java Java的：休眠：查询：HQL

Posted 2021-05-08

HQL是完全面向对象的查询语言，因此可以支持继承和多态等特征。

## 查询示例
HQL查询依赖于Query类，每个Query实例对应一个查询对象，使用HQL查询按如下步骤进行：
1. 获取Hibernate Session对象；
2. 编写HQL语句；
3. 以HQL语句作为参数，调用Session的createQuery方法创建查询对象；
4. 如果HQL语句包含参数，调用Query的setXxx方法为参数赋值；
5. 调用Query对象的list等方法遍历查询结果。

```java
private void findPersons() throws Exception{
  Session sess = HibernateUtil.currentSession();
  //开始事务
  Transaction tx = sess.beginTransaction();
  //以HQL语句创建Query对象
  List p1 = sess.createQuery("from Person p where o.myEvents.title = :eventTitle")
    //执行setString方法为HQL语句的参数赋值
    .setString("eventTitle", "很普通事情")
    //Query调用list方法访问查询的全部实例
    .list();
  //遍历查询的全部结果
  for(Iterator pit = p1.iterator(); pit.haxNext();){
    Person p = (Person)pit.next();
    System.out.println(p.getName());
  }
  //提交事务
  tx.commit();
  HibernateUtil.closeSession();
}


private void findPersonByHappenDate() throws Exception{
  Session sess = HibernateUtil.currentSession();
  Transaction tx = sess.beginTransaction();
  //解析出Date对象
  SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
  Date start = sdf.parse("2007-11-27");
  System.out.println("系统开始通过日期查找人" + start);
  //通过Session的createQuery方法创建Query对象
  List pl = sess.createQuery(
      "from Person p where p.myEvents.happenDate between :firstDate and :endDate")
      //设置参数
      .setDate("firstDate", start)
      .setDate("endDate", new Date())
      //返回结果集
      .list();
  //遍历结果集
  for(Iterator pit = pl.iterator(); pit.hasNext();){
    Person p = (Person)pit.next();
    System.out.println(p.getName());
  }
  tx.commit();
  HibernateUtil.closeSession();
}


// 调用命名查询的示例代码如下：
private void findByNamedQuery() throws Exception {
  Session session = HibernateUtil.currentSession();
  Transaction tx = session.beginTransaction();
  System.out.println("执行命名查询");
  //调用命名查询
  List pl = sess.getNamedQuery("myNamedQuery")
      //为参数赋值
      .setInteger(0, 20)
      //返回全部结果
      .list();
  //遍历结果集
  for (Integer pit = pl.iterator(); pit.hasNext(); ){
    Person p = (Person)pit.next();
    System.out.println(p.getName());
  }
  tx.commit();
  HibernateUtil.closeSession();
}
```

## 语法

#### 1. from 子句

from Person - 表明从Person持久化类中选出全部的实例

推荐与as连用

```sql
from Person as p
```

#### 2. select 子句
```sql
select p.name from Person as p

select p.name.firstName from Person as p

select new list(p.name, p.address) from Person as p

select new ClassTest(p.name, p.address) from Person as p (有前提)

select p.name as personName from Person as p

select new map(p.name as personName) from Person as p (与new map()结合更普遍)
```
#### 3. 聚集函数

avg, count, max, min, sum
```sql
select count(*) from Person

select max(p.age) from Person as p

select p.name || "" || p.address from Person as p
```
#### 4. 多态查询
```sql
from Person as p

from java.lang.Object o

from Named as n
```
#### 5. where子句
```sql
from Person where name like "tom%"

from Person as p where p.name like "tom%"

from Cat cat where cat.mate.name like "kit%"

select * from cat_table as table1 cat_table as table2
where table1.mate = table2.id
  and table1.name like "kit%"

from Foo foo where foo.bar.baz.customer.address.city like "fuzhou%"

from Cat cat, Cat rival where cat.mate = rival.mate

select cat, mate from Cat cat, Cat mate where cat.mate = mate

from Cat as cat where cat.id = 123

from Cat as cat where cat.mate.id = 69

from Person as person
where person.id.country = ''AU''
  and person.id.medicareNumber = 123456

from Account as account
where account.owner.id.country = ''AU''
  and account.owner.id.medicareNumber = 123456

from Cat cat where cat.class = DomesticCat

from Account as a where a.person.name.firstName like "dd%" // 正确

from Account as a where a.person.name like "dd%" // 错误
```
#### 6. 表达式
```sql
from DomesticCat cat where cat.name between ''A'' and ''B''

from DomesticCat cat where cat.name in (''Foo'', ''Bar'', ''Baz'')

from DomesticCat cat where cat.name not between ''A'' and ''B''

from DomesticCat cat where cat.name not in (''Foo'', ''Bar'', ''Baz'')

from DomesticCat cat where cat.name is null

from Person as p where p.address is not null

// Booleans can be easily used in expressions by declaring HQL query substitutions in Hibernate configuration:
// <property name="hibernate.query.substitutions">true 1, false 0</property>
from Cat cat where cat.alive = true

from Cat cat where cat.kittens.size > 0

from Cat cat where size(cat.kittens) > 0

from Calendar cal where maxelement(cal.holidays) > current date

from Order order where maxindex(order.items) > 100

from Order order where minelement(order.items) > 10000

//操作集合元素
select mother from Cat as mother, Cat as kit
where kit in elements(foo.kittens)

//p的name属性等于集合中某个元素的name属性

select p from NameList list, Person p
where p.name = some elements(list.names)

//操作集合元素
from Cat cat where exists elements(cat.kittens)
from Player p where 3 > all elements(p.scores)
from Show show where ''fizard'' in indices(show.acts)

//items是有序集合属性，items[0]代表第一个元素

from Order order where order.items[0].id = 1234

//holidays是map集合属性，holidays[national day]是代表其中第一个元素
select person from Person person, Calendar calendar
where calendar.holidays[''national day''] = person.birthDay
  and person.nationality.calendar = calendar

//下面同时使用list集合和map集合属性
select item from Item item, Order order
where order.items[order.deliveredItemIndices[0]] = item
  and order.id = 11

select item from Item item, Order order
where order.items[maxindex(order.items)] = item
  and order.id = 11

select item from Item item, Order order
where order.items[size(order.items) - 1] = item

select cust
from Product prod, Store store
inner join store.customers cust
where prod.name = ''widget''
  and store.location.name in [''Melbourne'', ''Sydney'']
  and prod = all elements(cust.currentOrder.lineItems)

SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_order
FROM customers cust, stores store, locations loc, store_customers sc, product prod
WHERE prod.name = ''widget''
  AND store.loc_id = loc.id
  AND loc.name IN (''Melbourne'', ''Sydney'')
  AND sc.store_id = store.id
  AND sc.cust_id = cust.id
  AND prod.id = ALL(
    SELECT item.prod_id
    FROM line_items item, orders o
    WHERE item.order_id = o.id
    AND cust.current_order = o.id
  )
```
#### 7.order by子句
```sql
from Person as p order by p.name, p.age
from Person as p order by p.name asc, p.age desc
```
#### 8.group by子句
```sql
select cat.color, sum(cat.weight), count(cat)
from Cat cat
group by cat.color

//select后出现的id处出现在group by之后，而name属性则出现在聚集函数中
select foo.id, avg(name), max(name)
from Foo foo join foo.names name
group by foo.id

select cat.color, sum(cat.weight), count(cat)
from Cat cat
group by cat.color
having cat.color in (eg.Color.TABBY, eg.Color.BLACK)

select cat
from Cat cat
join cat.kittens kitten
group by cat
having avg(kitten.weight) > 100
order by count(kitten) asc, sum(kitten.weight) desc
```
#### 9. 子查询
```sql
from Cat as fatcat
where fatcat.weight > (select avg(cat.weight) from DomesticCat cat)

from Cat as cat
where not (cat.name, cat.color) in (
select cat.name, cat.color from DomesticCat cat
)

@Query("SELECT u FROM DlrmUser u WHERE u.id NOT IN" +
      " (SELECT access.grantedTo.id FROM UserWaterAccountAccess access where access.account.id = ?1)")
List<DlrmUser> listUsersNotGrantedToThisAccount(Long accountId);
```
#### 10. fetch关键字
```sql
from Person as p join p.scores

from Document fetch all properties order by name
from Document doc fetch all properties where lower(doc.name) like ''%cat%''
```
#### 11. 命名查询
```xml
<!--定义命名查询-->
<query name="myNamedQuery">
<!--此处确定命名查询的HQL语句-->
from Person as p where p.age > ?
</query>
```

@Repository
public interface FooRepository extends BaseRepository<Foo> {

  // ...

	@Query(nativeQuery=true, value="SELECT COUNT(*) FROM foo f WHERE f.number NOT IN (SELECT b.number from bar b)")
	long countAvailableFoo();
	
	// ...
}

/* Solution 1 - Implicitly handled by entity manager (or session) in a transactional context */
@Service
public class DeviceServiceImpl implements DeviceService {
  ...

  @Transactional // In a transactional context, the entity manager will automatically maintain the graph
  public Device findByLicenceNumberForProcessingStatusData(String number) {
      Device device = repo.findByNumberFetchAllOrderByZoneNumberAsc(number);
      programService.findByDeviceFetchTimings(device);
      return device;
  }

  ...

}

@Query("SELECT t "
        + " FROM Account a "
        + " JOIN a.lineItems items "
        + " JOIN items.transaction t "
        + " WHERE a.id = :accountId ORDER BY t.createdTs DESC, items.amount ASC")
List<Transaction> findAllByAccountIdOrderByCreatedTsDesc(@Param("accountId") Long accountId);