Spring Data JPA Repository 方法回傳null處理

Spring Data JPA Repository方法回傳結果為空時，可以回傳null物件或以Optional包裝回傳。

注意在Spring Data JPA 2.0後才支援回傳Java 8的Optional。

例如entity類Employee的Repository EmployeeRepository繼承JpaRepository的回傳結果可以是Employee或Optional<Employee>。

EmployeeRepository

package com.abc.demo.repository;

import com.abc.demo.entity.Employee;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;

import java.util.Optional;

@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long> {

    Employee findByName(String name); // 回傳Employee，若查詢結果為空則內容為null

    @Query("select e from Employee e where e.name = :name")
    Optional<Employee> findByNameJPQL(@Param("name") String name); // 回傳Optional包裝的Employee

}

EMPLOYEE現有ㄧ資料如下。

INSERT INTO EMPLOYEE (ID, NAME, AGE) VALUES (1, 'John', 22);

測試程式。

EmployeeRepositoryTests

package com.abc.demo.repository;

import com.abc.demo.entity.Employee;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.Optional;

@SpringBootTest
class EmployeeRepositoryTests {

    @Autowired
    private EmployeeRepository employeeRepository;

    @Test
    void findByName_returnNull() {
        Employee employee = employeeRepository.findByName("Jack");
        System.out.println(employee); // null

        Assertions.assertNull(employee);
    }

    @Test
    void findByName_returnOptionalIsEmpty() {
        Optional<Employee> employeeOptional = employeeRepository.findByNameJPQL("Jack");
        System.out.println(employeeOptional.isPresent()); // false

        Assertions.assertFalse(employeeOptional.isPresent());
    }

}

參考github。

• Null Handling of Repository Methods
• Spring Boot 2 + Spring Data JPA + MySQL 8 簡單範例
• Spring Data JPA Query Method 方法名稱查詢範例