Hibernate中共提供了三种检索方式:HQL(Hibernate Query Language)、QBC、QBE(Query By Example)。
HQL 是Hibernate Query Language的简写,即hibernate查询语言:HQL采用面向对象的查询方式。
QBC(Query By Criteria) API提供了检索对象的另一种方式,它主要由Criteria接口、Criterion接口和Expresson类组成,它支持在运行时动态生成查询语句。
HQL 查询包括以下步骤:
- 获取Hibernate Session对象。
- 编写HQL语句
- 以HQL语句作为参数,调用Session的createQuery方法创建查询对象。
- 如果HQL语句包含参数,则调用Query的setXxx方法为参数赋值。
- 调用Query对象的list()或uniqueResult()方法返回查询结果列表(持久化实体集)
QBC检索步骤:
1.调用Session的createCriteria()方法创建一个Criteria对象。
2.设定查询条件。Restrictions类提供了一系列用于设定查询条件的静态方法,
这些静态方法都返回Criterion实例,每个Criterion实例代表一个查询条件。
Criteria的add()方法用于加入查询条件。
3.调用Criteria的list()方法执行查询语句。该方法返回List类型的查询结果,在
List集合中存放了符合查询条件的持久化对象。
下面列出我学习的代码。
Department类
package oracle.hqlqbc; import java.util.HashSet; import java.util.Set; public class Department { private Integer id; private String name; private Set<Employee> emps = new HashSet<>(); public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } @Override public String toString() { StringBuilder builder = new StringBuilder(); builder.append("Department [id="); builder.append(id); builder.append(", name="); builder.append(name); builder.append(", empsSize="); builder.append(emps.size()); builder.append("]"); return builder.toString(); } public void setName(String name) { this.name = name; } public Set<Employee> getEmps() { return emps; } public void setEmps(Set<Employee> emps) { this.emps = emps; } }
Employee类
package oracle.hqlqbc; public class Employee { @Override public String toString() { StringBuilder builder = new StringBuilder(); builder.append("Employee [id="); builder.append(id); builder.append(", name="); builder.append(name); builder.append(", salary="); builder.append(salary); builder.append(", email="); builder.append(email); builder.append(", deptId="); builder.append(dept.getId()); builder.append("]"); return builder.toString(); } private Integer id; private String name; private float salary; private String email; private Department dept; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public float getSalary() { return salary; } public void setSalary(float salary) { this.salary = salary; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public Department getDept() { return dept; } public void setDept(Department dept) { this.dept = dept; } public Employee(float salary, String email, Department dept) { super(); this.salary = salary; this.email = email; this.dept = dept; } public Employee() { } }
Department.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2017-7-29 2:43:46 by Hibernate Tools 3.5.0.Final --> <hibernate-mapping package="oracle.test"> <class name="Department" table="DEPARTMENT"> <id name="id" type="java.lang.Integer"> <column name="ID" /> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> <set name="emps" table="EMPLOYEE" inverse="true" lazy="true"> <key><column name="DEPT_ID" /></key> <one-to-many class="Employee" /> </set> </class> </hibernate-mapping>
Employee.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated 2017-7-29 2:43:46 by Hibernate Tools 3.5.0.Final --> <hibernate-mapping package="oracle.test"> <class name="Employee" table="EMPLOYEE"> <id name="id" type="java.lang.Integer"> <column name="ID" /> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> <property name="salary" type="float"> <column name="SALARY" /> </property> <property name="email" type="java.lang.String"> <column name="EMAIL" /> </property> <many-to-one name="dept" class="Department" fetch="join"><!-- join select subselect--> <column name="DEPT_ID" /> </many-to-one> </class> <query name="salaryEmps"><![CDATA[FROM Employee e WHERE e.salary > :minSal AND e.salary < :maxSal]]></query> </hibernate-mapping>
具体用法的例子:
package oracle.hqlqbc; import java.util.Arrays; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Query; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; import org.hibernate.criterion.Conjunction; import org.hibernate.criterion.Disjunction; import org.hibernate.criterion.MatchMode; import org.hibernate.criterion.Order; import org.hibernate.criterion.Projection; import org.hibernate.criterion.Projections; import org.hibernate.criterion.Restrictions; import org.hibernate.service.ServiceRegistry; import org.hibernate.service.ServiceRegistryBuilder; import org.junit.After; import org.junit.Before; import org.junit.Test; import oracle.hqlqbc.Department; import oracle.hqlqbc.Employee; public class HibernateTest { private SessionFactory sessionFactory; private Session session; private Transaction transaction; @Before public void init() { System.out.println("init"); // 1. 创建一个SessionFactory对象 sessionFactory = null; Configuration configuration = new Configuration().configure(); // before 4.0 // sessionFactory = configuration.buildSessionFactory(); ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()) .buildServiceRegistry(); sessionFactory = configuration.buildSessionFactory(serviceRegistry); // 2. 创建一个Session 对象 session = sessionFactory.openSession(); // 3. 开启事务 transaction = session.beginTransaction(); } @After public void destory() { System.out.println("destory"); // 5. 提交事务 transaction.commit(); // 6. 关闭Session session.close(); // 7. 关闭SesssionFactory sessionFactory.close(); } @Test public void testNamedParameter() { String hql = "FROM Employee e WHERE e.salary > :sal AND e.email LIKE :email"; Query query = session.createQuery(hql); // 可以用命名参数 query.setFloat("sal", 7000) .setString("email", "%A%"); List<Employee> emps = query.list(); System.out.println(emps.size()); } @Test public void createTable() { } @Test public void testHQL() { // 1. 创建Query对象: 可以加 ORDER BY String hql = "FROM Employee e WHERE e.salary > ? AND e.email LIKE ? AND dept = ? ORDER BY e.salary"; Query query = session.createQuery(hql); // 2. 绑定参数 // Query对象调用setXxx方法支持方法链的编程风格 Department dept = new Department(); dept.setId(80); // 可以用方法链 query.setFloat(0, 6000).setString(1, "%A%"); // 可用用实体 query.setEntity(2, dept); // 3. 执行查询 List<Employee> employees = query.list(); System.out.println(employees.size()); } /* * 分页查询 */ @Test public void testPageQuery() { String hql = "FROM Employee"; Query query = session.createQuery(hql); int pageNo = 3; int pageSize = 5; List<Employee> emps = query.setFirstResult((pageNo - 1)* pageSize) .setMaxResults(pageSize).list(); System.out.println(emps); } /* * 命名查询 */ @Test public void namedQuery() { Query query = session.getNamedQuery("salaryEmps"); List<Employee> emps = query.setFloat("minSal", 5000) .setFloat("maxSal", 10000) .list(); System.out.println(emps.size()); } /* * 投影查询1: 操作数组 */ @Test public void testPropertyQuery() { String hql = "SELECT e.email, e.salary FROM Employee e where e.dept = :dept"; Query query = session.createQuery(hql); Department dept = new Department(); dept.setId(80); List<Object[]> result = query.setEntity("dept", dept) .list(); for(Object[] objs: result) { System.out.println(Arrays.asList(objs)); } } /* * 投影查询2: 操作entity:使用构造器 */ @Test public void testPropertyQuery2() { String hql = "SELECT new Employee(e.salary, e.email, e.dept) FROM Employee e where e.dept = :dept"; Query query = session.createQuery(hql); Department dept = new Department(); dept.setId(80); List<Employee> result = query.setEntity("dept", dept).list(); for(Employee emp: result) { System.out.println(emp.getId() + ", " + emp.getEmail() + ", " + emp.getSalary() + ", " + emp.getDept()); } } /* * 报表查询: 可以使用聚合函数 */ @Test public void testGroupBy() { String hql = "SELECT min(e.salary), max(e.salary) FROM Employee e " + "group by e.dept having min(salary) > :minSal"; Query query = session.createQuery(hql).setFloat("minSal", 5000); List<Object[]> result = query.list(); for(Object[] objs: result) { System.out.println(Arrays.asList(objs)); } } /* * HQL 会忽略配置文件中的fetch=join的设置,如果想用,就在代码中直接写 * 迫切左外连接:返回department,注意去重 */ @Test public void testLeftJoinFetch() { String hql = "SELECT DISTINCT d FROM Department d INNER JOIN FETCH d.emps"; Query query = session.createQuery(hql); // 集合去重 // new ArrayList<>(new HashSet<>(Collection c)); List<Department> depts = query.list(); System.out.println(depts.size()); for(Department dept: depts) { System.out.println(dept.getName() + ", " + dept.getEmps().size()); } } /* * 默认返回对象数组,注意去重, */ @Test public void testLeftJoin() { // 这样返回的Employee未被初始化 String hql = "SELECT DISTINCT d FROM Department d LEFT JOIN d.emps"; Query query = session.createQuery(hql); /*List<Object[]> result = query.list(); System.out.println(result); for(Object[] objs: result) { System.out.println(Arrays.asList(objs)); }*/ List<Department> depts = query.list(); System.out.println(depts.size()); for(Department dept: depts) { System.out.println(dept.getName()); } } @Test public void testLeftJoinFetch2() { String hql = "SELECT e FROM Employee e INNER JOIN FETCH e.dept"; Query query = session.createQuery(hql); List<Employee> emps = query.list(); System.out.println(emps.size()); for(Employee emp: emps) { System.out.println(emp.getName() + ", " + emp.getDept().getName()); } } @Test public void testQBCQuery() { Criteria criteria = session.createCriteria(Employee.class); criteria.add(Restrictions.eq("email", "SKUMAR")); criteria.add(Restrictions.gt("salary", 5000f)); Employee employee = (Employee) criteria.uniqueResult(); System.out.println(employee); } @Test public void testQBCQuery2() { Criteria criteria = session.createCriteria(Employee.class); // 1. AND: 使用Conjunction表示,本身就是一个Criterion对象 // 且其中还可以添加Criterion对象 Conjunction conjunction = Restrictions.conjunction(); conjunction.add(Restrictions.like("name", "a", MatchMode.ANYWHERE)); Department dept = new Department(); dept.setId(80); conjunction.add(Restrictions.eq("dept", dept)); System.out.println(conjunction); // or Disjunction disjunction = Restrictions.disjunction(); disjunction.add(Restrictions.ge("salary", 6000)); disjunction.add(Restrictions.isNotNull("email")); criteria.add(conjunction); criteria.add(disjunction); criteria.list(); } @Test public void testQBCQuery3() { Criteria criteria = session.createCriteria(Employee.class); // 统计查询 criteria.setProjection(Projections.max("salary")); System.out.println(criteria.uniqueResult()); } @Test public void testQBCQuery4() { Criteria criteria = session.createCriteria(Employee.class); criteria.addOrder(Order.asc("salary")); criteria.addOrder(Order.desc("email")); int pageSize = 5; int pageNo = 3; criteria.setFirstResult((pageNo - 1) * pageSize) .setMaxResults(pageSize).list(); } @Test public void testNativeSQL() { String sql = "INSERT INTO department VALUES(?, ?)"; Query query = session.createSQLQuery(sql); query.setInteger(0, 280) .setString(1, "ATGUIGU") .executeUpdate(); } @Test public void testHQLUpdate() { String hql = "DELETE FROM Department d where d.id = :id"; session.createQuery(hql).setInteger("id", 280).executeUpdate(); } }
好了,例子都在上面,自己也复习了一遍,有了一个初步的印象,本文仅供入门了解,更深入的内容查看相关文章学习。
原文地址:https://www.cnblogs.com/liunianfeiyu/p/8722154.html
时间: 2024-10-14 08:19:59