实战案例

让我们通过一个具体的实战案例来展示项目需求分析、数据库设计以及业务逻辑实现的具体代码实操步骤。我们将创建一个简单的博客系统，包括文章的增删改查功能。

### 1. 项目需求分析

项目需求如下：
- 用户可以查看文章列表。
- 用户可以创建新文章。
- 用户可以编辑和删除已有文章。

### 2. 数据库设计

首先，我们需要设计数据库表。以下是文章表（`posts`）的SQL创建语句：

```sql
CREATE TABLE posts (
  id INT AUTO_INCREMENT PRIMARY KEY,
  title VARCHAR(255) NOT NULL,
  content TEXT NOT NULL,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);
```

### 3. 业务逻辑实现

#### 3.1 设置Spring Boot项目

使用Spring Initializr（https://start.spring.io/）生成一个Spring Boot项目，包含以下依赖：
- Spring Web
- MyBatis Framework
- MySQL Driver

#### 3.2 配置application.properties

在`src/main/resources/application.properties`文件中配置数据库连接：

```properties
spring.datasource.url=jdbc:mysql://localhost:3306/blog?useSSL=false
spring.datasource.username=root
spring.datasource.password=password
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

mybatis.mapper-locations=classpath:mapper/*.xml
```

#### 3.3 创建实体类

在`src/main/java/com/example/blog/model`目录下创建`Post.java`：

```java
package com.example.blog.model;

import java.time.LocalDateTime;

public class Post {
    private Integer id;
    private String title;
    private String content;
    private LocalDateTime createdAt;
    private LocalDateTime updatedAt;

// Getters and setters
}
```

#### 3.4 创建Mapper接口和XML文件

在`src/main/java/com/example/blog/mapper`目录下创建`PostMapper.java`：

```java
package com.example.blog.mapper;

import com.example.blog.model.Post;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;

@Mapper
public interface PostMapper {
    int insertPost(Post post);

int updatePost(Post post);

int deletePost(int id);

@Select("SELECT * FROM posts WHERE id = #{id}")
    Post selectPostById(int id);

@Select("SELECT * FROM posts")
    java.util.List<Post> selectAllPosts();
}
```

在`src/main/resources/mapper`目录下创建`PostMapper.xml`：

```xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.blog.mapper.PostMapper">

<insert id="insertPost" parameterType="com.example.blog.model.Post">
        INSERT INTO posts (title, content) VALUES (#{title}, #{content})
    </insert>

<update id="updatePost" parameterType="com.example.blog.model.Post">
        UPDATE posts SET title = #{title}, content = #{content} WHERE id = #{id}
    </update>

<delete id="deletePost" parameterType="int">
        DELETE FROM posts WHERE id = #{id}
    </delete>

<select id="selectPostById" resultMap="PostResult">
        SELECT * FROM posts WHERE id = #{id}
    </select>

<select id="selectAllPosts" resultMap="PostResult">
        SELECT * FROM posts
    </select>
</mapper>
```

#### 3.5 创建Service层

在`src/main/java/com/example/blog/service`目录下创建`PostService.java`：

```java
package com.example.blog.service;

import com.example.blog.mapper.PostMapper;
import com.example.blog.model.Post;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
public class PostService {
    @Autowired
    private PostMapper postMapper;

public int insertPost(Post post) {
        return postMapper.insertPost(post);
    }

public int updatePost(Post post) {
        return postMapper.updatePost(post);
    }

public int deletePost(int id) {
        return postMapper.deletePost(id);
    }

public Post selectPostById(int id) {
        return postMapper.selectPostById(id);
    }

public List<Post> selectAllPosts() {
        return postMapper.selectAllPosts();
    }
}
```

#### 3.6 创建Controller层

在`src/main/java/com/example/blog/controller`目录下创建`PostController.java`：

```java
package com.example.blog.controller;

import com.example.blog.model.Post;
import com.example.blog.service.PostService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api/posts")
public class PostController {
    @Autowired
    private PostService postService;

@PostMapping
    public int createPost(@RequestBody Post post) {
        return postService.insertPost(post);
    }

@PutMapping("/{id}")
    public int updatePost(@PathVariable int id, @RequestBody Post post) {
        post.setId(id);
        return postService.updatePost(post);
    }

@DeleteMapping("/{id}")
    public int deletePost(@PathVariable int id) {
        return postService.deletePost(id);
    }

@GetMapping("/{id}")
    public Post getPostById(@PathVariable int id) {
        return postService.selectPostById(id);
    }

@GetMapping
    public List<Post> getAllPosts() {
        return postService.selectAllPosts();
    }
}
```

以上步骤展示了从项目需求分析到数据库设计，再到业务逻辑实现的具体代码实操。这个简单的博客系统包含了文章的增删改查功能，涵盖了Spring Boot和MyBatis的基本使用。