132 lines
4.6 KiB
Java
132 lines
4.6 KiB
Java
package com.learn.service.mp;
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import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
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import com.baomidou.mybatisplus.core.metadata.IPage;
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import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
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import com.learn.entity.Student;
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import com.learn.repository.mp.StudentMapper;
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import org.springframework.stereotype.Service;
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import org.springframework.transaction.annotation.Transactional;
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import java.util.List;
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import java.util.Optional;
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/**
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* MyBatis-Plus 版本的学生服务
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*
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* 重点对比与 JPA 版本的差异：
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* 1. 新增：MP 用 insert()，JPA 用 save()
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* 2. 查询：MP 用 LambdaQueryWrapper 构建条件，JPA 用方法命名或 JPQL
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* 3. 分页：MP 用 Page + IPage，JPA 用 PageRequest + Page
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* 4. 更新：MP 用 updateById()，JPA 用 save()
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*
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* 关键武器：LambdaQueryWrapper
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* 用它构建条件，不用担心列名写错（基于 Lambda 表达式，编译期安全）
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* 例如：wrapper.eq(Student::getName, "张三") → WHERE name = '张三'
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*/
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@Service
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public class StudentMpService {
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private final StudentMapper mapper;
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public StudentMpService(StudentMapper mapper) {
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this.mapper = mapper;
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}
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// ==================== 增删改查 ====================
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@Transactional
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public Student add(Student student) {
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mapper.insert(student); // MP: insert() 只用于新增
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return student; // insert 后 student.id 已被自动回填
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}
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@Transactional(readOnly = true)
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public List<Student> list() {
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// MP 条件构造器：空的 wrapper → 查全部
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// orderByDesc 让结果按成绩降序
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LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
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wrapper.orderByDesc(Student::getScore);
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return mapper.selectList(wrapper);
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}
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@Transactional(readOnly = true)
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public Optional<Student> getById(Long id) {
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return Optional.ofNullable(mapper.selectById(id));
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}
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@Transactional
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public Optional<Student> update(Long id, Student updated) {
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Student existing = mapper.selectById(id);
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if (existing == null) {
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return Optional.empty();
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}
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if (updated.getName() != null) existing.setName(updated.getName());
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if (updated.getAge() > 0) existing.setAge(updated.getAge());
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if (updated.getEmail() != null) existing.setEmail(updated.getEmail());
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if (updated.getScore() >= 0) existing.setScore(updated.getScore());
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mapper.updateById(existing); // MP 用 updateById
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return Optional.of(existing);
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}
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@Transactional
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public boolean delete(Long id) {
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return mapper.deleteById(id) > 0;
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}
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// ==================== 搜索 ====================
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@Transactional(readOnly = true)
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public List<Student> searchByKeyword(String keyword) {
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return mapper.searchByKeyword(keyword);
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}
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@Transactional(readOnly = true)
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public List<Student> findByName(String name) {
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// MP 的 Lambda 方式构建条件
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LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
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wrapper.like(Student::getName, name); // WHERE name LIKE '%name%'
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return mapper.selectList(wrapper);
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}
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// ==================== 分页（第 5 天） ====================
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@Transactional(readOnly = true)
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public IPage<Student> page(int pageNum, int pageSize) {
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// MP 分页：Page<Student>(页码, 每页条数)
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Page<Student> page = new Page<>(pageNum, pageSize);
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// 按成绩降序
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LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
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wrapper.orderByDesc(Student::getScore);
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return mapper.selectPage(page, wrapper);
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}
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// ==================== 统计 ====================
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@Transactional(readOnly = true)
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public long count() {
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return mapper.selectCount(null); // null = 无筛选条件
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}
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@Transactional(readOnly = true)
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public long countByScoreRange(int min, int max) {
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// MP 的 Lambda 方式构建范围条件
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LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
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wrapper.between(Student::getScore, min, max); // WHERE score BETWEEN min AND max
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return mapper.selectCount(wrapper);
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}
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// ==================== 高级查询（演示 LambdaQueryWrapper 的威力） ====================
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@Transactional(readOnly = true)
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public List<Student> findExcellentStudents(int threshold) {
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LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
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wrapper.ge(Student::getScore, threshold) // WHERE score >= ?
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.orderByDesc(Student::getScore);
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return mapper.selectList(wrapper);
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}
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}
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