Paging and Sorting
Overview
When we perform bulk operations, like finding all "Person"s from the database or finding everyone based on a country, often we do the paging so that we can present a small data chunk to the end user and, in the next request, we fetch the next data chunk. By doing this, we got two main advantages.Advantages
Enhancing readability for end users if we show whole data on a page then the page will be enough long with Scrollbar, the end user has to scroll for finding a particular person which is a bad UI design.Reduce the Query time and enhance the performance as in spite of fetch all data we only fetch a small chunk of data so less query time. Many UI technology support client side paging which at a time fetch all data and based on use request show paginated data but this is not reducing the query time it only provide the advantage number 1.
Disadvantages:
To request every data chunk One server trip is required. You can optimize it through caching .
2 . When an end user in the process of fetching data another Person added to the system it may possible, the last entry of a page again shown in next page as a first entry.
But we are always using paging to fetch a small chunk of data rather than whole data.
Spring Data and Pagination
Spring data provides support for pagination , It creates all the logic to implement a paging like a count the rows for total pages , create data store specific queries etc.
To implement Paging is very easy in Spring data just we need to follow the below steps,
1. In your custom repository just extends PagingAndSortingRepository
2. Create a PageRequest Object which is an implementation of Pageable interface
This PageRequest Object takes page number, limit of the page (page size) and sorts direction and sort field.
3. By passing requested page number and page limit you can get the data for this page.
If you pass a wrong page number Spring data will take care of that and not return any data.
Paging Code implementation
1. Create a repository which extends PagingAndSortingRepository
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.data.repository.PagingAndSortingRepository;
import org.springframework.stereotype.Repository;
import com.example.person.Person;
public interface PersonRepositary extends PagingAndSortingRepository<Person, Long>,QueryDslPredicateExecutor<Person> {
("select p from Person p where p.country like ?1 order by country")
List<Person> findByCountryContains(String country);
List<Person> findPersonByHobbyName(String name);
("select p from Person p where p.id = ?1 and country='America'")
Person findOne(Long id);
}
2.Create Domain Objects
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;
public class Person {
(strategy=GenerationType.AUTO)
private Long id;
private String name;
private String country;
private String gender;
(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);
}
public String toString() {
return "Person [id=" + id + ", name=" + name + ", country=" + country + ", gender=" + gender + "]";
}
3. Fetch all person, Here I assume per page entry is one so create a PageRequest Object with limit 1 and requesting for the first page.
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.domain.PageRequest;
import org.springframework.data.domain.Sort;
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;
("com.example.repo")
public class PersonApplication {
HobbyRepository hRepo;
private static final Logger log = LoggerFactory.getLogger(PersonApplication.class);
public CommandLineRunner demo(PersonRepositary repository) {
findAll(repository);
return null;
}
private PageRequest gotoPage(int page)
{
PageRequest request = new PageRequest(page,1)
return request;
}
private void findAll(PersonRepositary repository)
{
Iterable<Person> pList = repository.findAll(gotoPage(0));
for(Person p : pList)
log.info("Person " + p);
}
public static void main(String[] args) {
SpringApplication.run(PersonApplication.class, args);
}
}
Output
Hibernate:
select
count(person0_.id) as col_0_0_
from
person person0_
Hibernate:
select
person0_.id as id1_1_,
person0_.country as country2_1_,
person0_.gender as gender3_1_,
person0_.name as name4_1_
from
person person0_ limit ?
Paging and Sorting Code implementation:
To do sorting we have to pass the sort direction and sorting fields along with page number and limit. Suppose we want to sort by country name in ascending order we modify the goto
method like following.
method like following.
private PageRequest gotoPage(int page)
{
PageRequest request = new PageRequest(page,1,Sort.Direction.ASC,"country");
return request;
}
Output:
select
count(person0_.id) as col_0_0_
from
person person0_
Hibernate:
select
person0_.id as id1_1_,
person0_.country as country2_1_,
person0_.gender as gender3_1_,
person0_.name as name4_1_
from
person person0_
order by
Here we pass the ascending order and country property.
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