如果源为空，如何防止 MapStruct 创建实体？

Question

Is there a way to prevent MapStruct from creating an object if the source is null?

Existing answers I've found explain how to do it with the object but not in a nested path. Here is an example.

The mapper

@Mapping(target = "manufacturer.id", source = "manufacturerId")
CarEntity toEntity(CarDTO carDto);

The generated code, in comments what Mapstruct misses

protected ManuFacturerEntity carDTOToCarEntity(CarDTO carDto) {
    if ( carDto == null ) {
        return null;
    }

    // what I'd like mapstruct to generate
    if (cardDto.manufacturerId == null) {
        return null;
    }

    ManufactureurEntity manufacturerEntity = new ManufacturerEntity();
    manufactureurEntity.id = carDto.manufacturerId;
    return panneaumanufacturerEntity;
}

I know I probably can do it with @BeforeMapping but it doesn't just feel the right way to do it.

Answer 1

You can change the mapping target to manufacturer and define a default method for mapping the manufacturerId to the ManufacturerEntity object that creates the object only if manufacturerId is not null .

@Mapping(target = "manufacturer", source = "manufacturerId")
CarEntity toEntity(CarDTO carDto);

default ManufacturerEntity mapManufacturerId(Long manufacturerId){
    if (manufacturerId == null) return null;
    ManufacturerEntity manufacturerEntity = new ManufacturerEntity();
    manufacturerEntity.id = manufacturerId;
    return manufacturerEntity;
}