hibernate之条件查询

Posted 2020-09-09 code.world

一、条件查询简介

条件查询是更据面向对象特色的数据查询方式，主要通过如下3个类完成

1、Criteria：代表一次查询

2、Criterion：代表一个查询条件

3、Restrictions：产生查询条件的工具类

执行条件查询的步骤

1、获取Hibernate session对象

2、调用session的createCriteria()方法创建Criteria查询对象

3、使用Restrictions的静态方法创建Criterion查询条件

4、通过Criteria的add()方法添加查询条件到Criteria查询中

5、执行Criteria的list()或uniqueResult()方法返回结果集

二、条件查询

1、整表查询

　　　　　　  Criteria c = session.createCriteria(CriteriaTeacher.class);
            List<CriteriaTeacher> list = c.list();
            for (CriteriaTeacher t : list) System.out.println(t.getName());

2、加入查询条件（通过Criteria的add()方法和Restrictions的静态方法添加）

Criteria c = session.createCriteria(CriteriaTeacher.class).add(Restrictions.like("name", "%1%"));
            List<CriteriaTeacher> list = c.list();
            for (CriteriaTeacher t : list) System.out.println(t.getName());

3、关联查询（前提持久化类内部有映射关系）

 如果需要使用关联实体的属性来增加查询条件，则需再次使用createCriteria()方法

a、默认链接方式

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .add(Restrictions.like("name", "%1%"))
                    .createCriteria("criteriaTeacher")
　　　　　　　　　　　　//.createCriteria("criteriaTeacher", "ct")//为关联实体指定别名
                    .add(Restrictions.like("name", "%1%"));
            List<CriteriaStudent> list = c.list();
            for (CriteriaStudent s : list)
                System.out.println("studentName = " + s.getName() + " | teacherName = " + s.getCriteriaTeacher().getName());

b、指定链接方式

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .add(Restrictions.like("name", "%1%"))
                    .createCriteria("criteriaTeacher", JoinType.LEFT_OUTER_JOIN);//左连接方式
            List<CriteriaStudent> list = c.list();
            for (CriteriaStudent s : list)
                System.out.println("studentName = " + s.getName() + " | teacherName = " + s.getCriteriaTeacher().getName());

 c、也可以使用createAlias（）方法代替createCriteria（）方法

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .add(Restrictions.like("name", "%1%"))
                    .createAlias("criteriaTeacher", "ct")
                    .add(Restrictions.like("ct.name", "%1%"));
            List<CriteriaStudent> list = c.list();
            for (CriteriaStudent s : list)
                System.out.println("studentName = " + s.getName() + " | teacherName = " + s.getCriteriaTeacher().getName());

4、投影、聚合、分组查询

hibernate中使用Projection接口代表投影运算，hibernate通过Criteria的setProjection(Projections p)方法进行投影运算，其中Projections作为产生Projection的工厂。

a、投影运算查询

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Projections.rowCount()));//统计表中记录条数
            System.out.println(c.uniqueResult());

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Projections.count("name"))
                    .add(Projections.groupProperty("name")));//据name值分组统计
            List list = c.list();
            for(Object ob : list) {
                Object[] ob1 = (Object[]) ob;
                System.out.println(ob1[1] + " | " + ob1[0]);
            }

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Projections.groupProperty("name")));//name去重后列表
            List<String> list = c.list();
            for(String s : list) {
                System.out.println(s);
            }

用alias()方法为指定投影指定别名

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Projections.alias(Projections.count("name"), "count"))//指定别名
                    .add(Projections.groupProperty("name")))
                    .addOrder(Order.desc("count"));//用别名排序
            List list = c.list();
            for(Object ob : list) {
                Object[] ob1 = (Object[]) ob;
                System.out.println(ob1[1] + " | " + ob1[0]);
            }

 b、选择查询（指定要查找的列）

查询一列

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Property.forName("name")));
            List<String> list = c.list();
            for(String s : list) {
                System.out.println(s);
            }

查询多列

　　　　     Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .createAlias("criteriaTeacher", "ct")
                    .setProjection(Projections.projectionList()
                    .add(Property.forName("ct.name"))
                    .add(Property.forName("name")));
            List list = c.list();
            for(Object ob : list) {
                Object[] ob1 = (Object[]) ob;
                System.out.println(ob1[1] + " | " + ob1[0]);
            }

5、离线查询和子查询

DetachedCriteria代表离线查询（允许再session范围之外创建一个查询）和子查询（把DetachedCriteria的查询结果传入Criteria中作为查询条件时，DetachedCriteria就变成了子查询）

　　　　　　  DetachedCriteria sub = DetachedCriteria
                    .forClass(CriteriaTeacher.class)
                    .setProjection(Projections.projectionList()
                    .add(Property.forName("id")))
                    .add(Restrictions.like("name", "%1%"));

            Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .add(Subqueries.propertyIn("criteriaTeacher", sub));
            List<CriteriaStudent> list = c.list();
            for(CriteriaStudent s : list) {
                System.out.println(s.getName() + " | " + s.getCriteriaTeacher().getName());
            }

 

下面是测试学习时用到的持久化类

@Entity
@Table(name = "criteria_teacher")
public class CriteriaTeacher {
    @Id
    @GeneratedValue
    private Long id;
    private String name;
    @OneToMany(targetEntity = CriteriaStudent.class, mappedBy = "criteriaTeacher")
    private Set<CriteriaStudent> criteriaStudents = new HashSet<CriteriaStudent>();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<CriteriaStudent> getCriteriaStudents() {
        return criteriaStudents;
    }

    public void setCriteriaStudents(Set<CriteriaStudent> criteriaStudents) {
        this.criteriaStudents = criteriaStudents;
    }
}

@Entity
@Table(name = "criteria_student")
public class CriteriaStudent {
    @Id
    @GeneratedValue
    private Long id;
    private String name;
    @ManyToOne(targetEntity = CriteriaTeacher.class)
    @JoinColumn(name = "teacher_id", referencedColumnName = "id", nullable = false)
    private CriteriaTeacher criteriaTeacher;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public CriteriaTeacher getCriteriaTeacher() {
        return criteriaTeacher;
    }

    public void setCriteriaTeacher(CriteriaTeacher criteriaTeacher) {
        this.criteriaTeacher = criteriaTeacher;
    }
}

测试类

public class CriteriaTestController {
    public static void main(String[] args) {
        Configuration cf = new Configuration().configure();
        SessionFactory sf = cf.buildSessionFactory();
        Session session = sf.openSession();
        Transaction ts = session.beginTransaction();
        try {
            Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Property.forName("name")));
            List<String> list = c.list();
            for(String s : list) {
                System.out.println(s);
            }
            ts.commit();
        } finally {
            session.close();
            sf.close();
        }
    }
}