欢迎来到Hibernate命名查询示例教程。我们看到了如何在Hibernate中使用HQL和本机SQL查询。如果有大量查询，它们将导致代码混乱，因为所有查询将散布在整个项目中。这就是为什么Hibernate提供命名查询的原因，我们可以在一个中央位置定义它们，并在代码的任何地方使用它们。我们可以为HQL和本机SQL都创建命名查询。
Hibernate命名查询
在 Hibernate 映射文件中或通过使用 JPA 注解 @NamedQuery 和 @NamedNativeQuery 来定义 Hibernate 命名查询。今天我们将研究它们的用法以及如何在简单的应用程序中使用 Hibernate 命名查询。我们将使用与 HQL 示例 中相同的数据库表，因此您可以查看该帖子以获取数据库设置 SQL 脚本。对于我们的 Hibernate 命名查询示例项目，我们将使用注解进行 Hibernate 映射。但是我们将在映射文件和实体 bean 类中创建一些命名查询。我们的最终项目结构如下图所示，我们将主要关注与 Hibernate 命名查询相关的组件。 
Hibernate 配置 XML
hibernate.cfg.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration SYSTEM "https://hibernate.sourceforge.net/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" />
<mapping resource="named-queries.hbm.xml" />
</session-factory>
</hibernate-configuration>
Hibernate 命名查询 XML
我们有一个 Hibernate 映射文件，其中只包含了 HQL 命名查询和 Native SQL 命名查询。named-queries.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"https://hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<query name="HQL_GET_ALL_EMPLOYEE">from Employee</query>
<query name="HQL_GET_EMPLOYEE_BY_ID">
<![CDATA[from Employee where emp_id = :id]]>
</query>
<query name="HQL_GET_EMPLOYEE_BY_SALARY">
<![CDATA[from Employee where emp_salary > :salary]]>
</query>
<sql-query name="SQL_GET_ALL_EMPLOYEE">
<![CDATA[select emp_id, emp_name, emp_salary from Employee]]>
</sql-query>
<sql-query name="SQL_GET_ALL_EMP_ADDRESS">
<![CDATA[select {e.*}, {a.*} from Employee e join Address a ON e.emp_id=a.emp_id]]>
<return alias="e" class="com.journaldev.hibernate.model.Employee" />
<return-join alias="a" property="e.address"></return-join>
</sql-query>
</hibernate-mapping>
query 元素用于 HQL 命名查询，sql-query 元素用于本地 SQL 命名查询。我们可以使用 return 元素声明结果集将映射到的实体。当我们有多个表的连接时，我们应该使用 return-join。我们应该使用 CDATA 来声明我们的 Hibernate 命名查询，以确保它被视为数据，否则 < 和 > 符号会破坏我们的映射 XML 文件。
Hibernate 命名查询 @NamedQuery 注解
我们有两个模型类 – Employee 和 Address。我们在 Address 类中定义了如下命名查询。
package com.journaldev.hibernate.model;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.NamedNativeQueries;
import javax.persistence.NamedNativeQuery;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
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")
@NamedQueries({ @NamedQuery(name = "@HQL_GET_ALL_ADDRESS",
query = "from Address") })
@NamedNativeQueries({ @NamedNativeQuery(name = "@SQL_GET_ALL_ADDRESS",
query = "select emp_id, address_line1, city, zipcode from 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
@PrimaryKeyJoinColumn
private 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;
}
@Override
public String toString() {
return "AddressLine1= " + addressLine1 + ", City=" + city
+ ", Zipcode=" + zipcode;
}
}
Hibernate 命名查询测试程序
让我们编写一个测试程序来使用上面定义的所有Hibernate命名查询。
package com.journaldev.hibernate.main;
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.Address;
import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;
public class HibernateNamedQueryExample {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
// 准备工作
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.getCurrentSession();
Transaction tx = session.beginTransaction();
//HQL命名查询示例
Query query = session.getNamedQuery("HQL_GET_ALL_EMPLOYEE");
List empList = query.list();
for (Employee emp : empList) {
System.out.println("List of Employees::" + emp.getId() + ","
+ emp.getAddress().getCity());
}
query = session.getNamedQuery("HQL_GET_EMPLOYEE_BY_ID");
query.setInteger("id", 2);
Employee emp = (Employee) query.uniqueResult();
System.out.println("Employee Name=" + emp.getName() + ", City="
+ emp.getAddress().getCity());
query = session.getNamedQuery("HQL_GET_EMPLOYEE_BY_SALARY");
query.setInteger("salary", 200);
empList = query.list();
for (Employee emp1 : empList) {
System.out.println("List of Employees::" + emp1.getId() + ","
+ emp1.getSalary());
}
query = session.getNamedQuery("@HQL_GET_ALL_ADDRESS");
List addressList = query.list();
for (Address addr : addressList) {
System.out.println("List of Address::" + addr.getId() + "::"
+ addr.getZipcode() + "::" + addr.getEmployee().getName());
}
//本机SQL命名查询示例
query = session.getNamedQuery("@SQL_GET_ALL_ADDRESS");
List addressObjArray = query.list();
for(Object[] row : addressObjArray){
for(Object obj : row){
System.out.print(obj + "::");
}
System.out.println("\n");
}
query = session.getNamedQuery("SQL_GET_ALL_EMP_ADDRESS");
addressObjArray = query.list();
for(Object[] row : addressObjArray){
Employee e = (Employee) row[0];
System.out.println("Employee Info::"+e);
Address a = (Address) row[1];
System.out.println("Address Info::"+a);
}
// 回滚以保存测试数据
tx.commit();
// 关闭Hibernate资源
sessionFactory.close();
}
}
当我们使用我们拥有的测试数据执行上述程序时，它会产生以下输出。
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 emp_id=?
Employee Name=David, City=Santa Clara
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 emp_salary>?
List of Employees::3,300.0
List of Employees::4,400.0
Hibernate: select address0_.emp_id as emp_id1_0_, address0_.address_line1 as address_2_0_, address0_.city as city3_0_, address0_.zipcode as zipcode4_0_ from ADDRESS address0_
List of Address::1::95129::Pankaj
List of Address::2::95051::David
List of Address::3::560100::Lisa
List of Address::4::100100::Jack
Hibernate: select emp_id, address_line1, city, zipcode from Address
1::Albany Dr::San Jose::95129::
2::Arques Ave::Santa Clara::95051::
3::BTM 1st Stage::Bangalore::560100::
4::City Centre::New Delhi::100100::
Hibernate: select e.emp_id as emp_id1_1_0_, e.emp_name as emp_name2_1_0_, e.emp_salary as emp_sala3_1_0_, a.emp_id as emp_id1_0_1_, a.address_line1 as address_2_0_1_, a.city as city3_0_1_, a.zipcode as zipcode4_0_1_ from Employee e join Address a ON e.emp_id=a.emp_id
Employee Info::Id= 1, Name= Pankaj, Salary= 100.0, {Address= AddressLine1= Albany Dr, City=San Jose, Zipcode=95129}
Address Info::AddressLine1= Albany Dr, City=San Jose, Zipcode=95129
Employee Info::Id= 2, Name= David, Salary= 200.0, {Address= AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051}
Address Info::AddressLine1= Arques Ave, City=Santa Clara, Zipcode=95051
Employee Info::Id= 3, Name= Lisa, Salary= 300.0, {Address= AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100}
Address Info::AddressLine1= BTM 1st Stage, City=Bangalore, Zipcode=560100
Employee Info::Id= 4, Name= Jack, Salary= 400.0, {Address= AddressLine1= City Centre, City=New Delhi, Zipcode=100100}
Address Info::AddressLine1= City Centre, City=New Delhi, Zipcode=100100
Hibernate命名查询重要点
关于Hibernate命名查询的一些重要点是；
- Hibernate命名查询帮助我们将查询分组到一个中心位置，而不是让它们散布在代码中的各个地方。
- 当创建Hibernate会话工厂时，Hibernate命名查询语法会受到检查，从而使应用程序在命名查询中出现任何错误时能够快速失败。
- Hibernate命名查询是全局的，意味着一旦定义，它就可以在整个应用程序中使用。
- 命名查询的一个主要缺点是很难调试，因为我们需要找出它的定义位置。
这就是Hibernate命名查询示例的全部内容，您可以从下面的链接下载示例项目。
Source:
https://www.digitalocean.com/community/tutorials/hibernate-named-query-example-namedquery