MapStruct高级应用：将DTO中的外键ID映射到关联实体对象

@Entity
@Data
@Table(name="products")
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name="name")
    private String name;

    // ... 其他字段 ...

    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "category_id")
    private Category category; // 关联的Category实体

    // ... 其他关联和字段 ...
}

@Data
public class ProductRequestDto {
    private String name;
    // ... 其他字段 ...
    private Long categoryId; // 只包含Category的ID
    // ... 其他字段 ...
}

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.MappingTarget;
import org.springframework.beans.factory.annotation.Autowired;
import java.util.List;
import java.util.Optional;

// 将接口改为抽象类
@Mapper(componentModel = "spring")
public abstract class ProductMapper { 
    // ...
}

// ... (imports)

@Mapper(componentModel = "spring")
public abstract class ProductMapper {

    @Autowired
    protected CategoryRepository categoryRepository; // 注入CategoryRepository

    // ... 映射方法 ...
}

// ... (imports)

@Mapper(componentModel = "spring")
public abstract class ProductMapper {

    @Autowired
    protected CategoryRepository categoryRepository;

    // 自定义方法：将categoryId解析为Category实体
    protected Category resolveCategory(Long categoryId) {
        if (categoryId == null) {
            return null;
        }
        // 使用findById查找Category，并处理Optional
        Optional<Category> categoryOptional = categoryRepository.findById(categoryId);
        return categoryOptional.orElse(null); // 如果未找到，返回null
        // 或者 categoryOptional.orElseThrow(() -> new EntityNotFoundException("Category not found with id: " + categoryId));
    }

    // ... 映射方法 ...
}

// ... (imports)

@Mapper(componentModel = "spring")
public abstract class ProductMapper {

    @Autowired
    protected CategoryRepository categoryRepository;

    protected Category resolveCategory(Long categoryId) {
        if (categoryId == null) {
            return null;
        }
        Optional<Category> categoryOptional = categoryRepository.findById(categoryId);
        return categoryOptional.orElse(null);
    }

    // 映射ProductRequestDto到Product实体
    @Mapping(target = "category", source = "categoryId") // 指定categoryId映射到category
    public abstract Product dtoToProduct(ProductRequestDto productDto);

    // 其他映射方法，例如更新方法
    @Mapping(target = "category", source = "categoryId")
    public abstract void update(@MappingTarget Product product, ProductRequestDto productDto);

    // ... 其他映射方法 ...
}

package com.example.mapper; // 根据您的包名调整

import com.example.dto.ProductRequestDto;
import com.example.dto.ProductResponseDto;
import com.example.entity.Category;
import com.example.entity.Product;
import com.example.repository.CategoryRepository; // 假设您有CategoryRepository

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.MappingTarget;
import org.springframework.beans.factory.annotation.Autowired;

import java.util.List;
import java.util.Optional;

@Mapper(componentModel = "spring")
public abstract class ProductMapper {

    @Autowired
    protected CategoryRepository categoryRepository; // 注入CategoryRepository

    // 自定义方法：将categoryId解析为Category实体
    protected Category resolveCategory(Long categoryId) {
        if (categoryId == null) {
            return null;
        }
        // 使用findById查找Category，并处理Optional
        Optional<Category> categoryOptional = categoryRepository.findById(categoryId);
        // 根据业务需求处理未找到的情况：返回null或抛出异常
        return categoryOptional.orElse(null); 
    }

    // 将ProductRequestDto映射到Product实体
    @Mapping(target = "category", source = "categoryId") // 明确指定categoryId映射到category
    // 如果Product实体中还有其他ManyToOne关联（如discount），也需要类似处理
    // @Mapping(target = "discount", source = "discountId") // 假设ProductRequestDto中有discountId
    public abstract Product dtoToProduct(ProductRequestDto productDto);

    // 将Product实体映射到ProductResponseDto
    // 对于从实体到DTO的映射，MapStruct会自动处理关联对象的ID提取
    @Mapping(target = "categoryId", source = "category.id") // 明确指定category.id映射到categoryId
    public abstract ProductResponseDto productToDto(Product product);

    // 批量映射Product实体到ProductResponseDto列表
    public abstract List<ProductResponseDto> productToDto(List<Product> products);

    // 更新现有Product实体
    @Mapping(target = "id", ignore = true) // 更新时通常忽略ID
    @Mapping(target = "category", source = "categoryId")
    public abstract void update(@MappingTarget Product product, ProductRequestDto productDto);
}