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JPA Criteria API

Criteria API was introduced in JPA 2.0. Using this API we can define queries dynamically via construction of an object-based javax.persistence.CriteriaQuery instance rather than string-based approach used in JPQL (Java Persistence Query Language).

Constructing a CriteriaQuery

Step 1: Create CriteriaBuilder object by invoking getCriteriaBuilder() method of EntityManager.

CriteriaBuilder cb = em.getCriteriaBuilder();

Step 2: Create an instance of CriteriaQuery interface to create a query object.

CriteriaQuery<Student> criteriaQuery = cb.createQuery(Student.class);

Step 3: Specify query roots by invoking from() method of CriteriaQuery. Query roots specify the domain objects on which the query is evaluated.

Root<Student> from = criteriaQuery.from(Student.class);

Step 4: Call the select method of CriteriaQuery Object to specify type of query result.

criteriaQuery.select(from);

Step 6:  Create the Predicate by calling the restriction methods of CriteriaBuilder. Here we are putting a restriction to select sname which is equal to Manu Manjunatha.

Predicate predicate = cb.equal(from.get("sname"), "Manu Manjunatha");

Step 7: Apply the Predicate by invoking where method of CriteriaQuery.

criteriaQuery.where(predicate);

JPA Criteria Example

Database script (MySQL)

CREATE        TABLE ADDRESS(

AID INT(5) PRIMARY KEY AUTO_INCREMENT,

CITY VARCHAR(30),

ZIPCODE VARCHAR(30)

);                

 

CREATE TABLE STUDENT(

SID INT(5) PRIMARY KEY AUTO_INCREMENT,

SNAME VARCHAR(30),

AID INT(5),

CONSTRAINT FOREIGN KEY (AID) REFERENCES ADDRESS (AID)

);

 

INSERT  INTO ADDRESS(AID,CITY,ZIPCODE) VALUES (1,'Bangalore', '560010');

 

INSERT  INTO STUDENT(SID,SNAME,AID) VALUES (1,'Manu Manjunatha', 1);

INSERT  INTO STUDENT(SID,SNAME,AID) VALUES (2,'Advith Tyagraj', 1);

INSERT  INTO STUDENT(SID,SNAME,AID) VALUES (3,'Likitha', 1);

INSERT  INTO STUDENT(SID,SNAME,AID) VALUES (4,'Tyagraj', 1);

 

pom.xml

<project xmlns="https://maven.apache.org/POM/4.0.0" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"

        xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/maven-v4_0_0.xsd">

        <modelVersion>4.0.0</modelVersion>

        <groupId>com.java4coding</groupId>

        <artifactId>JPA_Criteria</artifactId>

        <packaging>jar</packaging>

        <version>1.0-SNAPSHOT</version>

        <name>JPA_Criteria</name>

        <url>https://maven.apache.org</url>

        <dependencies>

                <dependency>

                        <groupId>junit</groupId>

                        <artifactId>junit</artifactId>

                        <version>3.8.1</version>

                        <scope>test</scope>

                </dependency>

                <dependency>

                        <groupId>org.eclipse.persistence</groupId>

                        <artifactId>javax.persistence</artifactId>

                        <version>2.0.0</version>

                </dependency>

 

                <dependency>

                        <groupId>org.hibernate</groupId>

                        <artifactId>hibernate-entitymanager</artifactId>

                        <version>4.2.8.Final</version>

                </dependency>

 

                <dependency>

                        <groupId>mysql</groupId>

                        <artifactId>mysql-connector-java</artifactId>

                        <version>8.0.11</version>

                </dependency>

        </dependencies>

</project>

 

persistence.xml

<?xml version="1.0" encoding="UTF-8"?>

<persistence xmlns="https://java.sun.com/xml/ns/persistence"

        xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"

        xsi:schemaLocation="https://java.sun.com/xml/ns/persistence

             https://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"

        version="2.0">

 

        <persistence-unit name="StudentPU">

                <provider>org.hibernate.ejb.HibernatePersistence</provider>

                <properties>

                        <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/study" />

                        <property name="hibernate.connection.driver_class" value="com.mysql.cj.jdbc.Driver" />

                        <property name="hibernate.connection.username" value="root" />

                        <property name="hibernate.connection.password" value="root" />

                        <property name="hibernate.archive.autodetection" value="class" />

                        <property name="hibernate.show_sql" value="true" />

                        <property name="hibernate.format_sql" value="true" />

                        <property name="hbm2ddl.auto" value="update" />

                </properties>

        </persistence-unit>

</persistence>

Address.java

package com.java4coding;

 

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

 

@Entity

@Table(name = "ADDRESS")

public class Address {

       

        @Id

        private int aid;

       

        private String city;

 

        private String zipcode;

 

        public int getAid() {

                return aid;

        }

        public void setAid(int aid) {

                this.aid = aid;

        }

        public String getCity() {

                return city;

        }

        public void setCity(String city) {

                this.city = city;

        }

        public String getZipcode() {

                return zipcode;

        }

        public void setZipcode(String zipcode) {

                this.zipcode = zipcode;

        }

}

Student.java

package com.java4coding;

 

import javax.persistence.CascadeType;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

 

@Entity

@Table(name = "STUDENT")

public class Student {

       

        @Id

        @GeneratedValue(strategy = GenerationType.AUTO)

        private int sid;

       

        private String sname;

       

        @ManyToOne(cascade = CascadeType.ALL)

        @JoinColumn(name= "AID")

        private Address address;

 

        public int getSid() {

                return sid;

        }

        public void setSid(int sid) {

                this.sid = sid;

        }

        public String getSname() {

                return sname;

        }

        public void setSname(String sname) {

                this.sname = sname;

        }

        public Address getAddress() {

                return address;

        }

        public void setAddress(Address address) {

                this.address = address;

        }

}

Test.java

package com.java4coding;

 

import java.util.List;

 

import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;

import javax.persistence.criteria.CriteriaBuilder;

import javax.persistence.criteria.CriteriaQuery;

import javax.persistence.criteria.Predicate;

import javax.persistence.criteria.Root;

 

public class Test {

        public static void main(String[] args) {

                EntityManagerFactory emf = Persistence.createEntityManagerFactory("StudentPU");

                EntityManager em = emf.createEntityManager();

                em.getTransaction().begin();

               

                //Create CriteriaBuilder object by invoking getCriteriaBuilder() method of EntityManager.

                CriteriaBuilder cb = em.getCriteriaBuilder();

               

                //Create an instance of CriteriaQuery interface to create a query object.

                CriteriaQuery<Student> criteriaQuery = cb.createQuery(Student.class);

               

                //Specify query roots by invoking from() method of CriteriaQuery

                //query roots specify the domain objects on which the query is evaluated.

                Root<Student> from = criteriaQuery.from(Student.class);

               

                //Call the select method of CriteriaQuery Object to specify type of query result.

                criteriaQuery.select(from);

               

                //Create the Predicate by calling the restriction methods of CriteriaBuilder.

                //Here we are putting a restriction to select sname which is equal to Manu Manjunatha

                Predicate predicate = cb.equal(from.get("sname"), "Manu Manjunatha");

               

                //Apply the Predicate by invoking where method of CriteriaQuery

                criteriaQuery.where(predicate);

 

                List<Student> results = em.createQuery(criteriaQuery).getResultList();

               

                for(Student s: results) {

                        System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" );

                        if (s.getSname() != null) {

                                System.out.println("Student name: " + s.getSname());

                        }

                        if (s.getSid() != 0) {

                                System.out.println("Student ID: " + s.getSid());

                        }

                        if (s.getAddress().getCity() != null) {

                                System.out.println("Student City: " + s.getAddress().getCity());

                        }

                        if (s.getAddress().getCity() != null) {

                                System.out.println("Student City: " + s.getAddress().getCity());

                        }

                        if (s.getAddress().getZipcode() != null) {

                                System.out.println("Student Zipcode: " + s.getAddress().getZipcode());

                        }

                        System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" );

                }

               

                em.getTransaction().commit();

        }

}

Project directory structure

jpa-criteria-0
 

Output:

Hibernate:

    select

        student0_.sid as sid1_1_,

        student0_.AID as AID3_1_,

        student0_.sname as sname2_1_

    from

        STUDENT student0_

    where

        student0_.sname=?

Hibernate:

    select

        address0_.aid as aid1_0_0_,

        address0_.city as city2_0_0_,

        address0_.zipcode as zipcode3_0_0_

    from

        ADDRESS address0_

    where

        address0_.aid=?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Student name: Manu Manjunatha

Student ID: 1

Student City: Bangalore

Student City: Bangalore

Student Zipcode: 560010

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

 

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