英文:
Default value to another bean property when Source is null MapStruct
问题
好的，以下是您提供的内容的翻译：
在MapStruct中，我有以下的Mapper：
@Mapping(source = "payload.after", target = "payload")
TargetEntity toTarget(SourceEntity source);
有时候 payload.after 是空的，我需要用另一个属性来填充，叫做 payload.before。类似这样：
@Mapping(source = "payload.after", target = "payload")
// 或者，如果 payload.after 为空
@Mapping(source = "payload.before", target = "payload")
TargetEntity toTarget(SourceEntity source);
我尝试过这样写，但没有生效：
@Mapping(source = "payload.after", target = "payload", defaultValue = "payload.before")
TargetEntity toTarget(SourceEntity source);
有没有办法实现这个需求呢？
英文:
Well, I have the following Mapper in MapStruct:
@Mapping(source = "payload.after", target = "payload")
TargetEntity toTarget(SourceEntity source);
Sometimes payload.after is null and I need to fill with another property, called payload.before. Something like this:
@Mapping(source = "payload.after", target = "payload")
//OR, if payload.after is null
@Mapping(source = "payload.before", target = "payload")
TargetEntity toTarget(SourceEntity source);
I tried used in this way but didn't work:
@Mapping(source = "payload.after", target = "payload", defaultValue = "payload.before")
TargetEntity toTarget(SourceEntity source);
Is there a way to do it?
答案1
得分: 3
从MapStruct文档中我看到，只有您可以使用预定义的值：https://mapstruct.org/documentation/stable/reference/html/#default-values-and-constants
但是您可以通过使用像@AfterMapping或@BeforeMapping这样的注释来轻松实现，详细示例请查看MapStruct文档中的示例 
编辑：
@Mapping(target = "otherTargetField", source = "otherSrcField")
TargetEntity toTarget(SourceEntity source);
@AfterMapping
void toTargetAfterMapping(@MappingTarget TargetEntity, SourceEntity source) {
// 您的映射之后的逻辑，使用 payload.before 和 payload.after
}
MapStruct会自动解析，该方法在映射方法末尾在最后一个返回语句之前被调用。如果想了解更多信息，请参阅MapStruct文档 - 使用 before 和 after 进行自定义映射。
另一种方法是使用 defaultExpression：
@Mapping(target = "payload", source = "payload.after", defaultExpression = "java(source.getPayload().getBefore())")
TargetEntity toTarget(SourceEntity source);
英文:
From MapStruct docs I see that only you can use predefined values: https://mapstruct.org/documentation/stable/reference/html/#default-values-and-constants
But you can easily do it by using annotations like @AfterMapping or @BeforeMapping check in MapStruct docs examples
EDIT:
@Mapping(target = "otherTargetField", source = "otherSrcField")
TargetEntity toTarget(SourceEntity source);
@AfterMapping
void toTargetAfterMapping(@MappingTarget TargetEntity, SourceEntity source) {
// Your after mapping logic with payload.before and payload.after
}
MapStruct auto-resolves that this method is called at the end of the mapping method before the last return statement. If you want to know more see MapStruct docs - customising mappings with before and after.
Another approach which you can use is a defaultExpression
@Mapping(target = "payload", source = "payload.after", defaultExpression = "java(source.getPayload().getBefore())")
TargetEntity toTarget(SourceEntity source);
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