HQL or Hibernate Query Language is the object-oriented query language of Hibernate Framework. HQL is very similar to SQL except that we use Objects instead of table names, that makes it more close to object oriented programming.

HQL或Hibernate查询语言是Hibernate Framework的面向对象查询语言。 HQL与SQL非常相似，除了我们使用对象而不是表名，这使得它更接近面向对象的编程。

Hibernate查询语言– HQL (Hibernate Query Language – HQL)

HQL and Case Sensitivity: HQL is case-insensitive except for java class and variable names. So SeLeCT is the same as sELEct is the same as SELECT, but com.journaldev.model.Employee is not same as com.journaldev.model.EMPLOYEE.

HQL和区分大小写：除Java类和变量名称外，HQL不区分大小写。 因此， SeLeCT与sELEct相同，与SELECT相同，但是com.journaldev.model.Employee与com.journaldev.model.EMPLOYEE 。

Some of the commonly supported clauses in HQL are:

HQL中一些普遍支持的子句是：

1. HQL From: HQL From is same as select clause in SQL, from Employee is same as select * from Employee. We can also create alias such as from Employee emp or from Employee as emp.HQL From ：HQL From与SQL中的select子句相同， from Employee与select * from Employee相同。 我们还可以创建别名，例如from Employee emp或from Employee as emp 。
2. HQL Join : HQL supports inner join, left outer join, right outer join and full join. For example, select e.name, a.city from Employee e INNER JOIN e.address a. In this query, Employee class should have a variable named address. We will look into it in the example code.HQL联接 ：HQL支持内部联接 ，左外部联接 ，右外部联接和完全联接 。 例如， select e.name, a.city from Employee e INNER JOIN e.address a 。 在此查询中，Employee类应具有一个名为address的变量。 我们将在示例代码中对其进行研究。
3. Aggregate Functions: HQL supports commonly used aggregate functions such as count(*), count(distinct x), min(), max(), avg() and sum().聚合函数 ：HQL支持常用的聚合函数，例如count（*），count（distinct x），min（），max（），avg（）和sum（）。
4. Expressions: HQL supports arithmetic expressions (+, -, *, /), binary comparison operators (=, >=, <=, <>, !=, like), logical operations (and, or, not) etc.表达式 ：HQL支持算术表达式（+，-，*，/），二进制比较运算符（=，> =，<=，<>，！=等），逻辑运算（和，或，或不）。
5. HQL also supports ordre by and group by clauses.HQL还支持ordre by和group by子句。
6. HQL also supports sub-queries just like SQL queries.HQL还支持子查询，就像SQL查询一样。
7. HQL supports DDL, DML and executing store procedures too.HQL也支持DDL，DML和执行存储过程。

Let’s look at a simple example of using HQL in our program.

让我们看一个在程序中使用HQL的简单示例。

HQL示例数据库设置 (HQL Example Database Setup)

I am using MySQL database for my example, below script will create two tables Employee and Address. They have one-to-one mapping and I am inserting some demo data for my example.

我使用MySQL数据库作为示例，下面的脚本将创建两个表Employee和Address。 它们具有一对一的映射，我将为示例插入一些演示数据。

CREATE TABLE `Employee` (`emp_id` int(11) unsigned NOT NULL AUTO_INCREMENT,`emp_name` varchar(20) NOT NULL,`emp_salary` double(10,0) NOT NULL DEFAULT '0',PRIMARY KEY (`emp_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;CREATE TABLE `Address` (`emp_id` int(11) unsigned NOT NULL,`address_line1` varchar(50) NOT NULL DEFAULT '',`zipcode` varchar(10) DEFAULT NULL,`city` varchar(20) DEFAULT NULL,PRIMARY KEY (`emp_id`),CONSTRAINT `emp_fk_1` FOREIGN KEY (`emp_id`) REFERENCES `Employee` (`emp_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;INSERT INTO `Employee` (`emp_id`, `emp_name`, `emp_salary`)
VALUES(1, 'Pankaj', 100),(2, 'David', 200),(3, 'Lisa', 300),(4, 'Jack', 400);INSERT INTO `Address` (`emp_id`, `address_line1`, `zipcode`, `city`)
VALUES(1, 'Albany Dr', '95129', 'San Jose'),(2, 'Arques Ave', '95051', 'Santa Clara'),(3, 'BTM 1st Stage', '560100', 'Bangalore'),(4, 'City Centre', '100100', 'New Delhi');commit;

Create a maven project in Eclipse or the IDE you are using, our final project will look like below image.

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。

HibernateMaven依赖关系 (Hibernate Maven Dependencies)

Our final pom.xml contains dependencies for Hibernate and MySQL driver.

我们最终的pom.xml包含Hibernate和MySQL驱动程序的依赖项。

<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"><modelVersion>4.0.0</modelVersion><groupId>com.journaldev.hibernate</groupId><artifactId>HQLExample</artifactId><version>0.0.1-SNAPSHOT</version><dependencies><dependency><groupId>org.hibernate</groupId><artifactId>hibernate-core</artifactId><version>4.3.5.Final</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.0.5</version></dependency></dependencies>
</project>

Hibernate配置XML (Hibernate Configuration XML)

Our hibernate configuration xml file contains database connection related properties and mapping classes. I will be using annotations for Hibernate mapping.

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。 我将使用注释进行Hibernate映射。

hibernate.cfg.xml code:

hibernate.cfg.xml代码：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC"-//Hibernate/Hibernate Configuration DTD 3.0//EN""https://hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration><session-factory><property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property><property name="hibernate.connection.password">pankaj123</property><property name="hibernate.connection.url">jdbc:mysql://localhost/TestDB</property><property name="hibernate.connection.username">pankaj</property><property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property><property name="hibernate.current_session_context_class">thread</property><property name="hibernate.show_sql">true</property><mapping class="com.journaldev.hibernate.model.Employee"/><mapping class="com.journaldev.hibernate.model.Address"/></session-factory>
</hibernate-configuration>

Hibernate SessionFactory Utility类 (Hibernate SessionFactory Utility class)

We have a utility class to configure hibernate SessionFactory.

我们有一个实用程序类来配置HibernateSessionFactory。

package com.journaldev.hibernate.util;import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;public class HibernateUtil {private static SessionFactory sessionFactory;private static SessionFactory buildSessionFactory() {try {// Create the SessionFactory from hibernate.cfg.xmlConfiguration configuration = new Configuration();configuration.configure("hibernate.cfg.xml");System.out.println("Hibernate Configuration loaded");ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();System.out.println("Hibernate serviceRegistry created");SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);return sessionFactory;}catch (Throwable ex) {System.err.println("Initial SessionFactory creation failed." + ex);ex.printStackTrace();throw new ExceptionInInitializerError(ex);}}public static SessionFactory getSessionFactory() {if(sessionFactory == null) sessionFactory = buildSessionFactory();return sessionFactory;}
}

具有基于注释的映射的模型类 (Model Classes with Annotation based mapping)

Our model classes with JPA annotations looks like below.

我们的带有JPA批注的模型类如下所示。

package com.journaldev.hibernate.model;import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;import org.hibernate.annotations.Cascade;@Entity
@Table(name = "EMPLOYEE")
public class Employee {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)@Column(name = "emp_id")private long id;@Column(name = "emp_name")private String name;@Column(name = "emp_salary")private double salary;@OneToOne(mappedBy = "employee")@Cascade(value = org.hibernate.annotations.CascadeType.ALL)private Address address;public long getId() {return id;}public void setId(long id) {this.id = id;}public Address getAddress() {return address;}public void setAddress(Address address) {this.address = address;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getSalary() {return salary;}public void setSalary(double salary) {this.salary = salary;}}

package com.journaldev.hibernate.model;import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;
import javax.persistence.Table;import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;@Entity
@Table(name = "ADDRESS")
public class Address {@Id@Column(name = "emp_id", unique = true, nullable = false)@GeneratedValue(generator = "gen")@GenericGenerator(name = "gen", strategy = "foreign", parameters = { @Parameter(name = "property", value = "employee") })private long id;@Column(name = "address_line1")private String addressLine1;@Column(name = "zipcode")private String zipcode;@Column(name = "city")private String city;@OneToOne@PrimaryKeyJoinColumnprivate Employee employee;public long getId() {return id;}public void setId(long id) {this.id = id;}public String getAddressLine1() {return addressLine1;}public void setAddressLine1(String addressLine1) {this.addressLine1 = addressLine1;}public String getZipcode() {return zipcode;}public void setZipcode(String zipcode) {this.zipcode = zipcode;}public String getCity() {return city;}public void setCity(String city) {this.city = city;}public Employee getEmployee() {return employee;}public void setEmployee(Employee employee) {this.employee = employee;}}

HQL示例测试类 (HQL Example Test Class)

Let’s see how to use HQL in java programs.

让我们看看如何在Java程序中使用HQL。

package com.journaldev.hibernate.main;import java.util.Arrays;
import java.util.List;import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;public class HQLExamples {@SuppressWarnings("unchecked")public static void main(String[] args) {//Prep workSessionFactory sessionFactory = HibernateUtil.getSessionFactory();Session session = sessionFactory.getCurrentSession();//HQL example - Get All EmployeesTransaction tx = session.beginTransaction();Query query = session.createQuery("from Employee");List<Employee> empList = query.list();for(Employee emp : empList){System.out.println("List of Employees::"+emp.getId()+","+emp.getAddress().getCity());}//HQL example - Get Employee with idquery = session.createQuery("from Employee where id= :id");query.setLong("id", 3);Employee emp = (Employee) query.uniqueResult();System.out.println("Employee Name="+emp.getName()+", City="+emp.getAddress().getCity());//HQL pagination examplequery = session.createQuery("from Employee");query.setFirstResult(0); //starts with 0query.setFetchSize(2);empList = query.list();for(Employee emp4 : empList){System.out.println("Paginated Employees::"+emp4.getId()+","+emp4.getAddress().getCity());}//HQL Update Employeequery = session.createQuery("update Employee set name= :name where id= :id");query.setParameter("name", "Pankaj Kumar");query.setLong("id", 1);int result = query.executeUpdate();System.out.println("Employee Update Status="+result);//HQL Delete Employee, we need to take care of foreign key constraints tooquery = session.createQuery("delete from Address where id= :id");query.setLong("id", 4);result = query.executeUpdate();System.out.println("Address Delete Status="+result);query = session.createQuery("delete from Employee where id= :id");query.setLong("id", 4);result = query.executeUpdate();System.out.println("Employee Delete Status="+result);//HQL Aggregate function examplesquery = session.createQuery("select sum(salary) from Employee");double sumSalary = (Double) query.uniqueResult();System.out.println("Sum of all Salaries= "+sumSalary);//HQL join examplesquery = session.createQuery("select e.name, a.city from Employee e "+ "INNER JOIN e.address a");List<Object[]> list = query.list();for(Object[] arr : list){System.out.println(Arrays.toString(arr));}//HQL group by and like examplequery = session.createQuery("select e.name, sum(e.salary), count(e)"+ " from Employee e where e.name like '%i%' group by e.name");List<Object[]> groupList = query.list();for(Object[] arr : groupList){System.out.println(Arrays.toString(arr));}//HQL order by examplequery = session.createQuery("from Employee e order by e.id desc");empList = query.list();for(Employee emp3 : empList){System.out.println("ID Desc Order Employee::"+emp3.getId()+","+emp3.getAddress().getCity());}//rolling back to save the test datatx.rollback();//closing hibernate resourcessessionFactory.close();}}

Notice that I am using HQL for Select, Update and Delete operations. It also shows how to use HQL Join and HQL Aggregate functions.

请注意，我正在使用HQL进行选择，更新和删除操作。 它还显示了如何使用HQL Join和HQL Aggregate函数。

When I run above hql example program, we get following output.

当我在hql示例程序之上运行时，我们得到以下输出。

May 22, 2014 1:55:37 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {4.0.4.Final}
May 22, 2014 1:55:37 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {4.3.5.Final}
May 22, 2014 1:55:37 PM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
May 22, 2014 1:55:37 PM org.hibernate.cfg.Environment buildBytecodeProvider
INFO: HHH000021: Bytecode provider name : javassist
May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration configure
INFO: HHH000043: Configuring from resource: hibernate.cfg.xml
May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration getConfigurationInputStream
INFO: HHH000040: Configuration resource: hibernate.cfg.xml
May 22, 2014 1:55:37 PM org.hibernate.cfg.Configuration doConfigure
INFO: HHH000041: Configured SessionFactory: null
Hibernate Configuration loaded
Hibernate serviceRegistry created
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH000402: Using Hibernate built-in connection pool (not for production use!)
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH000401: using driver [com.mysql.jdbc.Driver] at URL [jdbc:mysql://localhost/TestDB]
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH000046: Connection properties: {user=pankaj, password=****}
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH000006: Autocommit mode: false
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
May 22, 2014 1:55:37 PM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQLDialect
May 22, 2014 1:55:37 PM org.hibernate.engine.jdbc.internal.LobCreatorBuilder useContextualLobCreation
INFO: HHH000423: Disabling contextual LOB creation as JDBC driver reported JDBC version [3] less than 4
May 22, 2014 1:55:38 PM org.hibernate.engine.transaction.internal.TransactionFactoryInitiator initiateService
INFO: HHH000399: Using default transaction strategy (direct JDBC transactions)
May 22, 2014 1:55:38 PM org.hibernate.hql.internal.ast.ASTQueryTranslatorFactory <init>
INFO: HHH000397: Using ASTQueryTranslatorFactory
Hibernate: 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_
Hibernate: 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=?
Hibernate: 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=?
Hibernate: 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=?
Hibernate: 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=?
List of Employees::1,San Jose
List of Employees::2,Santa Clara
List of Employees::3,Bangalore
List of Employees::4,New Delhi
Hibernate: 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=?
Employee Name=Lisa, City=Bangalore
Hibernate: 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_
Paginated Employees::1,San Jose
Paginated Employees::2,Santa Clara
Paginated Employees::3,Bangalore
Paginated Employees::4,New Delhi
Hibernate: update EMPLOYEE set emp_name=? where emp_id=?
Employee Update Status=1
Hibernate: delete from ADDRESS where emp_id=?
Address Delete Status=1
Hibernate: delete from EMPLOYEE where emp_id=?
Employee Delete Status=1
Hibernate: select sum(employee0_.emp_salary) as col_0_0_ from EMPLOYEE employee0_
Sum of all Salaries= 600.0
Hibernate: 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
[Pankaj Kumar, San Jose]
[David, Santa Clara]
[Lisa, Bangalore]
Hibernate: 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
[David, 200.0, 1]
[Lisa, 300.0, 1]
Hibernate: 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
ID Desc Order Employee::3,Bangalore
ID Desc Order Employee::2,Santa Clara
ID Desc Order Employee::1,San Jose
May 22, 2014 1:55:38 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH000030: Cleaning up connection pool [jdbc:mysql://localhost/TestDB]

Notice that once delete operation is performed, further operations are not showing that record data (sum of salary is 600). However I am rolling back the transaction, so the data in table will remain unchanged. Change the code to commit the transaction and it will be reflected in the database tables.

请注意，一旦执行了删除操作，其他操作就不会显示该记录数据（薪金总和为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。

I don’t like using HQL query a lot because as you can see that we need to take care of table mappings in our code. If we will use Session to delete the Employee object, it will delete the record from both the tables.

我不太喜欢使用HQL查询，因为您可以看到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。

You can download the sample hql example project from below link and try more examples.

您可以从下面的链接下载示例hql示例项目，然后尝试更多示例。

翻译自: https://www.journaldev.com/2954/hibernate-query-language-hql-example-tutorial