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Spring Data Series (Part 4): @Query Annotation

Check out this hands-on tutorial detailing how to use @Query annotations in Spring Data.

· Java Zone

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Overview

We know that we can delegate query creation to Spring Data. Spring Data is smart enough to derive queries based on the method name. But sometimes, delegation doesn't suit our needs. The way Spring Data creates the query doesn't meet our requirements, so we need to customize the query. Using the @Query annotation, we can customize our query and instruct Spring data to take this customize query, not yours.

When the @Query Annotation Is Needed

  1. Suppose you want to build a query that takes a variety of filtered criteria. Say I want to fetch "Person" based on name, country, gender, and age. We can achieve this via a Spring Data method convention, like findPersonbyNameAndCountryAndGenderAndAge but the readability is pretty bad. So, let's avoid this and use the @Query annotation and create your own query with a suitable method name.

    @Query("select p from Person p where p.name like ?1 and p.country like
    ?2 and gender like ?3 and age=?4  order by country")


    findPerson(String name,String country,String gender,Integer age);

  2. Suppose you want to sort your query by a specific property — for example, the name.

  3. Suppose you want to override the CRUDRepository findOne method. Just redefine this method, maintaining the signature, and put an @Query annotation with your customized query, Now Spring data takes your version. 

    @Query("select p from Person p where p.id = ?1 and  country='America'")

  4. You need to define the functionality not provided by the Repository interface.

Example

Let's take an example where we create a custom method — findByCountryContains  and Override CrudRepository findoneMethod.
package com.example.repo;

import java.util.List;

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.querydsl.QueryDslPredicateExecutor;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

import com.example.person.Person;

@Repository
public interface PersonRepositary extends CrudRepository<Person, Long>,QueryDslPredicateExecutor<Person> {

    @Query("select p from Person p where p.country like ?1 order by country")
    List<Person> findByCountryContains(String country);

    List<Person> findPersonByHobbyName(String name);

    @Query("select p from Person p where p.id = ?1 and  country='America'")
    Person findOne(Long id);           
}

package com.example.person;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Person {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;
    private String name;
    private String country;
    private String gender;

    @OneToMany(mappedBy="person",targetEntity=Hobby.class,
        fetch=FetchType.EAGER,cascade=CascadeType.ALL)
    List<Hobby> hobby;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getCountry() {
        return country;
    }
    public void setCountry(String country) {
        this.country = country;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }           

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }           

    public List<Hobby> getHobby() {
        return hobby;
    }
    public void setHobby(List<Hobby> hobby) {
        this.hobby = hobby;
    }

    public void addHobby(Hobby ihobby)
    {
        if(hobby == null)
        {
            hobby = new ArrayList<Hobby>();
        }
        hobby.add(ihobby);
    }
    @Override
    public String toString() {
        return "Person [id=" + id + ", name=" + name + ", country=" + country + ", gender=" + gender + "]";
    }                    
}

package com.example.person;

import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

import com.example.repo.HobbyRepository;
import com.example.repo.PersonRepositary;
import com.querydsl.core.types.dsl.BooleanExpression;


@SpringBootApplication
@EnableJpaRepositories("com.example.repo")
public class PersonApplication {

    @Autowired
    HobbyRepository hRepo;
    private static final Logger log = LoggerFactory.getLogger(PersonApplication.class);

    @Bean
    public CommandLineRunner demo(PersonRepositary repository) {

        //insertPerson(repository);
        //findPersonByHobbyname(repository,"Photography");
        //findPersonByNameQueryDsl(repository,"Photography");
        //findPersonByCountry(repository,"India");
        Person p = repository.findOne(13L);
        log.info("Person " + p);
        return null;
    }

    private void findPersonByNameQueryDsl(PersonRepositary repository,String hobby)
    {
        BooleanExpression nameExpr = QPerson.person.name.contains("Shamik");

        Iterable<Person> pList = repository.findAll(nameExpr);
        for(Person p : pList)
        log.info("Person " + p);
    }

    private void findPersonByHobbyname(PersonRepositary repository,String hobby)
    {
        List<Person> pList = repository.findPersonByHobbyName(hobby);
        for(Person p : pList)
        log.info("Person " + p);
    }

    private void findPersonByCountry(PersonRepositary repository,String country)
    {
        List<Person> pList = repository.findByCountryContains(country);
        for(Person p : pList)
        log.info("Person " + p);
    }

    private void insertPerson(PersonRepositary repository)
    {                       
        Person p = new Person();
        p.setName("Samir mitra");
        p.setCountry("America");
        p.setGender("male");

        Person p1 = new Person();
        p1.setName("Shamik mitra");
        p1.setCountry("India");
        p1.setGender("male");

        repository.save(p);
        repository.save(p1);

        Hobby hobby1 =new Hobby();
        hobby1.setName("Photography");
        hobby1.setPerson(p);                     

        Hobby hobby2 =new Hobby();
        hobby2.setName("Dancing");
        hobby2.setPerson(p1);

        Hobby hobby3 =new Hobby();
        hobby3.setName("Photography");
        hobby3.setPerson(p1);

        hRepo.save(hobby1);
        hRepo.save(hobby2);
        hRepo.save(hobby3);

    }         
    public static void main(String[] args) {                      
        SpringApplication.run(PersonApplication.class, args);       
    }
}


Output

person0_.country as country2_1_,
person0_.gender as gender3_1_,
person0_.name as name4_1_
and person0_.country='America'
2016-10-07 12:29:39.570  INFO 5744 --- [main] com.example.person.PersonApplication : Person Person [id=13, name=Samir mitra, country=America, gender=male]

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Topics:
spring ,spring data gosling ,java ,jvm

Published at DZone with permission of Shamik Mitra, DZone MVB. See the original article here.

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