JPA標準WHERE子句

WHERE子句用於對資料庫應用條件並基於該條件獲取資料。 在Criteria API中，AbstractQuery介面的where()方法用於設定查詢條件。

標準WHERE範例

在這裡，我們將在student表上執行多個WHERE操作。假設該表包含以下記錄 -

DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `S_ID` int(11) NOT NULL,
  `S_NAME` varchar(255) DEFAULT NULL,
  `S_AGE` int(11) DEFAULT NULL,
  PRIMARY KEY (`S_ID`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('101', 'Gaurav', '24');
INSERT INTO `student` VALUES ('102', 'Rahul', '22');
INSERT INTO `student` VALUES ('103', 'Chris', '20');
INSERT INTO `student` VALUES ('104', 'Ronit', '26');
INSERT INTO `student` VALUES ('105', 'Roy', '21');

現在，請按照以下步驟執行操作: -

第1步: 建立一個實體類。在com.yiibai.jpa包下建立了StudentEntity.java類檔案。 該類包含三個屬性:s_id，s_name，s_age以及所有必需的註解。

檔案:StudentEntity.java -

package com.yiibai.jpa;

import javax.persistence.*;

@Entity
@Table(name = "student")
public class StudentEntity {

    @Id
    private 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;
    }

}

第2步: 將實體類和其他資料庫組態對映到 persistence.xml 檔案中。

檔案:Persistence.xml -

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
    xmlns="http://xmlns.jcp.org/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="Student_details">
        <class>com.yiibai.jpa.StudentEntity</class>  
        <properties>
            <property name="javax.persistence.jdbc.driver"
                value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url"
                value="jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC" />
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password"
                value="123456" />
            <property name="eclipselink.logging.level" value="SEVERE" />
            <property name="eclipselink.ddl-generation"
                value="create-or-extend-tables" />
        </properties>
    </persistence-unit>

</persistence>

這裡，我們建立了基本實體類並將組態對映到persistence.xml 檔案中，可以通過以下方式執行不同型別的SELECT排序操作 -

1. JPQL大於和小於條件

在這裡，我們將通過一個簡單的範例演示如何從資料庫指定大於和小於條件查詢獲取符合條件的資料。

檔案:Comparison.java -

package com.yiibai.jpa.jpql;

import com.yiibai.jpa.StudentEntity;
import javax.persistence.*;
import javax.persistence.criteria.*;

import java.util.*;

public class Comparison {

    public static void main(String args[]) {

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");
        EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();

        CriteriaBuilder cb = em.getCriteriaBuilder();

        AbstractQuery<StudentEntity> cq1 = cb.createQuery(StudentEntity.class);
        AbstractQuery<StudentEntity> cq2 = cb.createQuery(StudentEntity.class);

        Root<StudentEntity> stud1 = cq1.from(StudentEntity.class);

        cq1.where(cb.greaterThan(stud1.get("s_age"), 22));

        CriteriaQuery<StudentEntity> select1 = ((CriteriaQuery<StudentEntity>) cq1).select(stud1);
        TypedQuery<StudentEntity> tq1 = em.createQuery(select1);
        List<StudentEntity> list1 = tq1.getResultList();

        System.out.println("Students having age greater than 22");

        System.out.print("s_id");
        System.out.print("\t s_name");
        System.out.println("\t s_age");

        for (StudentEntity s : list1) {
            System.out.print(s.getS_id());
            System.out.print("\t" + s.getS_name());
            System.out.println("\t" + s.getS_age());
        }

        Root<StudentEntity> stud2 = cq2.from(StudentEntity.class);

        cq2.where(cb.lessThan(stud2.get("s_age"), 22));

        CriteriaQuery<StudentEntity> select2 = ((CriteriaQuery<StudentEntity>) cq2).select(stud2);
        TypedQuery<StudentEntity> tq2 = em.createQuery(select2);
        List<StudentEntity> list2 = tq2.getResultList();

        System.out.println("Students having age Less than 22");

        System.out.print("s_id");
        System.out.print("\t s_name");
        System.out.println("\t s_age");

        for (StudentEntity s : list2) {
            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();
    }
}

執行上面程式碼，得到以下輸出結果 -

Students having age greater than 22
s_id     s_name     s_age
101    Gaurav    24
104    Ronit    26
Students having age Less than 22
s_id     s_name     s_age
103    Chris    20
105    Roy    21

2. JPQL Between條件

在這裡，我們將通過一個簡單的範例演示如何從資料庫指定Between條件查詢獲取符合條件的資料。

檔案:Between.java -

package com.yiibai.jpa.jpql;

import com.yiibai.jpa.StudentEntity;
import javax.persistence.*;
import javax.persistence.criteria.*;

import java.util.*;

public class Between {

    public static void main(String args[]) {

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");
        EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();

        CriteriaBuilder cb = em.getCriteriaBuilder();

        AbstractQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

        Root<StudentEntity> stud = cq.from(StudentEntity.class);

        cq.where(cb.between(stud.get("s_age"), 22, 26));
        CriteriaQuery<StudentEntity> select = ((CriteriaQuery<StudentEntity>) cq).select(stud);
        TypedQuery<StudentEntity> tq = em.createQuery(select);
        List<StudentEntity> list = tq.getResultList();

        System.out.println("Students having age between 22 and 26");

        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();
    }
}

執行上面程式碼，得到以下輸出結果 -

Students having age between 22 and 26
s_id     s_name     s_age
101    Gaurav    24
102    Rahul    22
104    Ronit    26

3. JPQL Like條件

在這裡，我們將通過一個簡單的範例演示如何從資料庫指定Like條件查詢獲取符合條件的資料。

檔案:Like.java -

package com.yiibai.jpa.jpql;

import com.yiibai.jpa.StudentEntity;
import javax.persistence.*;
import javax.persistence.criteria.*;

import java.util.*;

public class Like {

    public static void main(String args[]) {

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");
        EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();

        CriteriaBuilder cb = em.getCriteriaBuilder();

        AbstractQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

        Root<StudentEntity> stud = cq.from(StudentEntity.class);

        cq.where(cb.like(stud.get("s_name"), "R%"));
        CriteriaQuery<StudentEntity> select = ((CriteriaQuery<StudentEntity>) cq).select(stud);
        TypedQuery<StudentEntity> tq = em.createQuery(select);
        List<StudentEntity> list = tq.getResultList();

        System.out.println("Students name starting with R");

        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();
    }
}

執行上面範例程式碼，得到以下結果 -

Students name starting with R
s_id     s_name     s_age
102    Rahul    22
104    Ronit    26
105    Roy    21

4. JPQL In條件

在這裡，我們將通過一個簡單的範例演示如何從資料庫指定In條件查詢獲取符合條件的資料。

檔案:Like.java -

package com.yiibai.jpa.jpql;

import com.yiibai.jpa.StudentEntity;
import javax.persistence.*;
import javax.persistence.criteria.*;

import java.util.*;

public class In {

    public static void main(String args[]) {

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");
        EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();

        CriteriaBuilder cb = em.getCriteriaBuilder();

        AbstractQuery<StudentEntity> cq = cb.createQuery(StudentEntity.class);

        Root<StudentEntity> stud = cq.from(StudentEntity.class);

        cq.where(cb.in(stud.get("s_age")).value(22).value(24));
        CriteriaQuery<StudentEntity> select = ((CriteriaQuery<StudentEntity>) cq).select(stud);
        TypedQuery<StudentEntity> tq = em.createQuery(select);
        List<StudentEntity> list = tq.getResultList();

        System.out.println("Students having age 22 and 24");

        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();
    }
}

執行上面範例程式碼，得到以下結果 -

Students having age 22 and 24
s_id     s_name     s_age
101    Gaurav    24
102    Rahul    22