MapStruct：使用 updateMethod() 进行初始化，即使源为 null 也可以创建

Question

有人可以告诉我如何（或者是否有可能）强制更新方法创建目标（如果它为空）？

我想实现这样的目标：

    @BeforeMapping
    @Mapping(source = "inputBy", target = "tactical.inputBy")
    default BCSecuritiesTrade updateOrCreateInputBy(String inputBy, @MappingTarget BCSecuritiesTrade bcSecuritiesTrade){
        return bcSecuritiesTrade != null? bcSecuritiesTrade:new BCSecuritiesTrade();
    }

但这总是返回新实例并且不进行映射。

我想要一个方法，当它存在时更新“目标”并在输入 null 时创建新的“目标”对象。

此外，当“源”对象为空时，它不应返回空值，但“目标”对象或如果“目标”对象为空则创建新对象。当前方法在 "source" 为 null 时返回 null。

非常感谢！

Answer 1

我还没有找到开箱即用的解决方案。 根据documentation，似乎 MapStruct 被设计为仅将updateMethod 用于现有实例。
我通过其他自定义方法解决了问题。

MapStruct 版本 1.4.2.Final

@Mapper
public interface BCSecuritiesTradeMapper {
    BCSecuritiesTradeMapper INSTANCE = Mappers.getMapper(BCSecuritiesTradeMapper.class);

    @Mapping(source = "inputBy", target = "tactical.inputBy")
    BCSecuritiesTrade updateInputBy(String inputBy, @MappingTarget BCSecuritiesTrade bcSecuritiesTrade);

    default BCSecuritiesTrade updateOrCreateInputBy(String inputBy, BCSecuritiesTrade bcSecuritiesTrade) {
        if (bcSecuritiesTrade == null) {
            bcSecuritiesTrade = new BCSecuritiesTrade();
        }
        if (inputBy == null) {
            return bcSecuritiesTrade;
        }
        return updateInputBy(inputBy, bcSecuritiesTrade);
    }
}

生成的代码：

public class BCSecuritiesTradeMapperImpl implements BCSecuritiesTradeMapper {
    @Override
    public BCSecuritiesTrade updateInputBy(String inputBy, BCSecuritiesTrade bcSecuritiesTrade) {
        if ( inputBy == null ) {
            return null;
        }
        if ( bcSecuritiesTrade.tactical == null ) {
            bcSecuritiesTrade.tactical = new Tactical();
        }
        stringToTactical( inputBy, bcSecuritiesTrade.tactical );

        return bcSecuritiesTrade;
    }

    protected void stringToTactical(String string, Tactical mappingTarget) {
        if ( string == null ) {
            return;
        }
        mappingTarget.inputBy = string;
    }
}

MapStruct 版本 1.5.0.RC1
新版本有更好的实现。如果source 是null，则返回target，但在传递null 的情况下仍然无法创建target 对象的实例。
自定义方法被简化但没有消除。

@Mapper
public interface BCSecuritiesTradeMapper {
    BCSecuritiesTradeMapper INSTANCE = Mappers.getMapper(BCSecuritiesTradeMapper.class);

    @Mapping(source = "inputBy", target = "tactical.inputBy")
    BCSecuritiesTrade updateInputBy(String inputBy, @MappingTarget BCSecuritiesTrade bcSecuritiesTrade);

    default BCSecuritiesTrade updateOrCreateInputBy(String inputBy, BCSecuritiesTrade bcSecuritiesTrade) {
        if (bcSecuritiesTrade == null) {
            bcSecuritiesTrade = new BCSecuritiesTrade();
        }
        return updateInputBy(inputBy, bcSecuritiesTrade);
    }
}

生成的代码：

public class BCSecuritiesTradeMapperImpl implements BCSecuritiesTradeMapper {

    @Override
    public BCSecuritiesTrade updateInputBy(String inputBy, BCSecuritiesTrade bcSecuritiesTrade) {
        if ( inputBy == null ) {
            return bcSecuritiesTrade;
        }
        if ( bcSecuritiesTrade.tactical == null ) {
            bcSecuritiesTrade.tactical = new Tactical();
        }
        stringToTactical( inputBy, bcSecuritiesTrade.tactical );
        return bcSecuritiesTrade;
    }

    protected void stringToTactical(String string, Tactical mappingTarget) {
        if ( string == null ) {
            return;
        }
        mappingTarget.inputBy = string;
    }
}

单元测试：

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

@RunWith(JUnit4.class)
public class MapperTest {
    @Test
    public void test() {
        BCSecuritiesTrade bcSecuritiesTrade = BCSecuritiesTradeMapper.INSTANCE.updateOrCreateInputBy(null, null);
        Assert.assertNotNull(bcSecuritiesTrade);
        Assert.assertNull(bcSecuritiesTrade.tactical);

        BCSecuritiesTrade bcSecuritiesTradeUpdate = BCSecuritiesTradeMapper.INSTANCE.updateOrCreateInputBy(null, bcSecuritiesTrade);
        Assert.assertNotNull(bcSecuritiesTradeUpdate);
        Assert.assertNull(bcSecuritiesTradeUpdate.tactical);
        Assert.assertEquals(bcSecuritiesTrade, bcSecuritiesTradeUpdate);

        bcSecuritiesTrade = BCSecuritiesTradeMapper.INSTANCE.updateOrCreateInputBy("123", null);
        Assert.assertNotNull(bcSecuritiesTrade);
        Assert.assertEquals(bcSecuritiesTrade.tactical.inputBy, "123");

        bcSecuritiesTradeUpdate = BCSecuritiesTradeMapper.INSTANCE.updateOrCreateInputBy("124", bcSecuritiesTrade);
        Assert.assertNotNull(bcSecuritiesTradeUpdate);
        Assert.assertEquals(bcSecuritiesTradeUpdate.tactical.inputBy, "124");
        Assert.assertEquals(bcSecuritiesTrade, bcSecuritiesTradeUpdate);

    }
}

使用的实体：

public class BCSecuritiesTrade {
    public Tactical tactical;
}

public class Tactical {
    public String inputBy;
}

替代解决方案：
为Create 和Update 创建两个单独的方法。

@Mapper(nullValueMappingStrategy = NullValueMappingStrategy.RETURN_DEFAULT)
public interface BCSecuritiesTradeMapper {
    BCSecuritiesTradeMapper INSTANCE = Mappers.getMapper(BCSecuritiesTradeMapper.class);

    @Mapping(source = "inputBy", target = "tactical.inputBy")
    BCSecuritiesTrade updateInputBy(String inputBy, @MappingTarget BCSecuritiesTrade bcSecuritiesTrade);

    @Mapping(source = "inputBy", target = "tactical.inputBy")
    BCSecuritiesTrade createInputBy(String inputBy);
}