【SpringData&JPA从入门到精通】04-缓存与 JPQL

笔记来源：尚硅谷jpa开发教程全套完整版(初学者零基础入门)

缓存与 JPQL

1、缓存

1.1、一级缓存

测试方法 1

@Test
public void testSecondaryCache(){
    Customer customer1 = entityManager.find(Customer.class, 1);
    Customer customer2 = entityManager.find(Customer.class, 1);
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_0_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?

由于 JPA 的一级缓存，所以实际上只发送了一条 SQL

测试方法 2

@Test
public void testSecondaryCache(){
    Customer customer1 = entityManager.find(Customer.class, 1);

    entityTransaction.commit();
    entityManager.close();

    entityManager = entityManagerFactory.createEntityManager();
    entityTransaction = entityManager.getTransaction();
    entityTransaction.begin();

    Customer customer2 = entityManager.find(Customer.class, 1);
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_0_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
Hibernate: 
    select
        customer0_.id as id1_2_0_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?

这次由于 entityManager 是重新获取的，一级缓存中的内容已经被清理掉了，所以发送了两条 SQL

而 二级缓存 的意义就在于可以跨 JPA 中的 EntityManager，是上述方法可以是发送一条 SQL

1.2、二级缓存

在使用二级缓存前需要做以下准备工作

pom.xml 中添加 二级缓存 相关依赖

<!-- 二级缓存相关依赖 -->
<dependency>
    <groupId>net.sf.ehcache</groupId>
    <artifactId>ehcache-core</artifactId>
    <version>2.4.3</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-ehcache</artifactId>
    <version>4.2.4.Final</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.6.1</version>
</dependency>

persistence.xml 中添加 二级缓存 相关配置

<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
    <persistence-unit name="jpa-1" transaction-type="RESOURCE_LOCAL">
        <!--略...-->
        <!--配置二级缓存策略
            ALL：所有的实体类都被缓存
            NONE：所有的实体类都不被缓存
            ENABLE_SELECTIVE：标识 @Cacheable(true) 注解的实体类将被缓存
            DISABLE_SELECTIVE：除标识 @Cacheable(false) 注解以外的所有实体类都将被缓存
            UNSPECIFIED：默认值，JPA 产品默认值将被使用
        -->
        <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode>
        <properties>
            <!--略...-->
            <!--二级缓存相关-->
            <property name="hibernate.cache.use_second_level_cache" value="true"/>
            <property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.EhcacheRegionFactory"/>
            <property name="hibernate.cache.use_query_cache" value="true"/>
        </properties>
    </persistence-unit>
</persistence>

Customer.java 中添加 二级缓存 相关注解

@Cacheable(value = true)
@Entity
@Table(name = "JPA_CUSTOMERS")
public class Customer {
    // ...
}

再次运行上述代码，查看日志信息

Hibernate: 
    select
        customer0_.id as id1_2_0_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?

2、JPQL

2.1、JPQL 语言

JPQL 语言，即 Java Persistence Query language 的简称
JPQL 是一种和 SQL 非常类似的中间性和对象化查询语言，它最终会被编译成针对不同底层数据库的 SQL 查询，从而屏蔽不同数据库的差异
JPQL 语言的语句可以是 select 语句、update 语句或 delete 语句，它们都通过 Query 接口封装执行

2.2、Query 接口

Query 接口封装了执行数据库查询的相关方法调用 EntityManager 的 createQuery、createNamedQuery 及 createNativeQuery 方法可以获得查询对象，进而可调用 Query 接口的相关方法来执行查询操作

Query 接口的主要方法

int executeUpdate() 用于执行 update 或 delete 语句
List getResultList() 用于执行 select 语句并返回结果集实体列表
Object getsingleResult() 用于执行只返回单个结果实体的 select 语句
Query setFirstResult(int startPosition) 用于设置从哪个实体记录开始返回查询结果
Query setMaxResults(int maxResult) 用于设置返回结果实体的最大数。与 setFirstResult 结合使用可实现分页查询
Query setFlushMode(FlushModeType flushMode) 设置查询对象的 Flush 模式。参数可以取 2 个枚举值
- FlushModeType.AUTO 为自动更新数据库记录
- FlushModeType.COMMMIT 为直到提交事务时才更新数据库记录
setHint(String hintName, Object value) 设置与查询对象相关的特定供应商参数或提示信息。参数名及其取值需要参考特定 JPA 实现库提供商的文档。如果第二个参数无效将抛出 IllegalArgumentException 异常
setParameter(int position, Object value) 为查询语句的指定位置参数赋值。position 指定参数序号，value 为赋给参数的值
setParameter(int position, Date d, TemporalType type) 为查询语句的指定位置参数赋 Date 值。position 指定参数序号，value 为赋给参数的值，type 取 TemporalType 的枚举常量，包括 DATE、TIME 及 TIMESTAMP 三个，用于将 Java 的 Date 型值临时转换为数据库支持的日期时间类型（java.sql.Date、iava.sql.Time 及 java.sql.Timestamp）

2.3、select 语句

select 语句用于执行查询。其语法可表示为

select clause form_clause
	[where_clause]
	[groupby_clause]
	[having_clause]
	[orderby_clause]

2.4、from 子句

from 子句是查询语句的必选子句

select 用来指定查询返回的结果实体或实体的某些属性
from 子句声明查询源实体类，并指定标识符变量（相当于 SQL 表的别名）。如果不希望返回重复实体，可使用关键字 distinct 修饰。select、from 都是 JPQL 的关键字，通常全大写或全小写，建议不要大小写混用

2.5、查询所有实体

查询所有实体的 JPQL 查询字串很简单，例如：select o from Order o 或 select o from Orders as o

关键字 as 可以省去。标识符变量的命名规范与 Java 标识符相同，且区分大小写

调用 EntityManager 的 createQuery() 方法可创建查询对象，接着调用 Query 接囗的 getResultList() 方法就可获得查询结果集。例如：

Query query = entityManager.createQuery("select o from Order o");
List orders = query.getResultList();
Iterator iterator = orders.iterator();
while(iterator.hasNext()){
    //处理 Order
}

2.6、where 子句

where 子句用于指定查询条件，where 跟条件表达式。例：

select o from Orders o where o.id = 1;
select o from Orders o where o.id > 3 and o.confirm = 'true';
select o from Orders o where o.address.streetNumber >= 123;

JPQL 也支持包含参数的查询，例如：

select o from Orders o where o.id = :myId;
select o from Orders o where o.id = :myId and o.customer = :customerName;

注意：参数名前必须冠以冒号(😃，执行查询前须使用 Query.setParameter(name, value) 方法给参数赋值

也可以不使用参数名而使用参数的序号，例如：

select o from Order o where o.id=?1 and o.customer=?2

其中 ?1 代表第一个参数，?2 代表第二个参数。在执行查询之前需要使用重载方法 Query.setParameter(pos，value) 提供参数值

Query query = entityManager.createQuery("select o from Orders o where o.id=?1 and o.customer=?2");
query.setParameter(1, 2);
query.setParameter(2, "John");
List orders = query.getResultList();

where 条件表达式中可用的运算符基本上与 SQL 一致，包括

算术运算符：+、-、*、/、+（正）、-（负）
关系运算符：==、<>、>、>=、<、<=、between...and、like、in、is null 等
逻辑运算符：and、or、not

下面是一些常见查询表达式示例：

# 以下语句查询 Id 介于 100至 200 之间的订单。
select o from Orders o where o.id between 100 and 200 
# 以下语句查询国籍为的 'US'、'CN' 或 'JP' 的客户
select c from Customers c where c.county in("US'，'CN"，"JP")
# 以下语句查询手机号以 139 开头的客户。% 表示任意多个字符序列，包括 0 个。
select c from Customers c where c.phone like '139%'
# 以下语句查询名字包含 4 个字符，且 234 位为 ose 的客户。_ 表示任意单个字符。
select c from Customers c where c.lname like '_ose'
# 以下语句查询电话号码未知的客户。Null 用于测试单值是否为空。
select c from Customers c where c.phone is null
# 以下语句查询尚未输入订单项的订单。empty 用于测试集合是否为空。
select o from Orders o where o.orderltems is empty

2.7、查询部分属性

如果只须查询实体的部分属性而不需要返回整个实体。例如：

select o.id, o.customerName, o.address.streetNumber from Order o order by o.id

执行该查询返回的不再是 Orders 实体集合，而是一个对象数组的集合（Object[]），集合的每个成员为一个对象数组，可通过数组元素访问各个属性

3、JPQL 之 HelloWorld

3.1、where 子句

@Test
public void testAll(){
    String sql = "from Customer c where c.age > ?";
    Query query = entityManager.createQuery(sql);
    // 占位符索引是从 1 开始的
    query.setParameter(1, 1);
    List resultList = query.getResultList();
    System.out.println(resultList.size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.age>?
1

3.2、查询部分属性

测试方法 1

@Test
public void testPart() {
    String sql = "select c.lastName, c.age from Customer c where c.id = ?";
    List resultList = entityManager.createQuery(sql).setParameter(1, 1).getResultList();
    System.out.println(resultList);
}

日志信息

Hibernate: 
    select
        customer0_.LAST_NAME as col_0_0_,
        customer0_.age as col_1_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
[[Ljava.lang.Object;@2e77b8cf]

默认情况下，若只查询部分属性，则将返回 Object[] 类型的结果。或者 Object[] 类型的 List

也可以在实体类中创建对应的构造器，然后在 JPQL 语句中利用对应的构造器返回实体类的对象

@Entity
@Table(name = "JPA_CUSTOMERS")
public class Customer {
    // ...
    public Customer() {
    }

    public Customer(String lastName, int age) {
        this.lastName = lastName;
        this.age = age;
    }
    // ...
}

测试方法 2

@Test
public void testPart2() {
    String sql = "select new Customer(c.lastName, c.age) from Customer c where c.id = ?";
    List resultList = entityManager.createQuery(sql).setParameter(1, 1).getResultList();
    System.out.println(resultList);
}

日志信息

Hibernate: 
    select
        customer0_.LAST_NAME as col_0_0_,
        customer0_.age as col_1_0_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
[Customer{id=null, lastName='Vector', email='null', age=100, birthDay=null, createTime=null}]

可以看到，在 JPQL 中使用 new Customer(c.lastName, c.age) 查询部分属性时，得到的返回类型也变成了 Customer

3.3、createNamedQuery

使用 @NamedQuery 注解定义相关 JPQL 语句

@NamedQuery(name = "testNamedQuery", query = "select c from Customer c where c.id = ?")
@Entity
@Table(name = "JPA_CUSTOMERS")
public class Customer {
    //...
}

测试方法

@Test
public void testNamedQuery(){
    Customer customer = (Customer)entityManager.createNamedQuery("testNamedQuery").setParameter(1, 1).getSingleResult();
    System.out.println(customer);
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
Customer{id=1, lastName='Vector', email='vector@qq.com', age=100, birthDay=2022-05-03, createTime=2022-05-03 17:20:24.0}

3.4、createNativeQuery

@Test
public void testNativeQuery(){
    String sql = "select age from jpa_customers where id=?";
    Object result = entityManager.createNativeQuery(sql).setParameter(1, 1).getSingleResult();
    System.out.println(result);
}

日志信息

Hibernate: 
    select
        age 
    from
        jpa_customers 
    where
        id=?
100

4、JPQL 使用 Hibernate 的查询缓存

注意：需要在 persistence.xml 配置文件中开启缓存相关配置，与 二级缓存 相关配置基本一致，唯一不同的是只需要以下配置

<property name="hibernate.cache.use_second_level_cache" value="true"/>

<property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.EhCacheRegionFactory"/>

<property name="hibernate.cache.use_query_cache" value="true"/>

而 <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode> 和 @Cacheable 就不再需要了

测试方法 1：默认情况下多次查询会发送多条 SQL

@Test
public void testQueryCache(){
    String sql = "select c from Customer c where c.id=?";
    // First Query
    Query query = entityManager.createQuery(sql).setParameter(1, 1);
    List resultList = query.getResultList();
    System.out.println(resultList.size());
    // Second Query
    Query query2 = entityManager.createQuery(sql).setParameter(1, 1);
    List resultList2 = query2.getResultList();
    System.out.println(resultList2.size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
1
Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
1

通过调用 setHint() 方法设置 HINT_CACHEABLE 为 true，即开启查询缓存

@Test
public void testQueryCache(){
    String sql = "select c from Customer c where c.id=?";
    // First Query
    Query query = entityManager.createQuery(sql).setParameter(1, 1).setHint(QueryHints.HINT_CACHEABLE, true);
    List resultList = query.getResultList();
    System.out.println(resultList.size());
    // Second Query
    Query query2 = entityManager.createQuery(sql).setParameter(1, 1).setHint(QueryHints.HINT_CACHEABLE, true);
    List resultList2 = query2.getResultList();
    System.out.println(resultList2.size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
1
1

可以看到，原本的 2 条 SQL 语句只剩下了 1 条

5、JPQL 的 Order By 和 Group By

测试方法 1

@Test
public void testOrderBy(){
    String sql = "select c from Customer c where c.id=? order by c.age desc";
    List resultList = entityManager.createQuery(sql).setParameter(1, 1).getResultList();
    System.out.println(resultList.size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=? 
    order by
        customer0_.age desc
1

测试方法 2

@Test
public void testGroupBy(){
    String sql = "select o.customer from Order o group by o.customer having count(o.id) >= 2";
    List<Order> resultList = entityManager.createQuery(sql).getResultList();
    System.out.println(resultList);
}

日志信息

Hibernate: 
    select
        customer1_.id as id1_2_,
        customer1_.age as age2_2_,
        customer1_.birthDay as birthDay3_2_,
        customer1_.createTime as createTi4_2_,
        customer1_.email as email5_2_,
        customer1_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_ORDER order0_ 
    inner join
        JPA_CUSTOMERS customer1_ 
            on order0_.CUSTOMER_ID=customer1_.id 
    group by
        order0_.CUSTOMER_ID 
    having
        count(order0_.id)>=2
[Customer{id=4, lastName='customer2', email='customer2@qq.com', age=21, birthDay=2022-05-03, createTime=2022-05-03 20:41:55.0}]

6、JPQL 的关联查询

在 JPQL 中，很多时候都是通过在实体类中配置实体关联的类属性来实现隐含的关联（join）查询。例如：

select o from Orders o where o.address.streetNumber = 2000

上述 JPQL 语句编译成以下 SQL 时就会自动包含关联，默认为左关联

在某些情况下可能仍然需要对关联做精确的控制。为此，JPQL 也支持和 SQL 中类似的关联语法。如：

left out join / left join
inner join
left join / inner join fetch

其中，left join 和 left out join 等义，都是允许符合条件的右边表达式中的实体为空

测试方法 1

@Test
public void testLeftOuterJoinFetch() {
    String jpql = "from Customer c where c.id=?";
    Customer customer = (Customer) entityManager.createQuery(jpql).setParameter(1, 4).getSingleResult();
    System.out.println(customer.getLastName());
    System.out.println(customer.getOrders().size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_,
        customer0_.age as age2_2_,
        customer0_.birthDay as birthDay3_2_,
        customer0_.createTime as createTi4_2_,
        customer0_.email as email5_2_,
        customer0_.LAST_NAME as LAST_NAM6_2_ 
    from
        JPA_CUSTOMERS customer0_ 
    where
        customer0_.id=?
customer2
Hibernate: 
    select
        orders0_.CUSTOMER_ID as CUSTOMER3_2_1_,
        orders0_.id as id1_6_1_,
        orders0_.id as id1_6_0_,
        orders0_.CUSTOMER_ID as CUSTOMER3_6_0_,
        orders0_.ORDER_NAME as ORDER_NA2_6_0_ 
    from
        JPA_ORDER orders0_ 
    where
        orders0_.CUSTOMER_ID=?
2

此时发送了 2 条 SQL 语句

测试方法 2

JPQL 的关联查询同 HQL 的关联查询

@Test
public void testLeftOuterJoinFetch() {
    String jpql = "from Customer c left outer join fetch c.orders where c.id=?";
    Customer customer = (Customer) entityManager.createQuery(jpql).setParameter(1, 4).getSingleResult();
    System.out.println(customer.getLastName());
    System.out.println(customer.getOrders().size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_0_,
        orders1_.id as id1_6_1_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_,
        orders1_.CUSTOMER_ID as CUSTOMER3_6_1_,
        orders1_.ORDER_NAME as ORDER_NA2_6_1_,
        orders1_.CUSTOMER_ID as CUSTOMER3_2_0__,
        orders1_.id as id1_6_0__ 
    from
        JPA_CUSTOMERS customer0_ 
    left outer join
        JPA_ORDER orders1_ 
            on customer0_.id=orders1_.CUSTOMER_ID 
    where
        customer0_.id=?
customer2
2

此时只发送了 1 条 SQL 语句

测试方法 3

如果去掉 fetch，即使用 left outer join，结果又会怎样呢？

@Test
public void testLeftOuterJoinFetch() {
    String jpql = "from Customer c left outer join c.orders where c.id=?";
    Customer customer = (Customer) entityManager.createQuery(jpql).setParameter(1, 4).getSingleResult();
    System.out.println(customer.getLastName());
    System.out.println(customer.getOrders().size());
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_0_,
        orders1_.id as id1_6_1_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_,
        orders1_.CUSTOMER_ID as CUSTOMER3_6_1_,
        orders1_.ORDER_NAME as ORDER_NA2_6_1_ 
    from
        JPA_CUSTOMERS customer0_ 
    left outer join
        JPA_ORDER orders1_ 
            on customer0_.id=orders1_.CUSTOMER_ID 
    where
        customer0_.id=?
五月 19, 2022 9:53:05 下午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH000030: Cleaning up connection pool [jdbc:mysql:///jpa]

javax.persistence.NonUniqueResultException: result returns more than one elements
<1 internal line>
	at helloworld.JPQLTest.testLeftOuterJoinFetch(JPQLTest.java:113) <1 internal line>

抛出了 NonUniqueResultException 异常，错误提示信息：结果不止一条

测试方法 4

既然结果不止 1 条，那我们就用 getResultList() 方法来接收结果集

@Test
public void testLeftOuterJoinFetch() {
    String jpql = "from Customer c left outer join c.orders where c.id=?";
    List<Object[]> resultList = entityManager.createQuery(jpql).setParameter(1, 4).getResultList();
    System.out.println(resultList);
}

日志信息

Hibernate: 
    select
        customer0_.id as id1_2_0_,
        orders1_.id as id1_6_1_,
        customer0_.age as age2_2_0_,
        customer0_.birthDay as birthDay3_2_0_,
        customer0_.createTime as createTi4_2_0_,
        customer0_.email as email5_2_0_,
        customer0_.LAST_NAME as LAST_NAM6_2_0_,
        orders1_.CUSTOMER_ID as CUSTOMER3_6_1_,
        orders1_.ORDER_NAME as ORDER_NA2_6_1_ 
    from
        JPA_CUSTOMERS customer0_ 
    left outer join
        JPA_ORDER orders1_ 
            on customer0_.id=orders1_.CUSTOMER_ID 
    where
        customer0_.id=?
[[Ljava.lang.Object;@72c927f1, [Ljava.lang.Object;@1ac85b0c]

通过上述几个测试方法可知，left outer join fetch 要比 left outer join 的结果集更人性化，我们处理起来也更加友好

7、JPQL 的子查询

JPQL 也支持子查询，在 where 或 having 子句中可以包含另一个查询。当子查询返回多于 1 个结果集时，它常出现在 any、all、exists 表达式中用于集合匹配查询。它们的用法与 SQL 语句基本相同

测试方法

@Test
public void testSubQuery() {
    // 查询所有 Customer 的 lastName 为 customer1 的 Order
    String jpql = "select o from Order o where o.customer = (select c from Customer c where c.lastName = ?)";
    List<Order> resultList = entityManager.createQuery(jpql).setParameter(1, "customer1").getResultList();
    System.out.println(resultList);
}

日志信息

Hibernate: 
    select
        order0_.id as id1_6_,
        order0_.CUSTOMER_ID as CUSTOMER3_6_,
        order0_.ORDER_NAME as ORDER_NA2_6_ 
    from
        JPA_ORDER order0_ 
    where
        order0_.CUSTOMER_ID=(
            select
                customer1_.id 
            from
                JPA_CUSTOMERS customer1_ 
            where
                customer1_.LAST_NAME=?
        )
[Order{id=2, orderName='Customer1-Order2'}]

8、JPQL 的内建函数

JPQL 提供了以下一些内建函数，包括字符串处理函数、算术函数和日期函数

为方便测试，提取一个统一的方法

private void testFunction(String jpql) {
    List<String> resultList = entityManager.createQuery(jpql).getResultList();
    System.out.println(resultList);
}

字符串处理函数

concat(String s1, String s2)：字符串合并/连接函数
substring(String s, int start, int length)：取字串函数
trim([leading|trailing|both,] [char c,] String s)：从字符串中去掉首/尾指定的字符或空格
lower(String s)：将字符串转换成小写形式
upper(String s)：将字符串转换成大写形式
length(String s)：求字符串的长度
locate(String s1，String s2[, int start])：从第一个字符串中查找第二个字符串（子串）出现的位置。若未找到则返回 0

测试方法 1

@Test
public void testConcat() {
    testFunction("select concat(c.lastName, '<' , c.email, '>') from Customer c");
}

日志信息

[Vector<vector@qq.com>, Vector<vector@qq.com>, customer1<customer1@qq.com>, customer2<customer2@qq.com>]

测试方法 2

@Test
public void testSubstring() {
    testFunction("select substring(c.email, 6) from Customer c");
}

日志信息

[r@qq.com, r@qq.com, mer1@qq.com, mer2@qq.com]

测试方法 3

@Test
public void testLength() {
    testFunction("select length(c.email) from Customer c");
}

日志信息

[13, 13, 16, 16]

测试方法 4

@Test
public void testUpper() {
    testFunction("select upper(c.email) from Customer c");
}

日志信息

[VECTOR@QQ.COM, VECTOR@QQ.COM, CUSTOMER1@QQ.COM, CUSTOMER2@QQ.COM]

测试方法 5

@Test
public void testLower() {
    testFunction("select lower(c.email) from Customer c");
}

日志信息

[vector@qq.com, vector@qq.com, customer1@qq.com, customer2@qq.com]

算术函数

主要有 abs、mod、sqrt、size 等。size 用于求集合的元素个数

日期函数

主要为三个，即 current_date、current_time、current_timestamp，它们不需要参数，返回服务器上的当前日期、时间和时戳

9、JPQL 的 update

update 语句用于执行数据更新操作。主要用于针对单个实体类的批量更新

以下语句将帐户余额不足万元的客户状态设置为未偿付：

update Customers c set c.status='未偿付' where c.balance < 10000

测试方法

@Test
public void testUpdate() {
    String jpql = "update Customer c set c.lastName=? where c.id=?";
    Query query = entityManager.createQuery(jpql).setParameter(1, "customer-update").setParameter(2, 3);
    query.executeUpdate();
}

日志信息

Hibernate: 
    update
        JPA_CUSTOMERS 
    set
        LAST_NAME=? 
    where
        id=?

查询数据表 JPA_CUSTOMERS

10、JPQL 的 delete

delete 语句用于执行数据更新操作

以下语句删除不活跃的、没有订单的客户：

delete from Customers c where c.status='inactive' and c.orders is empty

测试方法

@Test
public void testDelete() {
    String jpql = "delete from Customer c where c.id=?";
    Query query = entityManager.createQuery(jpql).setParameter(1, 1);
    query.executeUpdate();
}

日志信息

Hibernate: 
    delete 
    from
        JPA_CUSTOMERS 
    where
        id=?

查询数据表 JPA_CUSTOMERS

总结

本节重点掌握 JPQL 相关内容

Query 接口：获取查询对象的三种方法、执行查询操作的相关方法
查询语句：查询所有实体和部分属性的语句写法、关联查询、子查询
内建函数：字符串处理函数、算术函数、日期函数

附上导图，仅供参考

缓存与JPQL

posted @ 2022-05-19 23:14 VectorX 阅读(267) 评论(0) 编辑收藏举报

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VectorX

【SpringData&JPA从入门到精通】04-缓存与 JPQL

缓存与 JPQL

1、缓存

1.1、一级缓存

1.2、二级缓存

2、JPQL

2.1、JPQL 语言

2.2、Query 接口

2.3、select 语句

2.4、from 子句

2.5、查询所有实体

2.6、where 子句

2.7、查询部分属性

3、JPQL 之 HelloWorld

3.1、where 子句

3.2、查询部分属性

3.3、createNamedQuery

3.4、createNativeQuery

4、JPQL 使用 Hibernate 的查询缓存

5、JPQL 的 Order By 和 Group By

6、JPQL 的关联查询

7、JPQL 的子查询

8、JPQL 的内建函数

字符串处理函数

算术函数

日期函数

9、JPQL 的 update

10、JPQL 的 delete

总结

公告