springjpa（二）动态多条件分页查询

实际开发中，查询这一操作是必不可少的。根据多个条件动态查询的需求是普通的不能再普通的需求了。所以这篇介绍一种根据条件动态查询的方法。顺便介绍下分页。

在上一篇中，StudentRepository接口继承了JpaRepository。这种适用于简单的增删改查。

现在让StudentRepository再继承一个JpaSpecificationExecutor，这样子就方便我们多种条件的查询了。

先看下JpaSpecificationExecutor接口的方法

public interface JpaSpecificationExecutor<T> {
    T findOne(Specification<T> var1);

    List<T> findAll(Specification<T> var1);

    Page<T> findAll(Specification<T> var1, Pageable var2);

    List<T> findAll(Specification<T> var1, Sort var2);

    long count(Specification<T> var1);
}

所有的条件都拼装成了Specification条件类。

现在StudentRepository的接口是这样的

public interface StudentRepository extends JpaRepository<Student, Long>, JpaSpecificationExecutor<Student> {

    List<Student> findByNameLike(String name);

    List<Student> findByAgeGreaterThanAndNameEquals(Integer age, String name);
}

较原来多继承了一个JpaSpecificationExecutor，下面我们模仿有name值时就根据name模糊查询，有age值时就查询等于这个age的值，此处增加两个类StudentService和StudentServiceImpl

package com.vincent.service;

import com.vincent.model.Student;

import java.util.List;

/**
 * @author 
 * @date 2018/8/21 下午4:27
 */
public interface StudentService {

    List<Student> getStudents(String name, Integer age);
}

　　

package com.vincent.service.impl;

import com.vincent.demo.dao.StudentRepository;
import com.vincent.demo.entity.Student;
import com.vincent.demo.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import java.util.ArrayList;
import java.util.List;

/**
 * @author rw
 * @date 2019/1/14 下午10:10
 */
@Service
public class StudentServiceImpl implements StudentService {
    @Autowired
    StudentRepository studentRepository;

    @Override
    public List<Student> getStudents(String name, Integer age) {
        return studentRepository.findAll((Root<Student> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) -> {
            List<Predicate> list = new ArrayList<>();
            if (name != null) {
                list.add(criteriaBuilder.equal(root.get("name"), name));
            }
            if (age != null) {
                list.add(criteriaBuilder.equal(root.get("age"), age));
            }
            Predicate[] p = new Predicate[list.size()];
            return criteriaBuilder.and(list.toArray(p));
        });
    }
}

　　测试

    @Test
    public void testSelect2() {
        System.out.println(studentService.getStudents(null, 12));
        System.out.println(studentService.getStudents("a", 12));
    }

　　

分页

接口

Page<Student> getStudents(String name, Integer age, Pageable pageable);

 实现

@Override
    public Page<Student> getStudents(String name, Integer age, Pageable pageable) {
        return studentRepository.findAll((Root<Student> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) -> {
            Predicate predicate = null;
            if (name != null) {
                predicate = criteriaBuilder.equal(root.get("name"), name);
            }
            if (age != null) {
                predicate = criteriaBuilder.equal(root.get("age"), age);
            }
            return predicate;
        }, pageable);
    }

　测试

 @Test
    public void testSelect3() {
        Page<Student> students = studentService.getStudents(null, null, new PageRequest(0, 2));
        System.out.println(students.getContent());
        System.out.println(students.getTotalPages());
    }

　结果

2018-09-05 13:50:15.308 INFO 3953 --- [ main] o.h.h.i.QueryTranslatorFactoryInitiator : HHH000397: Using ASTQueryTranslatorFactory
[Student{id=111, name='cba', age=121, schoolId=1}, Student{id=1111, name='vincent', age=22, schoolId=1}]
7

这里有个小注意点，new PageRequest(0, 2)这边的分页pageNum是从0开始的，同时pageNum不可以为负数！