映射struct如何初始化字段

Question

我有一个类似的DTO

@Data
public class MessageDTO implements Serializable {
private Long id;
}

和一个实体

@Entity
@Data
public class Message implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private Long id;
@Column(name = "timestamp")
private Instant timestamp;
}

我想创建一个映射器来将DTO映射到实体。如何使字段private Instant timestamp;具有Instant.now((这样的值？

到目前为止我的映射器

@Mapper(componentModel = "spring", imports = Instant.class)
public interface MessageMapper extends EntityMapper<MessageDTO, Message> {
@Override
@Mapping(target = "timestamp", source = "" ,defaultExpression = "java(Instant.now())")
Message toEntity(MessageDTO dto);
}

它得到了编译错误

Compilation failure
[ERROR] /D:/Shared/projects/IdeaProjects/medical/src/main/java/io/medical/service/mapper/MessageMapper.java:[22,45] No property named "" exists in source parameter(s)

Answer 1

问题是由于source为空。移除source并使用expression而不是defaultExpression。

@Mapper(componentModel = "spring")
public interface MessageMapper extends EntityMapper<MessageDTO, Message> {
@Override
@Mapping(target = "timestamp", expression = "java(Instant.now())")
Message toEntity(MessageDTO dto);
}

如果存在源，但解析时源为null，则defaultExpression可以方便地为目标分配值。