ORDER BY子句用于对数据排序并以升序或降序排列它们。 CriteriaQuery接口提供了orderBy()方法来定义排序类型。
举例订购
在这里, 我们将对学生表执行几个ORDER BY操作。让我们假设该表包含以下记录：-
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现在, 请按照以下步骤执行操作：-
- 创建一个实体类。在这里, 我们在com.srcmini.jpa包下创建了StudentEntity.java。此类包含三个属性s_id, s_name, s_age和所有必需的注释。
package com.srcmini.jpa;
import javax.persistence.*;
@Entity @Table(name="student") public class StudentEntity {@Idprivate int s_id;
private String s_name;
private int s_age;
public StudentEntity(int s_id, String s_name, int s_age) {super();
this.s_id = s_id;
this.s_name = s_name;
this.s_age = s_age;
}public StudentEntity() {super();
}public int getS_id() {return s_id;
}public void setS_id(int s_id) {this.s_id = s_id;
}public String getS_name() {return s_name;
}public void setS_name(String s_name) {this.s_name = s_name;
}public int getS_age() {return s_age;
}public void setS_age(int s_age) {this.s_age = s_age;
} }- 现在, 在Persistence.xml文件中映射实体类和其他数据库配置。
<
persistence>
<
persistence-unit name="Student_details">
<
class>
com.srcmini.jpa.StudentEntity<
/class>
<
properties>
<
property name="javax.persistence.jdbc.driver" value="http://www.srcmini.com/com.mysql.jdbc.Driver"/>
<
property name="javax.persistence.jdbc.url" value="http://www.srcmini.com/jdbc:mysql://localhost:3306/studentdata"/>
<
property name="javax.persistence.jdbc.user" value="http://www.srcmini.com/root"/>
<
property name="javax.persistence.jdbc.password" value=""/>
<
property name="eclipselink.logging.level" value="http://www.srcmini.com/SEVERE"/>
<
property name="eclipselink.ddl-generation" value="http://www.srcmini.com/create-or-extend-tables"/>
<
/properties>
<
/persistence-unit>
<
/persistence>
- 一旦创建了基本实体类, 并将配置映射到persistence.xml文件中, 就可以通过以下方式执行不同类型的选择操作：-
Asc.java
package com.srcmini.jpa.jpql;
import com.srcmini.jpa.StudentEntity;
import javax.persistence.*;
import javax.persistence.criteria.*;
import java.util.*;
public class Asc { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" );
EntityManager em = emf.createEntityManager();
em.getTransaction().begin( );
CriteriaBuilder cb=em.getCriteriaBuilder();
CriteriaQuery<
StudentEntity>
cq=cb.createQuery(StudentEntity.class);
Root<
StudentEntity>
stud=cq.from(StudentEntity.class);
cq.orderBy(cb.asc(stud.get("s_age")));
CriteriaQuery<
StudentEntity>
select = cq.select(stud);
TypedQuery<
StudentEntity>
q = em.createQuery(select);
List<
StudentEntity>
list = q.getResultList();
System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");
for(StudentEntity s:list){System.out.print(s.getS_id());
System.out.print("\t"+s.getS_name());
System.out.println("\t"+s.getS_age());
} em.getTransaction().commit();
em.close();
emf.close();
}}输出：
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降序排列
Desc.java
package com.srcmini.jpa.jpql;
import com.srcmini.jpa.StudentEntity;
import javax.persistence.*;
import javax.persistence.criteria.*;
import java.util.*;
public class Desc { public static void main( String args[]) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" );
EntityManager em = emf.createEntityManager();
em.getTransaction().begin( );
CriteriaBuilder cb=em.getCriteriaBuilder();
CriteriaQuery<
StudentEntity>
cq=cb.createQuery(StudentEntity.class);
Root<
StudentEntity>
stud=cq.from(StudentEntity.class);
cq.orderBy(cb.desc(stud.get("s_age")));
CriteriaQuery<
StudentEntity>
select = cq.select(stud);
TypedQuery<
StudentEntity>
q = em.createQuery(select);
List<
StudentEntity>
list = q.getResultList();
System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");
for(StudentEntity s:list){System.out.print(s.getS_id());
System.out.print("\t"+s.getS_name());
System.out.println("\t"+s.getS_age());
} em.getTransaction().commit();
em.close();
emf.close();
}}【JPA ORDER BY子句】输出：
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