MapStruct中枚举字段的映射忽略策略：处理集合与单个对象的正确姿势

@Entity
public class Document {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String type; // 源对象中的类型是String
    // ... 其他字段
}

@Data
public class DocumentDTO {
    private Integer id;
    private DocumentsEnum type; // 目标对象中的类型是Enum
    // ... 其他字段
}

public enum DocumentsEnum {
    MAIN, SECONDARY, OTHER
}

@Mapper(componentModel = "spring") // 或其他组件模型
public interface DocumentsMapper {

    // 尝试在此处忽略type字段，但通常无效
    @Mapping(source = "type", target = "type", ignore = true)
    List<DocumentDTO> mapper(List<Document> documentList);

    @AfterMapping
    default void afterMapping(Document document, @MappingTarget DocumentDTO documentDTO) {
        // 期望在此处手动处理documentDTO.setType()
        // 但如果上面的@Mapping不生效，type可能已经被自动映射
    }
}

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.MappingTarget;
import org.mapstruct.AfterMapping;

import java.util.List;

@Mapper(componentModel = "spring") // 或其他组件模型
public interface DocumentsMapper {

    // 1. 集合映射方法：MapStruct会智能地使用下面的单对象映射方法
    List<DocumentDTO> listMapper(List<Document> documentList);

    // 2. 单对象映射方法：在此处应用@Mapping(ignore = true)
    @Mapping(source = "type", target = "type", ignore = true) // 忽略type字段的自动映射
    DocumentDTO documentToDocumentDTO(Document document);

    // 3. 后置处理逻辑：在自动映射（排除已忽略字段）完成后执行
    @AfterMapping
    default void afterMapping(Document document, @MappingTarget DocumentDTO documentDTO) {
        // 在这里可以根据document.getType()的值，自定义设置documentDTO.setType()
        // 例如：
        if ("MAIN_DOC".equals(document.getType())) {
            documentDTO.setType(DocumentsEnum.MAIN);
        } else if ("SECONDARY_DOC".equals(document.getType())) {
            documentDTO.setType(DocumentsEnum.SECONDARY);
        } else {
            documentDTO.setType(DocumentsEnum.OTHER);
        }
    }
}

// --- Entity ---
// 假设这是JPA实体或其他数据源对象
public class Document {
    private Integer id;
    private String type; // 源类型为String

    // Getters and Setters
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }
    public String getType() { return type; }
    public void setType(String type) { this.type = type; }

    // Constructor for easy testing
    public Document(Integer id, String type) {
        this.id = id;
        this.type = type;
    }
}

// --- DTO ---
public class DocumentDTO {
    private Integer id;
    private DocumentsEnum type; // 目标类型为Enum

    // Getters and Setters
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }
    public DocumentsEnum getType() { return type; }
    public void setType(DocumentsEnum type) { this.type = type; }

    @Override
    public String toString() {
        return "DocumentDTO{" +
               "id=" + id +
               ", type=" + type +
               '}';
    }
}

// --- Enum ---
public enum DocumentsEnum {
    MAIN, SECONDARY, OTHER
}

// --- Mapper Interface ---
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.MappingTarget;
import org.mapstruct.AfterMapping;
import org.mapstruct.factory.Mappers;

import java.util.List;

@Mapper // MapStruct会自动生成实现类
public interface DocumentsMapper {

    // 获取Mapper实例（如果未使用Spring等组件模型）
    DocumentsMapper INSTANCE = Mappers.getMapper(DocumentsMapper.class);

    // 1. 集合映射方法
    List<DocumentDTO> listMapper(List<Document> documentList);

    // 2. 单对象映射方法，并在此处忽略type字段的自动映射
    @Mapping(source = "type", target = "type", ignore = true)
    DocumentDTO documentToDocumentDTO(Document document);

    // 3. 后置处理逻辑，用于自定义type字段的映射
    @AfterMapping
    default void afterMapping(Document document, @MappingTarget DocumentDTO documentDTO) {
        // 根据源Document的type字符串值，自定义设置DTO的DocumentsEnum
        if ("MAIN_DOCUMENT".equals(document.getType())) {
            documentDTO.setType(DocumentsEnum.MAIN);
        } else if ("SECONDARY_DOCUMENT".equals(document.getType())) {
            documentDTO.setType(DocumentsEnum.SECONDARY);
        } else {
            // 对于不匹配的类型，可以设置为OTHER或抛出异常
            documentDTO.setType(DocumentsEnum.OTHER);
        }
    }
}

// --- Usage Example ---
public class MainApplication {
    public static void main(String[] args) {
        List<Document> documents = List.of(
            new Document(1, "MAIN_DOCUMENT"),
            new Document(2, "SECONDARY_DOCUMENT"),
            new Document(3, "UNKNOWN_DOCUMENT")
        );

        DocumentsMapper mapper = DocumentsMapper.INSTANCE;
        List<DocumentDTO> dtos = mapper.listMapper(documents);

        dtos.forEach(System.out::println);
        // 预期输出:
        // DocumentDTO{id=1, type=MAIN}
        // DocumentDTO{id=2, type=SECONDARY}
        // DocumentDTO{id=3, type=OTHER}
    }
}