Spring JPA - create specification that returns entities in random order (MySql ORDER BY RAND() function)

// CriteriaQuery<?> query = ...

// CriteriaBuilder builder = ...

​

// put inside toPredicate function following line:

//

query.orderBy(builder.asc(builder.function("RAND", null))); // MySql RAND() function used

​

// do not use sort parameter using PageRequest:

//

PageRequest pageRequest = PageRequest.of(pageNumber - 1, pageSize);

package com.example.controllers;

​

import org.springframework.data.domain.Page;

import org.springframework.data.domain.PageRequest;

import org.springframework.http.MediaType;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.bind.annotation.ResponseBody;

​

import javax.servlet.http.HttpServletRequest;

​

import com.example.utils.HttpUtils;

import com.example.database.repositories.OffersRepository; // use your repository here

import com.example.database.specifications.OffersSpecification;

import com.example.database.entities.OfferEntity;

​

@Controller

public class OffersController {

​

    @Autowired

    private OffersRepository offersRepository,

​

    @RequestMapping(

            method = RequestMethod.GET,

            value = "/offers",

            produces = MediaType.APPLICATION_JSON_VALUE

    )

    @ResponseBody

    public List<OfferEntity> getOffers(HttpServletRequest request) {

​

        int pageNumber = 1;

        int pageSize = 20;

​

        OffersSpecification offersSpecification = new OffersSpecification();

        PageRequest pageRequest = PageRequest.of(pageNumber - 1, pageSize); // do not add here sort parameter here

​

        Page<OfferEntity> pagedOffers = this.offersRepository.findAll(offersSpecification, pageRequest);

​

        return pagedOffers;

    }

}

package com.example.database.specifications;

​

import org.springframework.data.jpa.domain.Specification;

​

import javax.persistence.criteria.CriteriaBuilder;

import javax.persistence.criteria.CriteriaQuery;

import javax.persistence.criteria.Predicate;

import javax.persistence.criteria.Root;

​

import com.example.database.entities.OfferEntity;

​

public class OffersSpecification implements Specification<OfferEntity> {

​

    @Override

    public Predicate toPredicate(Root<OfferEntity> root, CriteriaQuery<?> query, CriteriaBuilder builder) {

        Predicate predicate = builder.and();

​

        // ...

​

        query.orderBy(builder.asc(builder.function("RAND", null))); // MySql RAND() function used

​

        return predicate;

    }

}

package com.example.database.entities;

​

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.Entity;

import javax.persistence.Table;

​

import java.util.Date;

​

@Entity

@Table(name = "offers")

public class OfferEntity

{

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    private Long id;

​

    // other fields ...    

​

    private Long parentId;

    private Date publicationTime;

​

    // getters and setters ...

}