java框架之Hibernate(4)-几种检索方式
准备
模型及映射文件
package com.zze.bean; import java.util.HashSet; import java.util.Set; public class Class { public Class() { } public Class(Integer id, String name) { this.id = id; this.name = name; } private Integer id; private String name; private Set<Student> students = new HashSet<>(); 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 Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } @Override public String toString() { return "Class{" + "id=" + id + ", name='" + name + '\'' + '}'; } }
班级模型:com.zze.bean.Class
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.zze.bean.Class" table="class"> <id name="id"> <generator class="native"/> </id> <property name="name" length="32"/> <set name="students" cascade="save-update"> <key column="cid"/> <one-to-many class="com.zze.bean.Student"/> </set> </class> </hibernate-mapping>
班级映射:com/zze/bean/Class.hbm.xml
package com.zze.bean; import java.util.Date; import java.util.HashSet; import java.util.Set; public class Student { public Student() { } public Student(Integer id, String name, Integer age,String gender) { this.id = id; this.name = name; this.age = age; this.gender = gender; } private Integer id; private String name; private Integer age; private String gender; private Class clazz; 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 Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } public Class getClazz() { return clazz; } public void setClazz(Class clazz) { this.clazz = clazz; } @Override public String toString() { return "Student{" + "id=" + id + ", name='" + name + '\'' + '}'; } }
学生模型:com.zze.bean.Student
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.zze.bean.Student" table="student"> <id name="id"> <generator class="native"/> </id> <property name="name" length="32"/> <property name="age"/> <property name="gender"/> <many-to-one name="clazz" column="cid" class="com.zze.bean.Class"/> </class> </hibernate-mapping>
学生映射:com/zze/bean/Student.hbm.xml
全局配置
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.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.url">jdbc:mysql://192.168.208.153:3306/1221</property> <property name="hibernate.connection.username">root</property> <property name="hibernate.connection.password">root</property> <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property> <property name="hibernate.show_sql">true</property> <property name="hibernate.format_sql">true</property> <property name="current_session_context_class">thread</property> <property name="hibernate.hbm2ddl.auto">create</property> <mapping resource="com/zze/bean/Class.hbm.xml"></mapping> <mapping resource="com/zze/bean/Student.hbm.xml"></mapping> </session-factory> </hibernate-configuration>
hibernate.cfg.xml
工具类
package com.zze.util; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.cfg.Configuration; public class HibernateUtil { public static final Configuration cfg; public static final SessionFactory sf; static { cfg = new Configuration().configure(); sf = cfg.buildSessionFactory(); } public static Session openSession() { return sf.openSession(); } public static Session getCurrentSession() { return sf.getCurrentSession(); } }
com.zze.util.HibernateUtil
初始化数据
@Test public void initData(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz1 = new Class(null,"软件一班"); Class clazz2 = new Class(null,"软件二班"); Class clazz3 = new Class(null,"汽修一班"); Class clazz4 = new Class(null,"汽修二班"); Student student1 = new Student(null, "张三", 12,"男"); Student student2 = new Student(null, "李四", 13,"女"); Student student3 = new Student(null, "王五", 14,"男"); Student student4 = new Student(null, "赵六", 15,"男"); Student student5 = new Student(null, "吴刚", 39,"男"); Student student6 = new Student(null, "王如花", 30,"女"); Student student7 = new Student(null, "李志静", 49,"女"); Student student8 = new Student(null, "何王天", 30,"男"); clazz1.getStudents().add(student1); clazz1.getStudents().add(student2); clazz2.getStudents().add(student3); clazz2.getStudents().add(student4); clazz3.getStudents().add(student5); clazz3.getStudents().add(student6); clazz4.getStudents().add(student7); clazz4.getStudents().add(student8); session.save(clazz1); session.save(clazz2); session.save(clazz3); session.save(clazz4); transaction.commit(); }
init data
几种检索方式
OID检索
简介
Hibernate 根据对象的 OID(主键)进行检索。
示例
@Test public void test1(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1); System.out.println(clazz); transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=1, name='软件一班'} */ }
例 1:使用 get 方法
@Test public void test2() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.load(Class.class, 1); System.out.println(clazz); transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=1, name='软件一班'} */ }
例 2:使用 load 方法
对象导航检索
简介
Hibernate 根据一个已经查询到的对象,获得其关联的对象的一种查询方式。
示例
@Test public void test3(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.load(Class.class, 1); System.out.println(clazz); System.out.println(Arrays.toString(clazz.getStudents().toArray())); transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=1, name='软件一班'} Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? [Student{id=2, name='张三'}, Student{id=1, name='李四'}] */ }
例 3:
HQL检索
简介
Hibernate Language Query,Hibernate 本身提供语法支持的一种检索方式。
示例
/** * 查询所有班级 */ @Test public void test4(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql ="from Class"; Query query = session.createQuery(hql); List<Class> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select class0_.id as id1_0_, class0_.name as name2_0_ from class class0_ [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}] */ }
例 4:简单查询
@Test public void test5(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql ="select c from Class c"; Query query = session.createQuery(hql); List<Class> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select class0_.id as id1_0_, class0_.name as name2_0_ from class class0_ [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}] */ }
例 5:别名查询
/** * 根据年龄排序 */ @Test public void test6(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); // 升序 String hql = "from Student order by age"; // 降序 // String hql = "from Student order by age desc"; Query query = session.createQuery(hql); List<Class> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select student0_.id as id1_1_, student0_.name as name2_1_, student0_.age as age3_1_, student0_.gender as gender4_1_, student0_.cid as cid5_1_ from student student0_ order by student0_.age [Student{id=2, name='张三'}, Student{id=1, name='李四'}, Student{id=3, name='王五'}, Student{id=4, name='赵六'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}, Student{id=5, name='吴刚'}, Student{id=7, name='李志静'}] */ }
例 6:排序查询
/** * 一个条件,查询 name='张三' 的 Student * 参数按位置绑定 */ @Test public void test7() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "from Student where name = ?"; Query query = session.createQuery(hql); query.setParameter(0, "张三"); List<Student> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select student0_.id as id1_1_, student0_.name as name2_1_, student0_.age as age3_1_, student0_.gender as gender4_1_, student0_.cid as cid5_1_ from student student0_ where student0_.name=? [Student{id=2, name='张三'}] */ } /** * 多个条件 查询 name 中包含 '王' 且 age 大于 18 的Student * 参数按名称绑定 */ @Test public void test8() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "from Student where name like :name and age>:age"; Query query = session.createQuery(hql); query.setParameter("name", "%王%"); query.setParameter("age", 18); List<Student> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select student0_.id as id1_1_, student0_.name as name2_1_, student0_.age as age3_1_, student0_.gender as gender4_1_, student0_.cid as cid5_1_ from student student0_ where ( student0_.name like ? ) and student0_.age>? [Student{id=6, name='王如花'}, Student{id=8, name='何王天'}] */ }
例 7:条件查询
/** * 查询单个属性 返回 Object List */ @Test public void test9() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "select s.name from Student s"; Query query = session.createQuery(hql); List<Object> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select student0_.name as col_0_0_ from student student0_ [李四, 张三, 王五, 赵六, 吴刚, 王如花, 李志静, 何王天] */ } /** * 查询多个属性 返回 Object[] List */ @Test public void test10() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "select s.name,s.age from Student s"; Query query = session.createQuery(hql); List<Object[]> list = query.list(); for (Object[] objects : list) { System.out.println(Arrays.toString(objects)); } transaction.commit(); /* Hibernate: select student0_.name as col_0_0_, student0_.age as col_1_0_ from student student0_ [李四, 13] [张三, 12] [王五, 14] [赵六, 15] [吴刚, 39] [王如花, 30] [李志静, 49] [何王天, 30] */ } /** * 查询多个属性 返回对应对象类型 List */ @Test public void test11() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); /* 需要让模型提供对应构造: public Student(String name, Integer age) { this.name = name; this.age = age; } */ String hql = "select new Student(name,age) from Student"; Query query = session.createQuery(hql); List<Student> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select student0_.name as col_0_0_, student0_.age as col_1_0_ from student student0_ [Student{id=null, name='李四'}, Student{id=null, name='张三'}, Student{id=null, name='王五'}, Student{id=null, name='赵六'}, Student{id=null, name='吴刚'}, Student{id=null, name='王如花'}, Student{id=null, name='李志静'}, Student{id=null, name='何王天'}] */ }
例 8:投影查询
@Test public void test12() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "from Student"; Query query = session.createQuery(hql); query.setFirstResult(0); // 起始行索引 query.setMaxResults(3); // 每页条数 List<Student> list = query.list(); System.out.println(list); transaction.commit(); /* Hibernate: select student0_.id as id1_1_, student0_.name as name2_1_, student0_.age as age3_1_, student0_.gender as gender4_1_, student0_.cid as cid5_1_ from student student0_ limit ? [Student{id=1, name='李四'}, Student{id=2, name='张三'}, Student{id=3, name='王五'}] Process finished with exit code 0 */ }
例 9:分页查询
/** * 聚合查询 */ @Test public void test13() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); // 聚合函数使用 count max min avg sum String hql = "select count(1) from Student"; Query query = session.createQuery(hql); Object o = query.uniqueResult(); System.out.println(o.getClass()); System.out.println(o); transaction.commit(); /* Hibernate: select count(1) as col_0_0_ from student student0_ class java.lang.Long 8 */ } /** * 分组查询 返回 Object[] List * 根据 gender 分组,查询每个 gender 的对应数据条数 */ @Test public void test14() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "select gender,count(1) from Student group by gender"; Query query = session.createQuery(hql); List<Object[]> list = query.list(); for (Object[] objects : list) { System.out.println(Arrays.toString(objects)); } transaction.commit(); /* Hibernate: select student0_.gender as col_0_0_, count(1) as col_1_0_ from student student0_ group by student0_.gender [女, 3] [男, 5] */ }
例 10:聚合及分组统计查询
@Test public void test23() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "from Student c join c.clazz"; Query query = session.createQuery(hql); List<Object[]> list = query.list(); for (Object[] objects : list) { System.out.println(Arrays.toString(objects)); } transaction.commit(); /* Hibernate: select student0_.id as id1_1_0_, class1_.id as id1_0_1_, student0_.name as name2_1_0_, student0_.age as age3_1_0_, student0_.gender as gender4_1_0_, student0_.cid as cid5_1_0_, class1_.name as name2_0_1_ from student student0_ inner join class class1_ on student0_.cid=class1_.id [Student{id=1, name='李四'}, Class{id=1, name='软件一班'}] [Student{id=2, name='张三'}, Class{id=1, name='软件一班'}] [Student{id=3, name='王五'}, Class{id=2, name='软件二班'}] [Student{id=4, name='赵六'}, Class{id=2, name='软件二班'}] [Student{id=5, name='吴刚'}, Class{id=3, name='汽修一班'}] [Student{id=6, name='王如花'}, Class{id=3, name='汽修一班'}] [Student{id=7, name='李志静'}, Class{id=4, name='汽修二班'}] [Student{id=8, name='何王天'}, Class{id=4, name='汽修二班'}] */ }
例 11:普通内连接
/** * 查询所有学生及其班级 */ @Test public void test24() { /* 迫切内连接 其实就是在普通的内连接 inner join 后添加关键字 fetch 将关联表数据封装到查询对象的属性中 */ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "from Student c join fetch c.clazz"; Query query = session.createQuery(hql); List<Student> list = query.list(); for (Student student : list) { System.out.println(String.format("%s %s", student, student.getClazz())); } transaction.commit(); /* Hibernate: select student0_.id as id1_1_0_, class1_.id as id1_0_1_, student0_.name as name2_1_0_, student0_.age as age3_1_0_, student0_.gender as gender4_1_0_, student0_.cid as cid5_1_0_, class1_.name as name2_0_1_ from student student0_ inner join class class1_ on student0_.cid=class1_.id Student{id=1, name='李四'} Class{id=1, name='软件一班'} Student{id=2, name='张三'} Class{id=1, name='软件一班'} Student{id=3, name='王五'} Class{id=2, name='软件二班'} Student{id=4, name='赵六'} Class{id=2, name='软件二班'} Student{id=5, name='吴刚'} Class{id=3, name='汽修一班'} Student{id=6, name='王如花'} Class{id=3, name='汽修一班'} Student{id=7, name='李志静'} Class{id=4, name='汽修二班'} Student{id=8, name='何王天'} Class{id=4, name='汽修二班'} */ } /** * 查询所有班级及属于该班级的学生 */ @Test public void test25() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String hql = "select distinct c from Class c join fetch c.students"; Query query = session.createQuery(hql); List<Class> list = query.list(); for (Class clazz : list) { System.out.println(String.format("%s %s", clazz, clazz.getStudents())); } transaction.commit(); /* Class{id=1, name='软件一班'} [Student{id=2, name='张三'}, Student{id=1, name='李四'}] Class{id=2, name='软件二班'} [Student{id=4, name='赵六'}, Student{id=3, name='王五'}] Class{id=3, name='汽修一班'} [Student{id=5, name='吴刚'}, Student{id=6, name='王如花'}] Class{id=4, name='汽修二班'} [Student{id=7, name='李志静'}, Student{id=8, name='何王天'}] */ }
例 12:迫切内连接
QBC检索
简介
Query By Criteria,条件查询,是一种更加面向对象化的查询方式。
示例
@Test public void test15(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Class.class); List<Class> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_0_0_, this_.name as name2_0_0_ from class this_ [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}] */ }
例 13:简单查询
@Test public void test16(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Class.class); // 升序 criteria.addOrder(Order.asc("id")); // 降序 // criteria.addOrder(Order.desc("id")); List<Class> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_0_0_, this_.name as name2_0_0_ from class this_ order by this_.id asc [Class{id=1, name='软件一班'}, Class{id=2, name='软件二班'}, Class{id=3, name='汽修一班'}, Class{id=4, name='汽修二班'}] */ }
例 14:排序查询
@Test public void test17() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Student.class); criteria.setFirstResult(0); // 数据起始索引 criteria.setMaxResults(2); // 每页数据条数 List<Student> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_1_0_, this_.name as name2_1_0_, this_.age as age3_1_0_, this_.gender as gender4_1_0_, this_.cid as cid5_1_0_ from student this_ limit ? [Student{id=1, name='李四'}, Student{id=2, name='张三'}] */ }
例 15:分页查询
/** * 简单 and 条件查询 * 查询 name 包含 '王' 且 age>10 */ @Test public void test18() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Student.class); // 默认多个 criteria.add 的条件是用 and 连接 criteria.add(Restrictions.like("name", "%王%")); criteria.add(Restrictions.gt("age", 10)); List<Student> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_1_0_, this_.name as name2_1_0_, this_.age as age3_1_0_, this_.gender as gender4_1_0_, this_.cid as cid5_1_0_ from student this_ where this_.name like ? and this_.age>? [Student{id=3, name='王五'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}] */ } /** * 简单 or 条件查询 * 查询 name 包含 '王' 或 name 包含 '张' */ @Test public void test19() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Student.class); // or 条件可以通过 Restrictions.or 方法实现 criteria.add(Restrictions.or(Restrictions.like("name", "%王%"), Restrictions.like("name", "%张%"))); List<Student> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_1_0_, this_.name as name2_1_0_, this_.age as age3_1_0_, this_.gender as gender4_1_0_, this_.cid as cid5_1_0_ from student this_ where ( this_.name like ? or this_.name like ? ) [Student{id=2, name='张三'}, Student{id=3, name='王五'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}] */ } /** * 复杂 and 和 or 查询 * 查询 (name 包含 '王' 且 age>10) 或 name 包含 '张' */ @Test public void test20() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Student.class); // 通过 conjunction.add 添加的条件是 and 连接 Conjunction conjunction = Restrictions.conjunction(); conjunction.add(Restrictions.like("name", "%王%")); conjunction.add(Restrictions.gt("age", 10)); // 通过 disjunction.add 添加的条件是 or 连接 Disjunction disjunction = Restrictions.disjunction(); disjunction.add(conjunction); disjunction.add(Restrictions.like("name", "%张%")); criteria.add(disjunction); List<Student> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_1_0_, this_.name as name2_1_0_, this_.age as age3_1_0_, this_.gender as gender4_1_0_, this_.cid as cid5_1_0_ from student this_ where ( ( this_.name like ? and this_.age>? ) or this_.name like ? ) [Student{id=2, name='张三'}, Student{id=3, name='王五'}, Student{id=6, name='王如花'}, Student{id=8, name='何王天'}] */ }
例 16:条件查询
/** * 聚合统计查询 * 统计男女人数及最大年龄 */ @Test public void test21() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = session.createCriteria(Student.class); /* criteria : add : 普通条件,where addOrder : 排序 setProjection : 聚合函数和 group by having */ ProjectionList projectionList = Projections.projectionList(); projectionList.add(Projections.groupProperty("gender")); projectionList.add(Projections.rowCount()); projectionList.add(Projections.max("age")); criteria.setProjection(projectionList); List<Object[]> list = criteria.list(); for (Object[] objects : list) { System.out.println(Arrays.toString(objects)); } transaction.commit(); /* Hibernate: select this_.gender as y0_, count(*) as y1_, max(this_.age) as y2_ from student this_ group by this_.gender [女, 3, 49] [男, 5, 39] */ }
例 17:聚合及分组统计查询
/** * 离线条件查询 * 查询 name 包含 '一' */ @Test public void test22(){ DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Class.class); detachedCriteria.add(Restrictions.like("name", "%一%")); Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Criteria criteria = detachedCriteria.getExecutableCriteria(session); List<Class> list = criteria.list(); System.out.println(list); transaction.commit(); /* Hibernate: select this_.id as id1_0_0_, this_.name as name2_0_0_ from class this_ where this_.name like ? [Class{id=1, name='软件一班'}, Class{id=3, name='汽修一班'}] */ }
例 18:离线条件查询
SQL检索
简介
Hibernate 支持的原生 SQL 查询。
示例
/** * 查询所有 Class,返回 Object[] List */ @Test public void test26() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String sql = "select * from class"; SQLQuery sqlQuery = session.createSQLQuery(sql); List<Object[]> list = sqlQuery.list(); for (Object[] objects : list) { System.out.println(Arrays.toString(objects)); } transaction.commit(); /* Hibernate: select * from class [1, 软件一班] [2, 软件二班] [3, 汽修一班] [4, 汽修二班] */ } /** * 查询所有 Class,返回 Class List */ @Test public void test27() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); String sql = "select * from class"; SQLQuery sqlQuery = session.createSQLQuery(sql); sqlQuery.addEntity(Class.class); List<Class> list = sqlQuery.list(); for (Class clazz : list) { System.out.println(clazz); } transaction.commit(); /* Hibernate: select * from class Class{id=1, name='软件一班'} Class{id=2, name='软件二班'} Class{id=3, name='汽修一班'} Class{id=4, name='汽修二班'} */ }
例 19:原生 SQL 查询
延迟加载
概述
只有真正使用对象的属性时才会发送 SQL 进行查询。如: session.load(Student.class,1); 。
分类
类级别的延迟加载
指的是查询某个类的对象时,针对这个类的对象是否使用延迟加载。
除了修改 lazy="false" 这种方式,还可通过如下两种方式让 lazy 失效:1、将持久化类以 final 修饰。
2、通过调用 Hibernate.initialize(proxy); 。
关联级别的延迟加载
指的是查询到某个对象后,再查询其关联的对象是否使用延迟加载。
示例
/** * 懒加载 * 修改映射文件 : * com/zze/bean/Class.hbm.xml : * <class name="com.zze.bean.Class" table="class" lazy="true"> * lazy 默认为 true */ @Test public void test27() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.load(Class.class, 1); System.out.println(clazz.getClass()); // class com.zze.bean.Class_$$_jvst718_0 System.out.println(clazz); // 发出 SQL transaction.commit(); } /** * 立即加载 * 修改映射文件 : * com/zze/bean/Class.hbm.xml : * <class name="com.zze.bean.Class" table="class" lazy="false"> */ @Test public void test28() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.load(Class.class, 1); // 发出 SQL System.out.println(clazz.getClass()); // class com.zze.bean.Class System.out.println(clazz); transaction.commit(); }
例 20:类级别的延迟加载
/** * 懒加载 * 修改映射文件 : * com/zze/bean/Class.hbm.xml : * <set name="students" cascade="save-update" lazy="true"> * lazy 默认为 true */ @Test public void test29() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1); Set<Student> students = clazz.getStudents(); System.out.println(students); // 发出 SQL transaction.commit(); } /** * 即时加载 * 修改映射文件 : * com/zze/bean/Class.hbm.xml : * <set name="students" cascade="save-update" lazy="false"> */ @Test public void test30() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1); Set<Student> students = clazz.getStudents(); // 发出 SQL System.out.println(students); transaction.commit(); } /** * 懒加载 * 修改映射文件 : * com/zze/bean/Student.hbm.xml : * <many-to-one name="clazz" lazy="proxy" column="cid" class="com.zze.bean.Class"/> * com/zze/bean/Class.hbm.xml : * <class name="com.zze.bean.Class" table="class" lazy="true"> * <p> * proxy : 默认值,表示引用关联类的加载策略。 */ @Test public void test31() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Student student = session.get(Student.class, 1); Class clazz = student.getClazz(); System.out.println(clazz); // 发出 SQL transaction.commit(); } /** * 即时加载 * 当关联类的 lazy="false" 时,无论当前类 many-to-one 标签上的 lazy 如何配置,都是即时加载。 * 修改映射文件 : * com/zze/bean/Student.hbm.xml : * * <many-to-one name="clazz" lazy="proxy" column="cid" class="com.zze. * com/zze/bean/Class.hbm.xml : * * <class name="com.zze.bean.Class" table="class" lazy="false"> * 或 : * com/zze/bean/Student.hbm.xml : * * <many-to-one name="clazz" lazy="false" column="cid" class="com.zze.bean.Class"/> * com/zze/bean/Class.hbm.xml : * * <class name="com.zze.bean.Class" table="class" lazy="true"> */ @Test public void test32() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Student student = session.get(Student.class, 1); Class clazz = student.getClazz(); // 发出 SQL System.out.println(clazz); transaction.commit(); }
例 21:关联级别的延迟加载
抓取策略
概述
通过一个对象抓取关联对象需要发送 SQL ,SQL 如何发送及 SQL 的发送规则就可以通过抓取策略进行配置。
通过 <set> 或 <many-to-one> 上的 fetch 属性进行配置。
要考虑fetch 和这些标签上的 lazy 如何配置才能最大化优化发送的 SQL 语句。
set标签上的fetch和lazy
fetch
抓取策略,控制 SQL 语句格式。
在这里 fetch 有三个可选值:
select : 默认值,发送普通 select 语句查询关联对象。
join: 发送一条迫切左外连接查询关联对象。
subselect : 发送子查询查询关联对象。
lazy
延迟加载,控制查询关联对象时是否使用懒加载。
在这里 lazy 有三个可选值:
true : 默认值,查询关联对象时,使用延迟加载。
false : 查询关联对象时,不使用延迟加载。
extra : 及其懒惰。
示例
/** * com/zze/bean/Class.hbm.xml * 默认值: * <set name="students" cascade="save-update" fetch="select" lazy="true"> */ @Test public void test33() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1); for (Student student : clazz.getStudents()) { System.out.println(student);// 发送 SQL } transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? Student{id=2, name='张三'} Student{id=1, name='李四'} */ } /** * com/zze/bean/Class.hbm.xml * * <set name="students" cascade="save-update" fetch="select" lazy="false"> */ @Test public void test34() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1); //发送 2 条 SQL for (Student student : clazz.getStudents()) { System.out.println(student); } transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? Student{id=2, name='张三'} Student{id=1, name='李四'} */ } /** * com/zze/bean/Class.hbm.xml * * <set name="students" cascade="save-update" fetch="select" lazy="extra"> */ @Test public void test35() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1); System.out.println(clazz.getStudents().size()); // 针对数量发送一条sql transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Hibernate: select count(id) from student where cid =? */ } /** * com/zze/bean/Class.hbm.xml * fetch="join" 时,lazy 失效 * <set name="students" cascade="save-update" fetch="join" lazy="true"> */ public void test36() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Class clazz = session.get(Class.class, 1);// 发送 SQL for (Student student : clazz.getStudents()) { System.out.println(student); } transaction.commit(); /* Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_, students1_.cid as cid5_1_1_, students1_.id as id1_1_1_, students1_.id as id1_1_2_, students1_.name as name2_1_2_, students1_.age as age3_1_2_, students1_.gender as gender4_1_2_, students1_.cid as cid5_1_2_ from class class0_ left outer join student students1_ on class0_.id=students1_.cid where class0_.id=? Student{id=2, name='张三'} Student{id=1, name='李四'} */ } /** * com/zze/bean/Class.hbm.xml * * <set name="students" cascade="save-update" fetch="subselect" lazy="true"> */ @Test public void test37() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Query query = session.createQuery("from Class"); List<Class> list = query.list(); for (Class clazz : list) { Set<Student> students = clazz.getStudents(); // 发送 SQL System.out.println(students); } transaction.commit(); /* Hibernate: select class0_.id as id1_0_, class0_.name as name2_0_ from class class0_ Hibernate: select students0_.cid as cid5_1_1_, students0_.id as id1_1_1_, students0_.id as id1_1_0_, students0_.name as name2_1_0_, students0_.age as age3_1_0_, students0_.gender as gender4_1_0_, students0_.cid as cid5_1_0_ from student students0_ where students0_.cid in ( select class0_.id from class class0_ ) [Student{id=1, name='李四'}, Student{id=2, name='张三'}] [Student{id=4, name='赵六'}, Student{id=3, name='王五'}] [Student{id=5, name='吴刚'}, Student{id=6, name='王如花'}] [Student{id=7, name='李志静'}, Student{id=8, name='何王天'}] */ } /** * com/zze/bean/Class.hbm.xml * * <set name="students" cascade="save-update" fetch="subselect" lazy="false"> */ @Test public void test38() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Query query = session.createQuery("from Class"); List<Class> list = query.list(); // 发送 SQL for (Class clazz : list) { Set<Student> students = clazz.getStudents(); System.out.println(students); } transaction.commit(); /* Hibernate: select class0_.id as id1_0_, class0_.name as name2_0_ from class class0_ Hibernate: select students0_.cid as cid5_1_1_, students0_.id as id1_1_1_, students0_.id as id1_1_0_, students0_.name as name2_1_0_, students0_.age as age3_1_0_, students0_.gender as gender4_1_0_, students0_.cid as cid5_1_0_ from student students0_ where students0_.cid in ( select class0_.id from class class0_ ) [Student{id=1, name='李四'}, Student{id=2, name='张三'}] [Student{id=4, name='赵六'}, Student{id=3, name='王五'}] [Student{id=5, name='吴刚'}, Student{id=6, name='王如花'}] [Student{id=7, name='李志静'}, Student{id=8, name='何王天'}] */ }
例 22:
many-to-one上的fetch和lazy
fetch
抓取策略,控制 SQL 语句格式。
在这里 fetch 有两个可选值:
select : 默认值,发送普通的 select 语句查询关联对象。
join : 发送一条迫切左外连接查询关联对象。
lazy
延迟加载,控制查询关联对象时是否使用懒加载。
在这里 lazy 有三个可选值:
proxy : 默认值,引用关联对象类的类级别加载策略。
flase : 查询关联对象时,不使用延迟加载。
no-proxy:不使用。
示例
/** * com/zze/bean/Student.hbm.xml * 默认值 * <many-to-one name="clazz" column="cid" class="com.zze.bean.Class" fetch="select" lazy="proxy"/> * * com/zze/bean/Class.hbm.xml * <class name="com.zze.bean.Class" table="class" lazy="true"> */ @Test public void test39(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Student student = session.get(Student.class, 1); System.out.println(student.getClazz()); // 发送 SQL transaction.commit(); /* Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_, student0_.age as age3_1_0_, student0_.gender as gender4_1_0_, student0_.cid as cid5_1_0_ from student student0_ where student0_.id=? Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=1, name='软件一班'} */ } /** * com/zze/bean/Student.hbm.xml * 默认值 * <many-to-one name="clazz" column="cid" class="com.zze.bean.Class" fetch="select" lazy="proxy"/> * * com/zze/bean/Class.hbm.xml * <class name="com.zze.bean.Class" table="class" lazy="false"> */ @Test public void test40(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Student student = session.get(Student.class, 1);// 一次发送 2 条 SQL System.out.println(student.getClazz()); transaction.commit(); /* Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_, student0_.age as age3_1_0_, student0_.gender as gender4_1_0_, student0_.cid as cid5_1_0_ from student student0_ where student0_.id=? Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=1, name='软件一班'} */ } /** * com/zze/bean/Student.hbm.xml * fetch="join" 时,lazy 失效 * <many-to-one name="clazz" column="cid" class="com.zze.bean.Class" fetch="join" lazy="proxy"/> */ @Test public void test41(){ Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Student student = session.get(Student.class, 1);// 一条关联 SQL System.out.println(student.getClazz()); transaction.commit(); /* Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_, student0_.age as age3_1_0_, student0_.gender as gender4_1_0_, student0_.cid as cid5_1_0_, class1_.id as id1_0_1_, class1_.name as name2_0_1_ from student student0_ left outer join class class1_ on student0_.cid=class1_.id where student0_.id=? Class{id=1, name='软件一班'} */ }
例 23:
批量抓取
一批指定数量的关联数据一起查询。
/** * 查询所有班级 及 所有班级下的学生信息 * 默认情况下,查询所有班级会发一条 SQL,然后每次查询班级上的学生也会发送一条 SQL * 即如下有 4 个班级,会发 5 条SQL */ @Test public void test42() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Query query = session.createQuery("from Class"); List<Class> list = query.list(); for (Class clazz : list) { System.out.println(clazz); for (Student student : clazz.getStudents()) { System.out.println(student); } } transaction.commit(); /* Hibernate: select class0_.id as id1_0_, class0_.name as name2_0_ from class class0_ Class{id=1, name='软件一班'} Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? Student{id=1, name='李四'} Student{id=2, name='张三'} Class{id=2, name='软件二班'} Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? Student{id=4, name='王五'} Student{id=3, name='赵六'} Class{id=3, name='汽修一班'} Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? Student{id=5, name='王如花'} Student{id=6, name='吴刚'} Class{id=4, name='汽修二班'} Hibernate: select students0_.cid as cid5_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.name as name2_1_1_, students0_.age as age3_1_1_, students0_.gender as gender4_1_1_, students0_.cid as cid5_1_1_ from student students0_ where students0_.cid=? Student{id=8, name='李志静'} Student{id=7, name='何王天'} */ } /** * com/zze/bean/Class.hbm.xml * * <set name="students" cascade="save-update" batch-size="4"> * <p> * 一次抓取 4 条,就只需要发送 2 次 SQL * 一次查询所有班级,一次查询所有班级下的学生 */ @Test public void test43() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Query query = session.createQuery("from Class"); List<Class> list = query.list(); for (Class clazz : list) { System.out.println(clazz); for (Student student : clazz.getStudents()) { System.out.println(student); } } transaction.commit(); /* Hibernate: select class0_.id as id1_0_, class0_.name as name2_0_ from class class0_ Class{id=1, name='软件一班'} Hibernate: select students0_.cid as cid5_1_1_, students0_.id as id1_1_1_, students0_.id as id1_1_0_, students0_.name as name2_1_0_, students0_.age as age3_1_0_, students0_.gender as gender4_1_0_, students0_.cid as cid5_1_0_ from student students0_ where students0_.cid in ( ?, ?, ?, ? ) Student{id=1, name='李四'} Student{id=2, name='张三'} Class{id=2, name='软件二班'} Student{id=4, name='王五'} Student{id=3, name='赵六'} Class{id=3, name='汽修一班'} Student{id=5, name='王如花'} Student{id=6, name='吴刚'} Class{id=4, name='汽修二班'} Student{id=7, name='何王天'} Student{id=8, name='李志静'} */ } /** * 查询所有学生 及 所有学生所属班级信息 * 默认情况下,查询所有学生会发送 1 条 SQL,然后每次查询每个学生的所属班级时也会发送一条 SQL, * 有 8 个学生,但一共有 4 个班级,由于一级缓存的作用,查询班级需要发送 4 条 SQL * 共发 5 条 SQL */ @Test public void test44() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Query query = session.createQuery("from Student"); List<Student> list = query.list(); for (Student student : list) { System.out.println(student.getClazz()); } transaction.commit(); /* Hibernate: select student0_.id as id1_1_, student0_.name as name2_1_, student0_.age as age3_1_, student0_.gender as gender4_1_, student0_.cid as cid5_1_ from student student0_ Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=1, name='软件一班'} Class{id=1, name='软件一班'} Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=2, name='软件二班'} Class{id=2, name='软件二班'} Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=3, name='汽修一班'} Class{id=3, name='汽修一班'} Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=4, name='汽修二班'} Class{id=4, name='汽修二班'} */ } /** * com/zze/bean/Class.hbm.xml * <class name="com.zze.bean.Class" table="class" batch-size="3"> * <p> * many-to-one 关系时需在关联属性类映射文件下配置 batch-size * <p> * 查询所有学生 1 条 SQL,查询所有班级每次抓取 3 条,一共 4 个班级,会发 2 次 SQL */ @Test public void test45() { Session session = HibernateUtil.getCurrentSession(); Transaction transaction = session.beginTransaction(); Query query = session.createQuery("from Student"); List<Student> list = query.list(); for (Student student : list) { System.out.println(student.getClazz()); } transaction.commit(); /* Hibernate: select student0_.id as id1_1_, student0_.name as name2_1_, student0_.age as age3_1_, student0_.gender as gender4_1_, student0_.cid as cid5_1_ from student student0_ Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id in ( ?, ?, ? ) Class{id=1, name='软件一班'} Class{id=1, name='软件一班'} Class{id=2, name='软件二班'} Class{id=2, name='软件二班'} Class{id=3, name='汽修一班'} Class{id=3, name='汽修一班'} Hibernate: select class0_.id as id1_0_0_, class0_.name as name2_0_0_ from class class0_ where class0_.id=? Class{id=4, name='汽修二班'} Class{id=4, name='汽修二班'} */ }
例 24:
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