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教程 > Hibernate 教程 > Hibernate 基础
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Hibernate 本机 SQL
如果想利用数据库特定的功能，例如查询提示或 Oracle 中的 CONNECT 关键字，我们可以使用本机 SQL 来表示数据库查询。 Hibernate 允许我们为所有创建、更新、删除和加载操作指定手写 SQL，包括存储过程。
我们的应用程序将使用会话接口上的 createSQLQuery() 方法从会话创建本机 SQL 查询
public SQLQuery createSQLQuery(String sqlString) throws HibernateException
将包含 SQL 查询的字符串传递给 createSQLQuery() 方法后，我们可以使用 addEntity()、addJoin() 和 addScalar() 方法将 SQL 结果与现有 Hibernate 实体、连接或标量结果相关联。
标量查询
最基本的 SQL 查询是从一个或多个表中获取标量（值）列表。 以下是将本机 SQL 用于标量值的语法
String sql = "SELECT first_name, salary FROM employee";
SQLQuery query = session.createSQLQuery(sql);
query.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP);
List results = query.list();
实体查询
上面的查询都是关于返回标量值，基本上是从结果集中返回“原始”值。 以下是通过 addEntity() 从本机 sql 查询中获取整体实体对象的语法。
String sql = "SELECT * FROM employee";
SQLQuery query = session.createSQLQuery(sql);
query.addEntity(Employee.class);
List results = query.list();
命名 SQL 查询
以下是通过 addEntity() 并使用命名 SQL 查询从本机 sql 查询中获取实体对象的语法。
String sql = "SELECT * FROM employee WHERE id = :employee_id";
SQLQuery query = session.createSQLQuery(sql);
query.addEntity(Employee.class);
query.setParameter("employee_id", 10);
List results = query.list();
本机 SQL 示例
考虑以下 POJO 类
public class Employee {
private int id;
private String firstName;
private String lastName;
private int salary;
public Employee() {}
public Employee(String fname, String lname, int salary) {
this.firstName = fname;
this.lastName = lname;
this.salary = salary;
}
public int getId() {
return id;
}
public void setId( int id ) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName( String first_name ) {
this.firstName = first_name;
}
public String getLastName() {
return lastName;
}
public void setLastName( String last_name ) {
this.lastName = last_name;
}
public int getSalary() {
return salary;
}
public void setSalary( int salary ) {
this.salary = salary;
}
}
让我们创建以下 employee 表来存储 Employee 对象
create table employee (
id INT NOT NULL auto_increment,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary INT default NULL,
PRIMARY KEY (id)
);
以下是映射文件
<?xml version = "1.0" encoding = "utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name = "Employee" table = "employee">
<meta attribute = "class-description">
This class contains the employee detail.
</meta>
<id name = "id" type = "int" column = "id">
<generator class="native"/>
</id>
<property name = "firstName" column = "first_name" type = "string"/>
<property name = "lastName" column = "last_name" type = "string"/>
<property name = "salary" column = "salary" type = "int"/>
</class>
</hibernate-mapping>
最后，我们将使用 main() 方法创建我们的应用程序类来运行我们将使用本机 SQL 查询的应用程序
import java.util.*;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.SQLQuery;
import org.hibernate.Criteria;
import org.hibernate.Hibernate;
import org.hibernate.cfg.Configuration;
public class ManageEmployee {
private static SessionFactory factory;
public static void main(String[] args) {
try {
factory = new Configuration().configure().buildSessionFactory();
} catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
ManageEmployee ME = new ManageEmployee();
/* 在数据库中添加一些员工记录 */
Integer empID1 = ME.addEmployee("Zara", "Ali", 2000);
Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
Integer empID3 = ME.addEmployee("John", "Paul", 5000);
Integer empID4 = ME.addEmployee("Mohd", "Yasee", 3000);
/* 使用标量查询列出员工及其工资 */
ME.listEmployeesScalar();
/* 使用实体查询列出完整的员工信息 */
ME.listEmployeesEntity();
}
/* 在数据库中创建员工的方法 */
public Integer addEmployee(String fname, String lname, int salary){
Session session = factory.openSession();
Transaction tx = null;
Integer employeeID = null;
try {
tx = session.beginTransaction();
Employee employee = new Employee(fname, lname, salary);
employeeID = (Integer) session.save(employee);
tx.commit();
} catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
return employeeID;
}
/* 使用标量查询读取所有员工的方法 */
public void listEmployeesScalar( ){
Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
String sql = "SELECT first_name, salary FROM employee";
SQLQuery query = session.createSQLQuery(sql);
query.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP);
List data = query.list();
for(Object object : data) {
Map row = (Map)object;
System.out.print("First Name: " + row.get("first_name"));
System.out.println(", Salary: " + row.get("salary"));
}
tx.commit();
} catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
}
/* 使用实体查询读取所有员工的方法 */
public void listEmployeesEntity( ){
Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
String sql = "SELECT * FROM employee";
SQLQuery query = session.createSQLQuery(sql);
query.addEntity(Employee.class);
List employees = query.list();
for (Iterator iterator = employees.iterator(); iterator.hasNext();){
Employee employee = (Employee) iterator.next();
System.out.print("First Name: " + employee.getFirstName());
System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
}
tx.commit();
} catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
}
}
编译和执行
以下是编译和运行上述应用程序的步骤。 在继续编译和执行之前，请确保已正确设置 PATH 和 CLASSPATH。
- 按照配置章节中的说明创建 hibernate.cfg.xml 配置文件。
- 如上所示创建Employee.hbm.xml 映射文件。
- 如上所示创建Employee.java 源文件并编译它。
- 如上所示创建 ManageEmployee.java 源文件并编译它。
- 执行 ManageEmployee 二进制文件来运行程序。
我们将获得以下结果，并且将在 employee 表中创建记录。
$ java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........
First Name: Zara, Salary: 2000
First Name: Daisy, Salary: 5000
First Name: John, Salary: 5000
First Name: Mohd, Salary: 3000
First Name: Zara Last Name: Ali Salary: 2000
First Name: Daisy Last Name: Das Salary: 5000
First Name: John Last Name: Paul Salary: 5000
First Name: Mohd Last Name: Yasee Salary: 3000
如果检查你的 employee 表，它应该有以下记录
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 26 | Zara | Ali | 2000 |
| 27 | Daisy | Das | 5000 |
| 28 | John | Paul | 5000 |
| 29 | Mohd | Yasee | 3000 |
+----+------------+-----------+--------+
4 rows in set (0.00 sec)
