Week 1-8: Spring Boot 学习计划完整项目

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

week3/src/main/java/com/learn/service/mp/StudentMpService.java

@@ -0,0 +1,131 @@
+package com.learn.service.mp;
+
+import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
+import com.baomidou.mybatisplus.core.metadata.IPage;
+import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
+import com.learn.entity.Student;
+import com.learn.repository.mp.StudentMapper;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * MyBatis-Plus 版本的学生服务
+ *
+ * 重点对比与 JPA 版本的差异：
+ *   1. 新增：MP 用 insert()，JPA 用 save()
+ *   2. 查询：MP 用 LambdaQueryWrapper 构建条件，JPA 用方法命名或 JPQL
+ *   3. 分页：MP 用 Page + IPage，JPA 用 PageRequest + Page
+ *   4. 更新：MP 用 updateById()，JPA 用 save()
+ *
+ * 关键武器：LambdaQueryWrapper
+ *   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）
+ *   例如：wrapper.eq(Student::getName, "张三")  →  WHERE name = '张三'
+ */
+@Service
+public class StudentMpService {
+
+    private final StudentMapper mapper;
+
+    public StudentMpService(StudentMapper mapper) {
+        this.mapper = mapper;
+    }
+
+    // ==================== 增删改查 ====================
+
+    @Transactional
+    public Student add(Student student) {
+        mapper.insert(student);  // MP: insert() 只用于新增
+        return student;          // insert 后 student.id 已被自动回填
+    }
+
+    @Transactional(readOnly = true)
+    public List<Student> list() {
+        // MP 条件构造器：空的 wrapper → 查全部
+        // orderByDesc 让结果按成绩降序
+        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
+        wrapper.orderByDesc(Student::getScore);
+        return mapper.selectList(wrapper);
+    }
+
+    @Transactional(readOnly = true)
+    public Optional<Student> getById(Long id) {
+        return Optional.ofNullable(mapper.selectById(id));
+    }
+
+    @Transactional
+    public Optional<Student> update(Long id, Student updated) {
+        Student existing = mapper.selectById(id);
+        if (existing == null) {
+            return Optional.empty();
+        }
+        if (updated.getName() != null) existing.setName(updated.getName());
+        if (updated.getAge() > 0) existing.setAge(updated.getAge());
+        if (updated.getEmail() != null) existing.setEmail(updated.getEmail());
+        if (updated.getScore() >= 0) existing.setScore(updated.getScore());
+
+        mapper.updateById(existing);  // MP 用 updateById
+        return Optional.of(existing);
+    }
+
+    @Transactional
+    public boolean delete(Long id) {
+        return mapper.deleteById(id) > 0;
+    }
+
+    // ==================== 搜索 ====================
+
+    @Transactional(readOnly = true)
+    public List<Student> searchByKeyword(String keyword) {
+        return mapper.searchByKeyword(keyword);
+    }
+
+    @Transactional(readOnly = true)
+    public List<Student> findByName(String name) {
+        // MP 的 Lambda 方式构建条件
+        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
+        wrapper.like(Student::getName, name);   // WHERE name LIKE '%name%'
+        return mapper.selectList(wrapper);
+    }
+
+    // ==================== 分页（第 5 天） ====================
+
+    @Transactional(readOnly = true)
+    public IPage<Student> page(int pageNum, int pageSize) {
+        // MP 分页：Page<Student>(页码, 每页条数)
+        Page<Student> page = new Page<>(pageNum, pageSize);
+
+        // 按成绩降序
+        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
+        wrapper.orderByDesc(Student::getScore);
+
+        return mapper.selectPage(page, wrapper);
+    }
+
+    // ==================== 统计 ====================
+
+    @Transactional(readOnly = true)
+    public long count() {
+        return mapper.selectCount(null);  // null = 无筛选条件
+    }
+
+    @Transactional(readOnly = true)
+    public long countByScoreRange(int min, int max) {
+        // MP 的 Lambda 方式构建范围条件
+        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
+        wrapper.between(Student::getScore, min, max);  // WHERE score BETWEEN min AND max
+        return mapper.selectCount(wrapper);
+    }
+
+    // ==================== 高级查询（演示 LambdaQueryWrapper 的威力） ====================
+
+    @Transactional(readOnly = true)
+    public List<Student> findExcellentStudents(int threshold) {
+        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
+        wrapper.ge(Student::getScore, threshold)     // WHERE score >= ?
+               .orderByDesc(Student::getScore);
+        return mapper.selectList(wrapper);
+    }
+}