前言

記錄下Mybatis-Plus中條件構造器Wrapper 的一些基本用法。

查詢示例

• 表結構

CREATE TABLE `product` (

  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,

  `title` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,

  `create_time` datetime DEFAULT CURRENT_TIMESTAMP,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB AUTO_INCREMENT=35 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

CREATE TABLE `product_item` (

  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,

  `title` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,

  `product_id` int(10) unsigned NOT NULL,

  `create_time` datetime DEFAULT CURRENT_TIMESTAMP,

  PRIMARY KEY (`id`)

) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

• 實現需求：根據product - id查詢product例項及其關聯的product_item，如下:

基礎程式碼

• ProductController.java

@GetMapping("/{id}")

public ProductWithItemsVo getWithItems(@PathVariable Integer id) {

   return productService.getWithItems(id);

}

• ProductService.java

public interface ProductService {

    ProductWithItemsVo getWithItems(Integer id);

}

• ProductServiceImpl.java

@Service

public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> implements ProductService {

	@Autowired

    private ProductItemMapper productItemMapper;

	@Override

    public ProductWithItemsVo getWithItems(Integer id) {

    	// 實現程式碼

    }

}

• mapper

@Repository

public interface ProductMapper extends BaseMapper<Product> {

}

@Repository

public interface ProductItemMapper extends BaseMapper<ProductItem> {

}

• model

@Getter

@Setter

@TableName("product")

public class Product {

    private Integer id;

    private String title;

    @JsonIgnore

    private Date createTime;

}

@Getter

@Setter

@TableName("product_item")

public class ProductItem {

    private Integer id;

    private Integer productId;

    private String title;

    @JsonIgnore

    private Date createTime;

}

• vo出參

@Data

@NoArgsConstructor

public class ProductWithItemsVo {

    private Integer id;

    private String title;

    List<ProductItem> items;

	/**

     * 構造ProductWithItemsVo物件用於出參

     * @param product

     * @param items

     */

    public ProductWithItemsVo(Product product, List<ProductItem> items) {

        BeanUtils.copyProperties(product, this);

        this.setItems(items);

    }

}

QueryWrapper 的基本使用

@Override

public ProductWithItemsVo getWithItems(Integer id) {

    Product product = this.getById(id);

    if (Objects.isNull(product)) {

        System.out.println("未查詢到product");

        return null;

    }

    /**

     * wrapper.eq("banner_id", id)

     * banner_id 資料庫欄位

     * id 判斷相等的值

     */

    QueryWrapper<ProductItem> wrapper = new QueryWrapper<>();

    wrapper.eq("product_id", id);

    List<ProductItem> productItems = productItemMapper.selectList(wrapper);

    return new ProductWithItemsVo(product, productItems);

}

• 如上程式碼，通過條件構造器QueryWrapper查詢出當前product例項及其關聯的product_item

QueryWrapper 的lambada寫法

@Override

    public ProductWithItemsVo getWithItems(Integer id) {

        Product product = this.getById(id);

        if (Objects.isNull(product)) {

            System.out.println("未查詢到product");

            return null;

        }

        QueryWrapper<ProductItem> wrapper = new QueryWrapper<>();

        /**

         * lambda方法引用

         */

        wrapper.lambda().eq(ProductItem::getProductId, id);

        List<ProductItem> productItems = productItemMapper.selectList(wrapper);

        return new ProductWithItemsVo(product, productItems);

    }

• 如上程式碼，通過條件構造器QueryWrapper的lambda方法引用查詢出當前product例項及其關聯的product_item

LambadaQueryWrapper 的使用

• LambadaQueryWrapper 用於Lambda語法使用的QueryWrapper
• 構建LambadaQueryWrapper 的方式：

 /**

   * 方式一

   */

  LambdaQueryWrapper<ProductItem> wrapper1 = new QueryWrapper<ProductItem>().lambda();

  wrapper1.eq(ProductItem::getProductId, id);

  List<ProductItem> productItems1 = productItemMapper.selectList(wrapper1);

  /**

   * 方式二

   */

  LambdaQueryWrapper<ProductItem> wrapper2 = new LambdaQueryWrapper<>();

  wrapper2.eq(ProductItem::getProductId, id);

  List<ProductItem> productItems2 = productItemMapper.selectList(wrapper2);

• 完整程式碼

@Override

public ProductWithItemsVo getWithItems(Integer id) {

    Product product = this.getById(id);

    if (Objects.isNull(product)) {

        System.out.println("未查詢到product");

        return null;

    }

    LambdaQueryWrapper<ProductItem> wrapper = new LambdaQueryWrapper<>();

    wrapper.eq(ProductItem::getProductId, id);

    List<ProductItem> productItems = productItemMapper.selectList(wrapper);

    return new ProductWithItemsVo(product, productItems);

}

• 如上程式碼，通過條件構造器LambdaQueryWrapper查詢出當前product例項及其關聯的product_item

LambdaQueryChainWrapper 的鏈式呼叫

@Override

    public ProductWithItemsVo getWithItems(Integer id) {

        Product product = this.getById(id);

        if (Objects.isNull(product)) {

            System.out.println("未查詢到product");

            return null;

        }

        /**

         * 鏈式呼叫

         */

        List<ProductItem> productItems =

                new LambdaQueryChainWrapper<>(productItemMapper)

                        .eq(ProductItem::getProductId, id)

                        .list();

        return new ProductWithItemsVo(product, productItems);

    }

• 如上程式碼，通過鏈式呼叫查詢出當前product例項及其關聯的product_item

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