定義
- Hibernate Query Language, Hiberhate查詢語(yǔ)言
- HQL是面向?qū)ο蟮牟樵冋Z(yǔ)言
- HQL語(yǔ)句形式
Paste_Image.png - 點(diǎn)擊查看練習(xí)代碼
一．org.hibernate.Query接口
-
Query接口定義有執(zhí)行查詢的方法
Paste_Image.png Session的createQuery()方法創(chuàng)建Query實(shí)例
createQuery()方法包含一個(gè)HQL語(yǔ)句參數(shù)， createQuery(hql)
Query接口的list()方法執(zhí)行HQL查詢
list()方法返回結(jié)果數(shù)據(jù)類型為java.util.List, list接合中存放符合查詢條件的持久化對(duì)象；
/**
* 查詢班級(jí)信息
*/
@Test
public void testGrade() {
//定義hql語(yǔ)句，Grade類不需要寫全限定名：entity.Grade, 默認(rèn)情況會(huì)auto-import
String hql = "from Grade";
Query query = session.createQuery(hql);
List<Grade> res = query.list();
for (Grade grade : res) {
//只輸出班級(jí)名稱，則hibernate只查詢grade表，不產(chǎn)生關(guān)聯(lián)查詢
System.out.println(grade.getGname());
//當(dāng)輸出班級(jí)包含的學(xué)生屬性時(shí)候，hibernate會(huì)根據(jù)關(guān)聯(lián)關(guān)系查詢student2表數(shù)據(jù)
System.out.println(grade.getStudent2());
}
}
二．from子句中持久化類的引用
- 不需要引入持久化類的全限定名，直接引入類名, 比如要查詢
- auto-import(自動(dòng)引入)缺省情況
三．select子句返回選擇屬性的格式
- 以對(duì)象數(shù)組Object[]形式返回選擇的屬性
/**
* 以O(shè)bject數(shù)組形式返回查詢屬性
*/
@Test
public void testSelectColumnObjectArray()
{
/*
//使用select查詢班級(jí)id和名稱，返回對(duì)象數(shù)組
String hql = "SELECT g.gid, g.gname FROM Grade AS g";
Query query = session.createQuery(hql);
List<Object[]> list = query.list();
for (Object[] objects : list) {
System.out.println("id = " + objects[0] + "name: " + objects[1]);
} */
//當(dāng)只查詢一個(gè)屬性的時(shí)候，返回的是對(duì)象，而不是對(duì)象數(shù)組
String hql1 = "SELECT g.gname FROM Grade AS g";
Query query1 = session.createQuery(hql1);
List<Object> list1 = query1.list();
System.out.println("name = " + list1.get(0));
}
- 以List形式放回選擇的屬性
/**
* 以List集合形式返回查詢屬性, select語(yǔ)句中指定new list
*/
@Test
public void testSelectColumnList()
{
//以List集合形式返回查詢屬性 SELECT new list(g.gid, g.gname)
String hql = "SELECT new list(g.gid, g.gname) FROM Grade AS g";
Query query = session.createQuery(hql);
List<List> lists = query.list();
for (List list : lists) {
System.out.println("id = " + list.get(0) + "name = " + list.get(1));
}
}
- 以map形式返回選擇的屬性
/**
* 以Map集合形式返回查詢屬性, select語(yǔ)句中指定new map
* 如果指定屬性未定義AS別名，在獲取的時(shí)候要使用get("0")字符串下標(biāo)方式獲取
* 如果指定屬性定義AS別名，在獲取的時(shí)候可以使用屬性別名作為key查詢
*/
@Test
public void testSelectColumnMap()
{
//以List集合形式返回查詢屬性 SELECT new map(g.gid, g.gname)
//String hql = "SELECT new map(g.gid AS id, g.gname AS name) FROM Grade AS g";
String hql = "SELECT new map(g.gid , g.gname ) FROM Grade AS g";
Query query = session.createQuery(hql);
List<Map> maps = query.list();
for (Map map : maps) {
//未定義屬性別名的獲取方式
System.out.println("id = " + map.get("0") + "name = " + map.get("1"));
//定義屬性別名的獲取方式
System.out.println("id = " + map.get("id") + "name = " + map.get("name"));
}
}
- 以自定義類型返回選擇的屬性
(1)先在Grade實(shí)體類添加構(gòu)造方法
public Grade(String gname, String gdesc) {
this.gname = gname;
this.gdesc = gdesc;
}
(2)測(cè)試程序
/**
* 以自定義方式返回查詢屬性，需要在查詢的實(shí)體類中定義構(gòu)造方法
* select語(yǔ)句中指定new 實(shí)體類名
*/
@Test
public void testSelectColumnCustomer()
{
String hql = "SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g";
Query query = session.createQuery(hql);
List<Grade> grades = query.list();
for (Grade grade : grades) {
//定義屬性別名的獲取方式
System.out.println("name = " + grade.getGname()+ "desc = " + grade.getGdesc());
}
}
四．where查詢
- 比較運(yùn)算符 =, <>, <, >, >=, <=
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid > 5
- null值判斷, is [not] null
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid is null
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid is not null
或
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid = null
- 范圍運(yùn)算：
- [not] in (列表)
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid > 5 AND g.gid in (8,10)
- [not] between value1 and value2, 屬性在value1和value2之間
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid > 5 AND g.gid in (8,10) AND g.gid BETWEEN 1 and 10
或
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.gid > 5 AND g.gid in (8,10) AND g.gid NOT BETWEEN 1 and 10
- 字符串模式匹配
- like
- 通配符百分號(hào)
%: 匹配任意個(gè)字符
模糊查詢包含北京的數(shù)據(jù)
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.name like '%北京%'
通配符下劃線 `_` ：匹配一個(gè)字符
查詢名字為以張開(kāi)頭，兩個(gè)字的數(shù)據(jù)
```
SELECT new Grade( g.gname , g.gdesc) FROM Grade AS g WHERE g.name like '張_'
```
* 邏輯運(yùn)算符,使用方式與sql語(yǔ)句一致
+ and(邏輯與)， or(邏輯或)
+ not (非)
* 集合運(yùn)算符
> 注意：會(huì)產(chǎn)生子查詢，個(gè)人不建議使用
+ is[not] empty 集合[不]為空，不包含任何元素
//查詢班級(jí)屬性中學(xué)生屬性不為空的班級(jí)信息
String hql = "SELECT new map(g.gid as id , g.gname as name ) FROM Grade AS g WHERE g.student2 is not empty";
解析為sql
select
grade0_.gid as col_0_0_,
grade0_.gname as col_1_0_
from
grade grade0_
where
exists (
select
student2x1_.sid
from
student2 student2x1_
where
grade0_.gid=student2x1_.gid
)
+ member of 元素屬于集合
String hql = "SELECT s FROM Student2 AS s WHERE s member of grade.student2";
解析為sql
select
student2x0_.sid as col_0_0_
from
student2 student2x0_ cross
join
grade grade1_
where
student2x0_.gid=grade1_.gid
and (
student2x0_.sid in (
select
student2x2_.sid
from
student2 student2x2_
where
grade1_.gid=student2x2_.gid
)
)
* 四則運(yùn)算
+ HQL語(yǔ)句中也可以使用 + - * / 四則運(yùn)算
String hql = "SELECT g FROM Grade AS g where g.score*2 > 800";
+ 四則運(yùn)算可以在where子句和select子句中使用
* 查詢單個(gè)對(duì)象
+ Query 接口的uniqueResult方法
/**
* 使用query.uniqueResult()返回一個(gè)對(duì)象（只返回一條記錄）
* 如果結(jié)果有多條則會(huì)報(bào)錯(cuò)
*/
@Test
public void testGetOne()
{
String hql = "SELECT g FROM Grade AS g where g.gid = 1 order by id asc";
Query query = session.createQuery(hql);
Grade grade = (Grade)query.uniqueResult();
System.out.println("name = " + grade.getGname());
}
* order by 子句
先按著s.gid正序排列，如果發(fā)現(xiàn)s.gid有相同的情況，那么以s.sid對(duì)s.gid相同的部分做倒序排列
SELECT s FROM Student AS s where order by s.gid asc, s.sid desc;
