springboot+mybatisplus 入门自学（单表+多表）

1. 新建一个spring boot项目

2. 参考https://baomidou.com/pages/779a6e/ 可以自己实现自动生成

也可以按照如下来完成
先引入pom

`
org.springframework.boot
spring-boot-starter

    
        org.springframework.boot
        spring-boot-starter-test
        test
    
    
    
        com.baomidou
        mybatis-plus-generator
        3.5.3
    

    
    
        io.springfox
        springfox-boot-starter
        3.0.0
    

    
        org.projectlombok
        lombok
    

    
        com.baomidou
        mybatis-plus-boot-starter
        3.5.2
    

    
        mysql
        mysql-connector-java
    

    
        org.freemarker
        freemarker
    
    

    
    
        org.springframework.boot
        spring-boot-starter-web
    `
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修改配置文件：

spring:
  datasource:
    url: jdbc:mysql:///java_shop
    username: root
    password:
    driver-class-name: com.mysql.cj.jdbc.Driver
  mvc:
    pathmatch:
      matching-strategy: ant_path_matcher
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增加一个测试类：

public class Test {

    public static void main(String[] args) {
        FastAutoGenerator.create("jdbc:mysql:///java_shop", "root", "")
                .globalConfig(builder -> {
                    builder.author("zt") // 设置作者
                            .enableSwagger() // 开启 swagger 模式
                            .fileOverride() // 覆盖已生成文件
                            .outputDir("D:\\Program Files\\idea_workspace\\202207\\mp\\src\\main\\java"); // 指定输出目录
                })
                .packageConfig(builder -> {
                    builder.parent("com.zt") // 设置父包名
                            //.moduleName("system") // 设置父包模块名
                            .pathInfo(Collections.singletonMap(OutputFile.xml, "D:\\Program Files\\idea_workspace\\202207\\mp\\src\\main\\resources\\mappers")); // 设置mapperXml生成路径
                })
                .strategyConfig(builder -> {
                    builder.addInclude("java_user") // 设置需要生成的表名
                            .addTablePrefix("java_"); // 设置过滤表前缀
                })
                .strategyConfig(builder -> {
                    builder.addInclude("java_cart") // 设置需要生成的表名
                            .addTablePrefix("java_"); // 设置过滤表前缀
                })
                .templateEngine(new FreemarkerTemplateEngine()) // 使用Freemarker引擎模板，默认的是Velocity引擎模板
                .execute();

    }
}
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修改连接数据库的url 、username、password, 包名，还有就是你要生成的表名

运行如上代码后，就会自动生成相应的controller、service、mapper、entity等

以上红框内的内容都是自动生成的，以上代码可以实现简单的单表增删改查操作：
例如在mapper层：
查询所有：selectList
增加： insert
根据id删除：deleteById
根据id修改： updateById
根据id查询：selectById
这里可以参考https://baomidou.com/pages/49cc81/#service-crud-接口

 注意点： **以上程序若想执行成功，需要在启动类头上配置@MapperScan("com.zt.mapper")**
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测试一下以上的生成：

1. 在启动类增加@MapperScan(“com.zt.mapper”)
2. 新增一个测试方法
   
   测试结果如下，表示成功：
   

3. mp多表联查

1.引入依赖

        <dependency>
            <groupId>com.github.yulichanggroupId>
            <artifactId>mybatis-plus-joinartifactId>
            <version>1.2.4version>
        dependency>
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2.一对多
一个商品对应一种类型

@TableName("java_categroy")
@Data
@ToString
@ApiModel(value = "Categroy对象", description = "")
public class Categroy implements Serializable {

    private static final long serialVersionUID = 1L;

    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;

    private String name;

    @ApiModelProperty("1.一级   2.二级  3.三级")
    private Integer type;

    @ApiModelProperty("父级id，若是一级，则是0 ")
    private Integer parentId;

    @ApiModelProperty("显示时的顺序")
    private Integer orderNum;

    private LocalDateTime createTime;

    private LocalDateTime updateTime;
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@Data
@ToString
@TableName("java_product")
@ApiModel(value = "Product对象", description = "")
public class Product implements Serializable {

    private static final long serialVersionUID = 1L;

    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;

    private String pname;

    private String image;

    @ApiModelProperty("产品详情")
    private String detail;

    @ApiModelProperty("分类id")
    private Integer categroyId;

    private Object price;

    @ApiModelProperty("库存")
    private Integer stock;

    private LocalDateTime createTime;

    private LocalDateTime updateTime;
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产生中间实体：修改相同字段

@Data
public class ProductDto extends Categroy implements Serializable {

    private static final long serialVersionUID = 1L;

    private Integer pid;

    private String pname;

    private String image;

    @ApiModelProperty("产品详情")
    private String detail;

    @ApiModelProperty("分类id")
    private Integer categroyId;

    private Object price;

    @ApiModelProperty("库存")
    private Integer stock;

    private LocalDateTime pcreateTime;

    private LocalDateTime pupdateTime;
   @Override
    public String toString() {
        return "Product{" +
            "pid = " + pid +
            ", pname = " + pname +
            ", image = " + image +
            ", detail = " + detail +
            ", categroyId = " + categroyId +
            ", price = " + price +
            ", stock = " + stock +
            ", pcreateTime = " + pcreateTime +
            ", pupdateTime = " + pupdateTime +
             ",   Categroy{ id = " + super.getId() +
                    ", name = " + getName() +
        "}";
    }
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修改mapper的extends MPJBaseMapper

public interface ProductMapper extends MPJBaseMapper<Product> {

}
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修改service接口

public interface IProductService extends IService<Product> {

    List<ProductDto> selectAllProduct();
}
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修改service实现

@Service
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> implements IProductService {

    @Autowired
    private  ProductMapper productMapper;
    @Override
    public List<ProductDto> selectAllProduct() {
        List<ProductDto> list = productMapper.selectJoinList(ProductDto.class,
                new MPJLambdaWrapper<Product>()
                .selectAll(Product.class)
                .selectAll(Categroy.class)
                .selectAs(Product::getId,ProductDto::getPid)
                .selectAs(Product::getCreateTime,ProductDto::getPcreateTime)
                .selectAs(Product::getUpdateTime,ProductDto::getPupdateTime)
                .leftJoin(Categroy.class,Categroy::getId,Product::getCategroyId)
                .ne(Product::getStock,0)
        );
        return list;
    }
}


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编写测试类

 @Autowired
    private IProductService productService;
    @Test
    public void test02(){
        List<ProductDto> list = productService.selectAllProduct();
        list.forEach(System.out::println);
    }
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测试结果：

多对多操作：

@Override
    public List<OrderDto> selectByUid(Integer uid, Integer flag) {
        List<OrderDto> list ;
        if (flag == null){
            list = orderMapper.selectJoinList(OrderDto.class,
                    new MPJLambdaWrapper<Order>()
                            .selectAll(Order.class)
                            .selectAs(Order::getId,OrderDto::getDid)
                            .selectAs(Order::getCreateTime,OrderDto::getDcreateTime)
                            .selectAs(Order::getUpdateTime,OrderDto::getDupdateTime)
                            .eq(Order::getUserId,uid)
            );
        }else{
            list = orderMapper.selectJoinList(OrderDto.class,
                    new MPJLambdaWrapper<Order>()
                            .selectAll(Order.class)
                            .selectAs(Order::getId,OrderDto::getDid)
                            .selectAs(Order::getCreateTime,OrderDto::getDcreateTime)
                            .selectAs(Order::getUpdateTime,OrderDto::getDupdateTime)
                            .eq(Order::getUserId,uid)
                            .eq(Order::getOrderStatus,flag)
            );
        }

        if(list.size()>0){
          for (OrderDto item : list){
              LambdaQueryWrapper<OderItem> wrapper = Wrappers.lambdaQuery(OderItem.class)
                                                             .in(OderItem::getOrderNo, item.getOrderNo());
              // 通过订单号查询顶顶那详情
              List<OderItem> listoderitem = oderItemMapper.selectList(wrapper);
              List<OderItemDto> itemDtos = new ArrayList<>();
              if (listoderitem.size()>0){
                   for(int i = 0 ; i < listoderitem.size(); i++){
                       OderItemDto dto = new OderItemDto();
                       LambdaQueryWrapper<Product> wrapper1 = Wrappers.lambdaQuery(Product.class)
                               .eq(Product::getId, listoderitem.get(i).getProductId());
                       Product product =  productService.getOne(wrapper1);
                       dto.setPname(product.getPname());
                       dto.setQuantity(listoderitem.get(i).getQuantity());
                       dto.setUnitPrice(listoderitem.get(i).getUnitPrice());
                       itemDtos.add(dto);
                   }
                  }
                  item.setList(itemDtos);
              }
        }       
        return list;
    }
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可以去资源下载项目参考： smp_shop