Hibernate实战——投影聚合和分组

喜欢ヅ旅行 2021-07-24 13:04 434阅读 0赞

**一 配置**

<?xml version="1.0" encoding="GBK"?>
    
    <!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="connection.driver_class">com.mysql.jdbc.Driver</property>
               
               <property  name="connection.url">jdbc:mysql://localhost/hibernate</property>
               
               <property name="connection.username">root</property>
               
               <property name="connection.password">32147</property>
               
               <property  name="hibernate.c3p0.max_size">200</property>
               
               <property name="hibernate.c3p0.min_size">2</property>
               
               <property  name="hibernate.c3p0.timeout">5000</property>
               
               <property  name="hibernate.c3p0.max_statements">100</property>
               <property  name="hibernate.c3p0.idle_test_period">3000</property>
               <property  name="hibernate.c3p0.acquire_increment">2</property>
               <property  name="hibernate.c3p0.validate">true</property>
               
               <property  name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
               
               <property name="hbm2ddl.auto">update</property>
               
               <property name="show_sql">true</property>
               
               <property name="hibernate.format_sql">true</property>
               
               <mapping class="org.crazyit.app.domain.Enrolment"/>
               <mapping class="org.crazyit.app.domain.Student"/>
               <mapping class="org.crazyit.app.domain.Course"/>
         </session-factory>
    </hibernate-configuration>

**二 PO**

Student

package org.crazyit.app.domain;
    
    import java.util.*;
    import javax.persistence.*;
    
    @Entity
    @Table(name="student_inf")
    public class Student
    {
        // 代表学生学号的成员变量，将作为标识属性
        @Id @Column(name="student_id")
        private Integer studentNumber;
        // 代表学生姓名的成员变量
        private String name;
        // 该学生的所有选课记录对应的关联实体
        @OneToMany(targetEntity=Enrolment.class
            , mappedBy="student" , cascade=CascadeType.REMOVE)
        private Set<Enrolment> enrolments
            = new HashSet<>();
    
        // 无参数的构造器
        public Student()
        {
        }
        // 初始化全部成员变量的构造器
        public Student(Integer studentNumber , String name)
        {
            this.studentNumber = studentNumber;
            this.name = name;
        }
    
        // studentNumber的setter和getter方法
        public void setStudentNumber(Integer studentNumber)
        {
            this.studentNumber = studentNumber;
        }
        public Integer getStudentNumber()
        {
            return this.studentNumber;
        }
    
        // name的setter和getter方法
        public void setName(String name)
        {
            this.name = name;
        }
        public String getName()
        {
            return this.name;
        }
    
        // enrolments的setter和getter方法
        public void setEnrolments(Set<Enrolment> enrolments)
        {
            this.enrolments = enrolments;
        }
        public Set<Enrolment> getEnrolments()
        {
            return this.enrolments;
        }
    }

Enrolment

package org.crazyit.app.domain;
    import javax.persistence.*;
    
    @Entity
    @Table(name = "enrolment_inf")
    public class Enrolment
    {
         // 定义标识属性
         @Id
         @Column(name = "enrolment_id")
         @GeneratedValue(strategy = GenerationType.IDENTITY)
         private Integer enrolmentId;
         // 定义选课记录所属的学年
         private int year;
         // 定义选课记录所属的学期
         private int semester;
         // 定义选课记录关联的学生实体
         @ManyToOne(targetEntity = Student.class)
         @JoinColumn(name = "student_id")
         private Student student;
         // 定义选课记录关联的课程实体
         @ManyToOne(targetEntity = Course.class)
         @JoinColumn(name = "course_code")
         private Course course;
         // enrolmentId的setter和getter方法
         public void setEnrolmentId(Integer enrolmentId) {
               this.enrolmentId = enrolmentId;
         }
         public Integer getEnrolmentId() {
               return this.enrolmentId;
         }
         // year的setter和getter方法
         public void setYear(int year) {
               this.year = year;
         }
         public int getYear() {
               return this.year;
         }
         // semester的setter和getter方法
         public void setSemester(int semester) {
               this.semester = semester;
         }
         public int getSemester() {
               return this.semester;
         }
         // student的setter和getter方法
         public void setStudent(Student student) {
               this.student = student;
         }
         public Student getStudent() {
               return this.student;
         }
         // course的setter和getter方法
         public void setCourse(Course course) {
               this.course = course;
         }
         public Course getCourse() {
               return this.course;
         }
    }

Course

package org.crazyit.app.domain;
    import javax.persistence.*;
    
    @Entity
    @Table(name="course_inf")
    public class Course
    {
         // 代表课程编号的成员变量，将作为标识属性
         @Id @Column(name="course_code")
         private String courseCode;
         // 代表课程名成员变量
         private String name;
         // 无参数的构造器
         public Course()
         {
         }
         // 初始化全部成员变量的构造器
         public Course(String courseCode , String name)
         {
               this.courseCode = courseCode;
               this.name = name;
         }
         // courseCode的setter和getter方法
         public void setCourseCode(String courseCode)
         {
               this.courseCode = courseCode;
         }
         public String getCourseCode()
         {
               return this.courseCode;
         }
         // name的setter和getter方法
         public void setName(String name)
         {
               this.name = name;
         }
         public String getName()
         {
               return this.name;
         }
    }

**三 测试**

1 工具类

package lee;
    
    import org.hibernate.*;
    import org.hibernate.cfg.*;
    import org.hibernate.service.*;
    import org.hibernate.boot.registry.*;
    
    public class HibernateUtil
    {
        public static final SessionFactory sessionFactory;
    
        static
        {
            try
            {
                // 使用默认的hibernate.cfg.xml配置文件创建Configuration实例
                Configuration cfg = new Configuration()
                    .configure();
                // 以Configuration实例来创建SessionFactory实例
                ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
                    .applySettings(cfg.getProperties()).build();
                sessionFactory = cfg.buildSessionFactory(serviceRegistry);
            }
            catch (Throwable ex)
            {
                System.err.println("Initial SessionFactory creation failed." + ex);
                throw new ExceptionInInitializerError(ex);
            }
        }
    
        // ThreadLocal可以隔离多个线程的数据共享，因此不再需要对线程同步
        public static final ThreadLocal<Session> session
            = new ThreadLocal<Session>();
    
        public static Session currentSession()
            throws HibernateException
        {
            Session s = session.get();
            // 如果该线程还没有Session,则创建一个新的Session
            if (s == null)
            {
                s = sessionFactory.openSession();
                // 将获得的Session变量存储在ThreadLocal变量session里
                session.set(s);
            }
            return s;
        }
    
        public static void closeSession()
            throws HibernateException
        {
            Session s = session.get();
            if (s != null)
                s.close();
            session.set(null);
        }
    }

2 测试类

package lee;
    
    import org.hibernate.*;
    import org.hibernate.criterion.*;
    
    import java.util.*;
    
    import org.crazyit.app.domain.*;
    
    
    public class ProjectionTest
    {
        public static void main(String[] args)
        {
            ProjectionTest pt = new ProjectionTest();
            System.out.println("================================================================================");
            pt.query();
            System.out.println("================================================================================");
            pt.aliasQuery();
            System.out.println("================================================================================");
            pt.aliasQuery2();
            System.out.println("================================================================================");
            pt.aliasQuery3();
            System.out.println("================================================================================");
            pt.queryForProperty();
            System.out.println("================================================================================");
            pt.queryForProperty2();
            System.out.println("================================================================================");
            HibernateUtil.sessionFactory.close();
        }
    
        private void query()
        {
            // 打开Session和事务
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            // 使用createCriteria开始条件查询
            List list = session.createCriteria(Enrolment.class)
                .createAlias("student", "s")
                .setProjection(Projections.projectionList()
                    // 统计记录条数
                    .add(Projections.rowCount())
                    // 统计选择该课程里最大的学生姓名
                    .add(Projections.max("s.name"))
                    // 按course进行分组
                    .add(Projections.groupProperty("course"))
                ).list();
            for(Object ele : list)
            {
                Object[] objs = (Object[])ele;
                Course c = (Course)objs[2];
                System.out.println("=====<" + c.getName()
                    + ">课程的选课统计=====");
                System.out.println("选课人数:" + objs[0]);
                System.out.println("选课的姓名最大的学生为：" + objs[1]);
            }
            tx.commit();
            HibernateUtil.closeSession();
        }
    
    
        private void aliasQuery()
        {
            // 打开Session和事务
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            List list = session.createCriteria(Enrolment.class)
                .setProjection(Projections.projectionList()
                // 按course进行分组
                .add(Projections.groupProperty("course"))
                // 统计记录条数，并为统计结果指定别名c
                .add(Projections.alias(Projections.rowCount(), "c")))
                .addOrder(Order.asc("c"))
                .list();
            for(Object ele : list)
            {
                System.out.println(java.util.Arrays.toString((Object[])ele));
            }
            tx.commit();
            HibernateUtil.closeSession();
        }
    
        private void aliasQuery2()
        {
            // 打开Session和事务
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            List list = session.createCriteria(Enrolment.class)
                .setProjection(Projections.projectionList()
                // 按course进行分组，并为分组结果指定别名c
                .add(Projections.groupProperty("course").as("c"))
                // 统计记录条数
                .add(Projections.rowCount()))
                .addOrder(Order.asc("c"))
                .list();
            for(Object ele : list)
            {
                System.out.println(java.util.Arrays.toString((Object[])ele));
            }
            tx.commit();
            HibernateUtil.closeSession();
        }
    
        private void aliasQuery3()
        {
            // 打开Session和事务
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            List list = session.createCriteria(Enrolment.class)
                .setProjection(Projections.projectionList()
                // 按course进行分组，指定别名为c
                .add(Projections.groupProperty("course") , "c")
                // 统计每组记录的条数，指定别名为rc
                .add(Projections.rowCount(), "rc"))
                .addOrder(Order.asc("rc"))
                .list();
            for (Object ele : list)
            {
                System.out.println(java.util.Arrays.toString((Object[])ele));
            }
            tx.commit();
            HibernateUtil.closeSession();
        }
    
        private void queryForProperty()
        {
            // 打开Session和事务
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            // 使用Property只选出指定列
            List list = session.createCriteria(Student.class)
                .setProjection(Property.forName("name"))
                .list();
            for (Object ele : list)
            {
                System.out.println(ele);
            }
            tx.commit();
            HibernateUtil.closeSession();
        }
    
        private void queryForProperty2()
        {
            // 打开Session和事务
            Session session = HibernateUtil.currentSession();
            Transaction tx = session.beginTransaction();
            // 使用Property选出指定列，并根据指定列过滤数据
            List list = session.createCriteria(Enrolment.class)
                .createAlias("student", "s")
                .setProjection(Projections.projectionList()
                .add(Property.forName("course"))
                .add(Property.forName("s.name")))
                .add(Property.forName("s.name").eq("孙悟空"))       // ①
                .list();
            for (Object ele : list)
            {
                System.out.println(java.util.Arrays.toString((Object[])ele));
            }
            tx.commit();
            HibernateUtil.closeSession();
        }
    }

**四 数据脚本**

drop database if exists hibernate;
    
    create database hibernate;
    
    use hibernate;
    
    CREATE TABLE course_inf (
      course_code varchar(255) NOT NULL,
      name varchar(255) default NULL,
      PRIMARY KEY  (course_code)
    );
    
    INSERT INTO course_inf VALUES
    ('001','疯狂Java讲义'),
    ('002','轻量级Java EE企业应用实战'),
    ('003','疯狂Android讲义');
    
    CREATE TABLE student_inf (
      student_id int NOT NULL,
      name varchar(255) NOT NULL,
      PRIMARY KEY  (student_id)
    );
    
    INSERT INTO student_inf VALUES
    (20050231,'孙悟空'),
    (20050232,'猪八戒'),
    (20050233,'牛魔王');
    
    
    
    CREATE TABLE enrolment_inf (
      enrolment_id int(11) NOT NULL auto_increment,
      semester int(11) NOT NULL,
      year int(11) NOT NULL,
      student_id int default NULL,
      course_code varchar(255) default NULL,
      PRIMARY KEY  (enrolment_id),
      KEY FKEB4882C47EDE09EE (course_code),
      KEY FKEB4882C4109881D8 (student_id),
      FOREIGN KEY (student_id) REFERENCES student_inf (student_id),
      FOREIGN KEY (course_code) REFERENCES course_inf (course_code)
    );
    
    INSERT INTO enrolment_inf VALUES
    (1,3,2005,20050232,'001'),
    (2,2,2005,20050232,'003'),
    (3,2,2005,20050233,'002'),
    (4,3,2005,20050233,'003'),
    (5,1,2005,20050231,'002');

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

**五 测试**

Hibernate:
        select
            count(*) as y0_,
            max(s1_.name) as y1_,
            this_.course_code as y2_
        from
            enrolment_inf this_
        inner join
            student_inf s1_
                on this_.student_id=s1_.student_id
        group by
            this_.course_code
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    =====<疯狂Java讲义>课程的选课统计=====
    选课人数:1
    选课的姓名最大的学生为：猪八戒
    =====<轻量级Java EE企业应用实战>课程的选课统计=====
    选课人数:2
    选课的姓名最大的学生为：牛魔王
    =====<疯狂Android讲义>课程的选课统计=====
    选课人数:2
    选课的姓名最大的学生为：猪八戒
    ================================================================================
    Hibernate:
        select
            this_.course_code as y0_,
            count(*) as y1_
        from
            enrolment_inf this_
        group by
            this_.course_code
        order by
            y1_ asc
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    [org.crazyit.app.domain.Course@7e3181aa, 1]
    [org.crazyit.app.domain.Course@a22cb6a, 2]
    [org.crazyit.app.domain.Course@17aad511, 2]
    ================================================================================
    Hibernate:
        select
            this_.course_code as y0_,
            count(*) as y1_
        from
            enrolment_inf this_
        group by
            this_.course_code
        order by
            y0_ asc
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    [org.crazyit.app.domain.Course@530712d, 1]
    [org.crazyit.app.domain.Course@50468873, 2]
    [org.crazyit.app.domain.Course@6d3c5255, 2]
    ================================================================================
    Hibernate:
        select
            this_.course_code as y0_,
            count(*) as y1_
        from
            enrolment_inf this_
        group by
            this_.course_code
        order by
            y1_ asc
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    [org.crazyit.app.domain.Course@2654635, 1]
    [org.crazyit.app.domain.Course@4ce7fffa, 2]
    [org.crazyit.app.domain.Course@635572a7, 2]
    ================================================================================
    Hibernate:
        select
            this_.name as y0_
        from
            student_inf this_
    孙悟空
    猪八戒
    牛魔王
    ================================================================================
    Hibernate:
        select
            this_.course_code as y0_,
            s1_.name as y1_
        from
            enrolment_inf this_
        inner join
            student_inf s1_
                on this_.student_id=s1_.student_id
        where
            s1_.name=?
    Hibernate:
        select
            course0_.course_code as course_c1_0_0_,
            course0_.name as name2_0_0_
        from
            course_inf course0_
        where
            course0_.course_code=?
    [org.crazyit.app.domain.Course@63a270c9, 孙悟空]
    ================================================================================

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