HQL或Hibernate Query Language是Hibernate框架的面向对象查询语言。HQL与SQL非常相似，不同之处在于我们使用对象而不是表名，这使它更接近面向对象编程。
Hibernate查询语言- HQL
HQL和大小写敏感性 ：HQL不区分大小写，Java类和变量名除外。所以SeLeCT和sELEct和SELECT一样，但是com.journaldev.model.Employee和com.journaldev.model.EMPLOYEE不一样。HQL中一些通常支持的条款是：
1.HQL from ：HQL from与SQL中的SELECT子句相同，From Employee与Select* from Employee相同。我们也可以创建别名，如From Employee Emp或From Employee as Emp。
2.HQL Join ：HQL支持内部Join、Left Out Join、Right Out Join和Full Join。例如，Select e.name，a.City from Employee e Enter Join e.Address a。在这个查询中，Employee类应该有一个名为Address的变量。我们将在示例代码中对其进行研究。
3.聚合函数 ：HQL支持COUNT(* )、COUNT(DISTINCT X)、MIN()、max()、avg()、sum()等常用聚合函数。
4.表达式 ：HQL支持算术表达式(+、-、* 、/)、二元比较运算符(=、>=、<=、<>、！=、LIKE)、逻辑运算(AND、OR、NOT)等。
5.HQL还支持ORDRE BY和GROUP BY子句。
6.HQL也支持像SQL查询一样的子查询。
7.HQL也支持DDL、DML和执行存储过程。
让我们看一个在我们的程序中使用HQL的简单示例。
HQL数据库设置示例
我正在使用MySQL数据库作为我的示例，下面的脚本将创建两个表Employee和Address。它们有一对一的映射，我正在为我的示例插入一些演示数据。
1CREATE TABLE `Employee` (
2 `emp_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
3 `emp_name` varchar(20) NOT NULL,
4 `emp_salary` double(10,0) NOT NULL DEFAULT '0',
5 PRIMARY KEY (`emp_id`)
6) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
7
8CREATE TABLE `Address` (
9 `emp_id` int(11) unsigned NOT NULL,
10 `address_line1` varchar(50) NOT NULL DEFAULT '',
11 `zipcode` varchar(10) DEFAULT NULL,
12 `city` varchar(20) DEFAULT NULL,
13 PRIMARY KEY (`emp_id`),
14 CONSTRAINT `emp_fk_1` FOREIGN KEY (`emp_id`) REFERENCES `Employee` (`emp_id`)
15) ENGINE=InnoDB DEFAULT CHARSET=utf8;
16
17INSERT INTO `Employee` (`emp_id`, `emp_name`, `emp_salary`)
18VALUES
19 (1, 'Pankaj', 100),
20 (2, 'David', 200),
21 (3, 'Lisa', 300),
22 (4, 'Jack', 400);
23
24INSERT INTO `Address` (`emp_id`, `address_line1`, `zipcode`, `city`)
25VALUES
26 (1, 'Albany Dr', '95129', 'San Jose'),
27 (2, 'Arques Ave', '95051', 'Santa Clara'),
28 (3, 'BTM 1st Stage', '560100', 'Bangalore'),
29 (4, 'City Centre', '100100', 'New Delhi');
30
31commit;
在您正在使用的Eclipse或IDE中创建一个Maven项目，我们的最终项目将如下图所示。
Hibernate Maven配置
我们最终的pom.xml包含Hibernate和MySQL驱动程序的依赖项。
1<project xmlns="https://maven.apache.org/POM/4.0.0" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
2 <modelVersion>4.0.0</modelVersion>
3 <groupId>com.journaldev.hibernate</groupId>
4 <artifactId>HQLExample</artifactId>
5 <version>0.0.1-SNAPSHOT</version>
6 <dependencies>
7 <dependency>
8 <groupId>org.hibernate</groupId>
9 <artifactId>hibernate-core</artifactId>
10 <version>4.3.5.Final</version>
11 </dependency>
12 <dependency>
13 <groupId>mysql</groupId>
14 <artifactId>mysql-connector-java</artifactId>
15 <version>5.0.5</version>
16 </dependency>
17 </dependencies>
18</project>
Hibernate配置XML
我们的Hibernate配置XML文件包含与数据库连接相关的属性和映射类。我将使用注解进行Hibernate映射。Hibernate.cfg.xml代码：
1<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE hibernate-configuration PUBLIC
3 "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
4 "https://hibernate.org/dtd/hibernate-configuration-3.0.dtd">
5<hibernate-configuration>
6 <session-factory>
7 <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
8 <property name="hibernate.connection.password">pankaj123</property>
9 <property name="hibernate.connection.url">jdbc:mysql://localhost/TestDB</property>
10 <property name="hibernate.connection.username">pankaj</property>
11 <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
12
13 <property name="hibernate.current_session_context_class">thread</property>
14 <property name="hibernate.show_sql">true</property>
15
16 <mapping class="com.journaldev.hibernate.model.Employee"/>
17 <mapping class="com.journaldev.hibernate.model.Address"/>
18 </session-factory>
19</hibernate-configuration>
Hibernate SessionFactory实用程序类
我们有一个实用程序类来配置Hibernate SessionFactory。
1package com.journaldev.hibernate.util;
2
3import org.hibernate.SessionFactory;
4import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
5import org.hibernate.cfg.Configuration;
6import org.hibernate.service.ServiceRegistry;
7
8public class HibernateUtil {
9
10 private static SessionFactory sessionFactory;
11
12 private static SessionFactory buildSessionFactory() {
13 try {
14 // Create the SessionFactory from hibernate.cfg.xml
15 Configuration configuration = new Configuration();
16 configuration.configure("hibernate.cfg.xml");
17 System.out.println("Hibernate Configuration loaded");
18
19 ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
20 System.out.println("Hibernate serviceRegistry created");
21
22 SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
23
24 return sessionFactory;
25 }
26 catch (Throwable ex) {
27 System.err.println("Initial SessionFactory creation failed." + ex);
28 ex.printStackTrace();
29 throw new ExceptionInInitializerError(ex);
30 }
31 }
32
33 public static SessionFactory getSessionFactory() {
34 if(sessionFactory == null) sessionFactory = buildSessionFactory();
35 return sessionFactory;
36 }
37}
基于注释映射的模型类
我们带有JPA注释的模型类如下所示。
1package com.journaldev.hibernate.model;
2
3import javax.persistence.Column;
4import javax.persistence.Entity;
5import javax.persistence.GeneratedValue;
6import javax.persistence.GenerationType;
7import javax.persistence.Id;
8import javax.persistence.OneToOne;
9import javax.persistence.Table;
10
11import org.hibernate.annotations.Cascade;
12
13@Entity
14@Table(name = "EMPLOYEE")
15public class Employee {
16
17 @Id
18 @GeneratedValue(strategy = GenerationType.IDENTITY)
19 @Column(name = "emp_id")
20 private long id;
21
22 @Column(name = "emp_name")
23 private String name;
24
25 @Column(name = "emp_salary")
26 private double salary;
27
28 @OneToOne(mappedBy = "employee")
29 @Cascade(value = org.hibernate.annotations.CascadeType.ALL)
30 private Address address;
31
32 public long getId() {
33 return id;
34 }
35
36 public void setId(long id) {
37 this.id = id;
38 }
39
40 public Address getAddress() {
41 return address;
42 }
43
44 public void setAddress(Address address) {
45 this.address = address;
46 }
47
48 public String getName() {
49 return name;
50 }
51
52 public void setName(String name) {
53 this.name = name;
54 }
55
56 public double getSalary() {
57 return salary;
58 }
59
60 public void setSalary(double salary) {
61 this.salary = salary;
62 }
63
64}
1package com.journaldev.hibernate.model;
2
3import javax.persistence.Column;
4import javax.persistence.Entity;
5import javax.persistence.GeneratedValue;
6import javax.persistence.Id;
7import javax.persistence.OneToOne;
8import javax.persistence.PrimaryKeyJoinColumn;
9import javax.persistence.Table;
10
11import org.hibernate.annotations.GenericGenerator;
12import org.hibernate.annotations.Parameter;
13
14@Entity
15@Table(name = "ADDRESS")
16public class Address {
17
18 @Id
19 @Column(name = "emp_id", unique = true, nullable = false)
20 @GeneratedValue(generator = "gen")
21 @GenericGenerator(name = "gen", strategy = "foreign",
22 parameters = { @Parameter(name = "property", value = "employee") })
23 private long id;
24
25 @Column(name = "address_line1")
26 private String addressLine1;
27
28 @Column(name = "zipcode")
29 private String zipcode;
30
31 @Column(name = "city")
32 private String city;
33
34 @OneToOne
35 @PrimaryKeyJoinColumn
36 private Employee employee;
37
38 public long getId() {
39 return id;
40 }
41
42 public void setId(long id) {
43 this.id = id;
44 }
45
46 public String getAddressLine1() {
47 return addressLine1;
48 }
49
50 public void setAddressLine1(String addressLine1) {
51 this.addressLine1 = addressLine1;
52 }
53
54 public String getZipcode() {
55 return zipcode;
56 }
57
58 public void setZipcode(String zipcode) {
59 this.zipcode = zipcode;
60 }
61
62 public String getCity() {
63 return city;
64 }
65
66 public void setCity(String city) {
67 this.city = city;
68 }
69
70 public Employee getEmployee() {
71 return employee;
72 }
73
74 public void setEmployee(Employee employee) {
75 this.employee = employee;
76 }
77
78}
HQL示例测试类
让我们看看如何在Java程序中使用HQL。
1package com.journaldev.hibernate.main;
2
3import java.util.Arrays;
4import java.util.List;
5
6import org.hibernate.Query;
7import org.hibernate.Session;
8import org.hibernate.SessionFactory;
9import org.hibernate.Transaction;
10
11import com.journaldev.hibernate.model.Employee;
12import com.journaldev.hibernate.util.HibernateUtil;
13
14public class HQLExamples {
15
16 @SuppressWarnings("unchecked")
17 public static void main(String[] args) {
18
19 //Prep work
20 SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
21 Session session = sessionFactory.getCurrentSession();
22
23 //HQL example - Get All Employees
24 Transaction tx = session.beginTransaction();
25 Query query = session.createQuery("from Employee");
26 List<Employee> empList = query.list();
27 for(Employee emp : empList){
28 System.out.println("List of Employees::"+emp.getId()+","+emp.getAddress().getCity());
29 }
30
31 //HQL example - Get Employee with id
32 query = session.createQuery("from Employee where id= :id");
33 query.setLong("id", 3);
34 Employee emp = (Employee) query.uniqueResult();
35 System.out.println("Employee Name="+emp.getName()+", City="+emp.getAddress().getCity());
36
37 //HQL pagination example
38 query = session.createQuery("from Employee");
39 query.setFirstResult(0); //starts with 0
40 query.setFetchSize(2);
41 empList = query.list();
42 for(Employee emp4 : empList){
43 System.out.println("Paginated Employees::"+emp4.getId()+","+emp4.getAddress().getCity());
44 }
45
46 //HQL Update Employee
47 query = session.createQuery("update Employee set name= :name where id= :id");
48 query.setParameter("name", "Pankaj Kumar");
49 query.setLong("id", 1);
50 int result = query.executeUpdate();
51 System.out.println("Employee Update Status="+result);
52
53 //HQL Delete Employee, we need to take care of foreign key constraints too
54 query = session.createQuery("delete from Address where id= :id");
55 query.setLong("id", 4);
56 result = query.executeUpdate();
57 System.out.println("Address Delete Status="+result);
58
59 query = session.createQuery("delete from Employee where id= :id");
60 query.setLong("id", 4);
61 result = query.executeUpdate();
62 System.out.println("Employee Delete Status="+result);
63
64 //HQL Aggregate function examples
65 query = session.createQuery("select sum(salary) from Employee");
66 double sumSalary = (Double) query.uniqueResult();
67 System.out.println("Sum of all Salaries= "+sumSalary);
68
69 //HQL join examples
70 query = session.createQuery("select e.name, a.city from Employee e "
71 + "INNER JOIN e.address a");
72 List<Object[]> list = query.list();
73 for(Object[] arr : list){
74 System.out.println(Arrays.toString(arr));
75 }
76
77 //HQL group by and like example
78 query = session.createQuery("select e.name, sum(e.salary), count(e)"
79 + " from Employee e where e.name like '%i%' group by e.name");
80 List<Object[]> groupList = query.list();
81 for(Object[] arr : groupList){
82 System.out.println(Arrays.toString(arr));
83 }
84
85 //HQL order by example
86 query = session.createQuery("from Employee e order by e.id desc");
87 empList = query.list();
88 for(Employee emp3 : empList){
89 System.out.println("ID Desc Order Employee::"+emp3.getId()+","+emp3.getAddress().getCity());
90 }
91
92 //rolling back to save the test data
93 tx.rollback();
94
95 //closing hibernate resources
96 sessionFactory.close();
97 }
98
99}
请注意，我正在使用HQL进行选择、更新和删除操作。它还展示了如何使用HQL Join和HQL聚合函数。当我运行上面的hql示例程序时，我们得到以下输出。
1May 22, 2014 1:55:37 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
2INFO: HCANN000001: Hibernate Commons Annotations {4.0.4.Final}
3May 22, 2014 1:55:37 PM org.hibernate.Version logVersion
4INFO: HHH000412: Hibernate Core {4.3.5.Final}
5May 22, 2014 1:55:37 PM org.hibernate.cfg.Environment <clinit>
6INFO: HHH000206: hibernate.properties not found
7May 22, 2014 1:55:37 PM org.hibernate.cfg.Environment buildBytecodeProvider
8INFO: HHH000021: Bytecode provider name : javassist
9May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration configure
10INFO: HHH000043: Configuring from resource: hibernate.cfg.xml
11May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration getConfigurationInputStream
12INFO: HHH000040: Configuration resource: hibernate.cfg.xml
13May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration doConfigure
14INFO: HHH000041: Configured SessionFactory: null
15Hibernate Configuration loaded
16Hibernate serviceRegistry created
17May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
18WARN: HHH000402: Using Hibernate built-in connection pool (not for production use!)
19May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
20INFO: HHH000401: using driver [com.mysql.jdbc.Driver] at URL [jdbc:mysql://localhost/TestDB]
21May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
22INFO: HHH000046: Connection properties: {user=pankaj, password=****}
23May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
24INFO: HHH000006: Autocommit mode: false
25May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
26INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
27May 22, 2014 1:55:37 PM org.hibernate.dialect.Dialect <init>
28INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQLDialect
29May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.internal.LobCreatorBuilder useContextualLobCreation
30INFO: HHH000423: Disabling contextual LOB creation as JDBC driver reported JDBC version [3] less than 4
31May 22, 2014 1:55:38 PM org.hibernate.engine.transaction.internal.TransactionFactoryInitiator initiateService
32INFO: HHH000399: Using default transaction strategy (direct JDBC transactions)
33May 22, 2014 1:55:38 PM org.hibernate.hql.internal.ast.ASTQueryTranslatorFactory <init>
34INFO: HHH000397: Using ASTQueryTranslatorFactory
35Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_
36Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
37Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
38Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
39Hibernate: select address0_.emp_id as emp_id1_0_0_, address0_.address_line1 as address_2_0_0_, address0_.city as city3_0_0_, address0_.zipcode as zipcode4_0_0_, employee1_.emp_id as emp_id1_1_1_, employee1_.emp_name as emp_name2_1_1_, employee1_.emp_salary as emp_sala3_1_1_ from ADDRESS address0_ left outer join EMPLOYEE employee1_ on address0_.emp_id=employee1_.emp_id where address0_.emp_id=?
40List of Employees::1,San Jose
41List of Employees::2,Santa Clara
42List of Employees::3,Bangalore
43List of Employees::4,New Delhi
44Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_ where employee0_.emp_id=?
45Employee Name=Lisa, City=Bangalore
46Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_
47Paginated Employees::1,San Jose
48Paginated Employees::2,Santa Clara
49Paginated Employees::3,Bangalore
50Paginated Employees::4,New Delhi
51Hibernate: update EMPLOYEE set emp_name=? where emp_id=?
52Employee Update Status=1
53Hibernate: delete from ADDRESS where emp_id=?
54Address Delete Status=1
55Hibernate: delete from EMPLOYEE where emp_id=?
56Employee Delete Status=1
57Hibernate: select sum(employee0_.emp_salary) as col_0_0_ from EMPLOYEE employee0_
58Sum of all Salaries= 600.0
59Hibernate: select employee0_.emp_name as col_0_0_, address1_.city as col_1_0_ from EMPLOYEE employee0_ inner join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id
60[Pankaj Kumar, San Jose]
61[David, Santa Clara]
62[Lisa, Bangalore]
63Hibernate: select employee0_.emp_name as col_0_0_, sum(employee0_.emp_salary) as col_1_0_, count(employee0_.emp_id) as col_2_0_ from EMPLOYEE employee0_ where employee0_.emp_name like '%i%' group by employee0_.emp_name
64[David, 200.0, 1]
65[Lisa, 300.0, 1]
66Hibernate: select employee0_.emp_id as emp_id1_1_, employee0_.emp_name as emp_name2_1_, employee0_.emp_salary as emp_sala3_1_ from EMPLOYEE employee0_ order by employee0_.emp_id desc
67ID Desc Order Employee::3,Bangalore
68ID Desc Order Employee::2,Santa Clara
69ID Desc Order Employee::1,San Jose
70May 22, 2014 1:55:38 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
71INFO: HHH000030: Cleaning up connection pool [jdbc:mysql://localhost/TestDB]
请注意，一旦执行了删除操作，进一步的操作将不会显示该记录数据(工资总和为600)。但是，我正在回滚事务，因此表中的数据将保持不变。更改代码以提交事务，它将反映在数据库表中。我不太喜欢使用HQL查询，因为如您所见，我们需要在代码中处理表映射。如果我们将使用Session删除Employee对象，它将从两个表中删除记录。您可以从下面的链接下载示例hql示例项目，并尝试更多示例。