hibernate之條件查詢

一、條件查詢簡介

條件查詢是更據面向對象特色的數據查詢方式，主要通過如下3個類完成

1、Criteria：代表一次查詢

2、Criterion：代表一個查詢條件

3、Restrictions：產生查詢條件的工具類

執行條件查詢的步驟

1、獲取Hibernate session對象

2、調用session的createCriteria()方法創建Criteria查詢對象

3、使用Restrictions的靜態方法創建Criterion查詢條件

4、通過Criteria的add()方法添加查詢條件到Criteria查詢中

5、執行Criteria的list()或uniqueResult()方法返回結果集

二、條件查詢

1、整表查詢

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

2、加入查詢條件（通過Criteria的add()方法和Restrictions的靜態方法添加）

　　　　　　  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、關聯查詢（前提持久化類內部有映射關系）

 如果需要使用關聯實體的屬性來增加查詢條件，則需再次使用createCriteria()方法

a、默認鏈接方式

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .add(Restrictions.like("name", "%1%"))
                    .createCriteria("criteriaTeacher")
　　　　　　　　　　　　//.createCriteria("criteriaTeacher", "ct")//為關聯實體指定別名
                    .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、指定鏈接方式

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .add(Restrictions.like("name", "%1%"))
                    .createCriteria("criteriaTeacher", JoinType.LEFT_OUTER_JOIN);//左連接方式
            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、分組查詢

hibernate中使用Projection接口代表投影運算，hibernate通過Criteria的setProjection(Projections p)方法進行投影運算，其中Projections作為產生Projection的工廠。

a、投影運算查詢

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Projections.rowCount()));//統計表中記錄條數
            System.out.println(c.uniqueResult());

　　　　　　  Criteria c = session
                    .createCriteria(CriteriaStudent.class)
                    .setProjection(Projections.projectionList()
                    .add(Projections.count("name"))
                    .add(Projections.groupProperty("name")));//據name值分組統計
            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()方法為指定投影指定別名

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

 b、選擇查詢（指定要查找的列）

查詢一列

　　　　　　  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);
            }

查詢多列

　　　　     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、離線查詢和子查詢

DetachedCriteria代表離線查詢（允許再session范圍之外創建一個查詢）和子查詢（把DetachedCriteria的查詢結果傳入Criteria中作為查詢條件時，DetachedCriteria就變成了子查詢）

　　　　　　  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());
            }

 

下面是測試學習時用到的持久化類

@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;
    }
}

測試類

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();
        }
    }
}

 代碼下載：https://github.com/shaoyesun/hibernate_study.git