreign"
* @hibernate.generator-param name="property" value="customer"
*/
public Long getId() {
return id();
}
/**
* @return Returns the customer.
* @hibernate.one-to-one constrained="true" foreign-key="FK_CUSTOMER__SHOPPING_CART"
*/
public Customer getCustomer() {
return customer;
}
}
constrained="true" 告訴Hibernate ShoppingCart的PK還應該是一個FK，這個FK引用Customer的PK。還需要多做一點工作，聲明ShoppingCart的PK生成策略是foreign，對應ShoppingCart#customer。這和上面一句話不是一個意思嘛，FT~~
#2.2 HBM
Customer.hbm.xml
<one-to-one
name="shoppingCart"
class="ShoppingCart"
cascade="delete"
outer-join="auto"
constrained="false"
/>
ShoppingCart.hbm.xml
<id
name="id"
column="id"
type="java.lang.Long"
>
<generator class="foreign">
<param name="property">customer</param>
</generator>
</id>
<one-to-one
name="customer"
class="Customer"
cascade="none"
outer-join="auto"
constrained="true"
/>
#2.3 SCHEMA SQL
create table CUSTOMER (
ID bigint generated by default as identity (start with 1),
primary key (ID)
)
create table SHOPPING_CART (
ID bigint not null,
TOTAL integer,
primary key (ID)
)
alter table SHOPPING_CART
add constraint FK_CUSTOMER__SHOPPING_CART
foreign key (ID)
references CUSTOMER
#2.4 Query SQL
DEBUG SQL:324 -
select customer0_.ID as ID, customer0_.USERNAME as USERNAME3_, customer0_.PWD as PWD3_
from CUSTOMER customer0_
where customer0_.USERNAME=? and customer0_.PWD=?
DEBUG SQL:324 -
select shoppingca0_.ID as ID0_, shoppingca0_.TOTAL as TOTAL8_0_
from SHOPPING_CART shoppingca0_
where shoppingca0_.ID=?
這個“真正”的one-to-one的好處是少條關聯SQL語句，看到了嗎？