hibernate中查询方式(二):常用查询

Collection(集合)

列出所有有学生参加的项目:(项目的学生的数量大于0,则表示有学生参加)

public void testCollection() throws Exception {
        Session session = HibernateUtil.getInstance().getSession();
        //使用size属性或者SIZE函数来计算一个集合的元素数量放在where条件中是没有区别的
        // 都是一个子查询完成
        //String hql = "SELECT proj FROM Project proj WHERE proj.students.size > 0";
        String hql = "SELECT proj FROM Project proj WHERE SIZE(proj.students) > 0";
        Query query = session.createQuery(hql);
        List<Project> list = query.list();
        for (Project object : list) {
            System.out.println(object);
        }
        session.close();
    }

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public void testCollection1() throws Exception {
        Session session = HibernateUtil.getInstance().getSession();
        // 判断集合是不是空
        // IS NOT EMPTY: 不是空，
        // IS EMPTY：是空，
　　　　　String hql = "SELECT proj FROM Project proj WHERE proj.students IS NOT EMPTY";
        Query query = session.createQuery(hql);
        @SuppressWarnings("unchecked")
        List<Project> list = query.list();
        for (Project object : list) {
            System.out.println(object);
        }
        session.close();
    }

列出每个班级中学生的平均龄和最小年龄:(AVG(age),MIN(age))

①:先把学生按班级分组把学生的年龄查出来

select  AVG(stu.age),MIN(stu.age) from Student stu group by stu.clazz;

public void testFunction() throws Exception {
        Session session = HibernateUtil.getInstance().getSession();
        String hql = "SELECT stu.id, AVG(stu.age), MIN(stu.age) FROM Student stu GROUP BY stu.clazz";
        Query query = session.createQuery(hql);
        @SuppressWarnings("unchecked")
        List<Object[]> list = query.list();
        for (Object[] object : list) {
            System.out.println(Arrays.toString(object));
        }
        session.close();
    }
}

join(多表联合查询):

列出所有学生的名字对应的班级的名字:

select stu.name,clz.name From Student stu,Clazz clz Where stu.clz=clz  (当学生的班级等于班级的时候)

①:隐式连接

public void Jointest() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT stu.name,clz.name FROM Student stu,Clazz clz WHERE stu.clz=clz";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<Object[]> list = createQuery.list();
        for (Object[] objects : list) {
            System.out.println(Arrays.toString(objects));
        }
    }

②:显示连接 join

select stu.name,clz.name From Student stu  join  Clazz clz on stu.clz=clz  (当学生的班级等于班级的时候)     不能这么写

HQL语句按照上面那么写会报错:org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: on near line 1, column 68 [select stu.name,clz.name From daomian.Student stu  join  Clazz clz on stu.clz=clz]

SELECT stu.name,clz.name FROM Student stu JOIN stu.clz clz

public void Jointest1() {
        Session session = BuildSesssionFactory.getSession();
        //通过Student 对象中Clazz 连接,Student中的外键找Clazz中的主键
        String sql = "SELECT stu.name,clz.name FROM Student stu JOIN stu.clz clz";
        Query createQuery = session.createQuery(sql);
        List<Object[]> list = createQuery.list();
        for (Object[] objects : list) {
            System.out.println(Arrays.toString(objects));
        }
}

limit(分页):

select stu  from Student stu LIMIT 0,2;         不能这么写 HQL中不支持LIMIT关键字

HQL语句按照上面那么写会报错org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: LIMIT near line 1, column 38 [select stu  from daomian.Student stu LIMIT 0,2]

public void testLimit() throws Exception {
        Integer pageNo = 2;
        Integer pageSize = 10;
        // HQL中不支持LIMIT关键字
        Session session = HibernateUtil.getInstance().getSession();
        String hql = "SELECT stu FROM Student stu";
        Query query = session.createQuery(hql);
        // firstResult: 从数据库中的第几条数据开始查询
        query.setFirstResult((pageNo - 1) * pageSize);
        // maxResults: 表示本次分页的最大条数
        query.setMaxResults(pageSize);
        List<Student> list = query.list();
        for (Student object : list) {
            System.out.println(object);
        }
        session.close();
    }

Namedquery:

        // NamedQuery:主要是为了一些经常使用,但是又不愿意每次都写时用
        // 在类的映射文件中添加一个标签,在class标签外添加一个query
        // 在属性name中来指定这个NamedQuery指定属性,
        // 在XML的innerTest中编写HQL语句

public void namedQuerytest() {
        Session session = BuildSesssionFactory.getSession();
        Query namedQuery = session.getNamedQuery("QUERY_ALL_STUDENT");
        @SuppressWarnings("unchecked")
        List<Student> list = namedQuery.list();
        for (Student student : list) {
            System.out.println(student);
        }
        // NamedQuery:主要是为了一些经常使用,但是又不愿意每次都写时用
        // 在类的映射文件中添加一个标签,在class标签外添加一个query
        // 在属性name中来指定这个NamedQuery指定属性,
        // 在XML的innerTest中编写HQL语句
    }

    <query name="QUERY_ALL_STUDENT">SELECT stu FROM Student stu</query>
　　//在Student对象对应的xml中配置
　　这里的query标签中的name属性和java代码中session.getNamedQuery中的值是一样的

paramenter:(查询参数设置)

①:位置占位符

public class ParamenterTest {
    // 查询参数设置:
    // 1、位置占位符:就是使用`?`号来代表查询参数,
    // 通过setParameter(index,object)来根据?的位置来设置参数的;
    @Test
    public void positionTest() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "select stu from Student stu Where stu.age between ? and ?";
        Query createQuery = session.createQuery(sql);
        createQuery.setParameter(0, 18);
        createQuery.setParameter(1, 20);
        @SuppressWarnings("unchecked")
        List<Student> list = createQuery.list();
        for (Student student : list) {
            System.out.println(student);
        }
        session.close();
    }

②:名称占位符

// 2、名称占位符:就是使用`:paramName`号来代表查询参数,
    // 通过setParamter(String name,object)这个方法为名称给占位符添加参数;
    @Test
    public void nameTest() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "select stu from Student stu Where stu.age between :small and :big";
        Query createQuery = session.createQuery(sql);
        createQuery.setParameter("small", 18);
        createQuery.setParameter("big", 20);
        @SuppressWarnings("unchecked")
        List<Student> list = createQuery.list();
        for (Student student : list) {
            System.out.println(student);
        }
        session.close();
    }

用名称占位符的时候,要注意查询语句里边应该是(: 别名) 

设置值的时候为    createQuery.setParameter("别名",值);

Result:(返回结果)

①:查询学生的总数:

Select COUNT(stu) FROM Student stu;

public class ResultTest {
    @Test
    @SuppressWarnings("unchecked")
    public void ResulTest() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT COUNT(stu.id) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        List<Long> list = createQuery.list();
        for (Long long1 : list) {
            System.out.println(long1);
        }
}

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//当查询结果为单条记录的时候,不需要调用list()方法,只需要调用uniqueResult()方法即可
    @Test
    public void ResulTest1() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT COUNT(stu.id) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        Long long1 = (Long) createQuery.uniqueResult();
        System.out.println(long1);
    }

②:返回一个Object[]:

Select  stu.id,stu.name,stu.age FROM Student stu;

    public void ResulTest2() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT stu.id,stu.name,stu.age FROM Student stu";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<Object[]> list = createQuery.list();
        for (Object[] objects : list) {
            System.out.println(Arrays.toString(objects));
        }
    }

③:返回一个list集合

Select  new LIST(stu.id,stu.name,stu.age) FROM Student stu;

    public void ResulTest3() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT NEW LIST(stu.id,stu.name,stu.age) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<List<Student>> list = createQuery.list();
        for (List<Student> list2 : list) {
            System.out.println(list2);
        }
    }

②:返回一个Map集合

Select  new MAP(stu.id,stu.name,stu.age) FROM Student stu;

    public void ResulTest4() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT NEW MAP(stu.id ,stu.name,stu.age) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<Map<String,Student>> list = createQuery.list();
        for (Map<String, Student> map : list) {
            System.out.println(map);
        }
    }

⑤: new Map  给KEY值起一个别名

Select new MAP(stu.id AS ID,stu.name AS NAME,stu.age AS AGE) FROM Student stu;    AS不能省略

public void ResulTest5() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT NEW MAP(stu.id as ID ,stu.name AS NAME,stu.age AS AGE) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<Map<String,Student>> list = createQuery.list();
        for (Map<String, Student> map : list) {
            System.out.println(map);
        }
    }

⑥: new 一个对象   Class  没有配置写全限定名称         VO对象  ValueObject

SELECT NEW StudentVO类的全限定名称(id,name,age) FROM Student stu

public class StudentVO {
    private Long id;
    private String name;
    private Integer age;
//此处省略getter/setter方法
}

public void ResulTest6() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT NEW hibernate.query.result.StudentVO(id,name,age) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<StudentVO> list = createQuery.list();
        for (StudentVO student : list) {
            System.out.println(student);
        }
    }

7:  new一个对象    在映射文件中配置Class(在FROM的那个对象的映射文件中配置)

SELECT NEW StudentVO(id,name,age) FROM Student stu

<import class="hibernate.query.result.StudentVO" rename="StudentVO"/>
//在class标签外   在hibernate-mapping标签内写

public class StudentVO {
    private Long id;
    private String name;
    private Integer age;
//此处省略getter/setter方法
}

    public void ResulTest7() {
        Session session = BuildSesssionFactory.getSession();
        String sql = "SELECT NEW StudentVO(id,name,age) FROM Student stu";
        Query createQuery = session.createQuery(sql);
        @SuppressWarnings("unchecked")
        List<StudentVO> list = createQuery.list();
        for (StudentVO student : list) {
            System.out.println(student);
        }
    }