Patch operation - mapper output sets fields as undefined where not present in source

[jbeckton]

This issue seems out of the blue, I remember this working properly after updating to v7 but now all the sudden mapped object contains fields with a value of undefined where they did not exist in the source object.

When I send a patch operation to my api the dto may only contain the fields I want to update, the mapped output contains the missing fields with values set to undefined. This is causing the collection document fields to be changed to null which is very bad since the data is now lost.

I am hoping that I made a mistake somewhere but I don't remember having to do anything after the v7 install to get the missing source fields to be ignored in the destination. This can be a huge problem in production causing data loss, I need to figure out if the mapper lib just doesn't work this way anymore or that I inadvertently changed something to cause this behavior.

SectionDto { feature: 'listings', slug: 'hello-slug' }

SectionMongoDocument { feature: 'listings', slug: 'hello-slug', name: undefined, order: undefined, published: undefined, description: undefined, icon: undefined, categories: undefined }

[nartc]

That definitely sounds like a regression. Would you mind providing a quick simple reproduce so I can take a closer look?

[jbeckton]

AutomapperModule.forRoot({
      options: [{ name: 'sections', pluginInitializer: classes, errorHandler: new MapperErrorHandler() }],
      singular: false
    }),

export class SectionMongoDto {
  id?: string;
  @AutoMap()
  feature?: string;
  @AutoMap()
  slug?: string;
  @AutoMap()
  name?: string;
  @AutoMap()
  order?: number;
  @AutoMap()
  published?: boolean;
  @AutoMap()
  description?: string;
  @AutoMap()
  icon?: string;
  @AutoMap({ typeFn: () => CategoryMongoDto })
  categories?: CategoryMongoDto[];
}

export class SectionMongoDocument {
  _id?: ObjectId;
  __v?: number;
  @AutoMap()
  feature?: string;
  @AutoMap()
  slug?: string;
  @AutoMap()
  name?: string;
  @AutoMap()
  order?: number;
  @AutoMap()
  published?: boolean;
  @AutoMap()
  description?: string;
  @AutoMap()
  icon?: string;
  @AutoMap({ typeFn: () => CategoryMongoDocument })
  categories?: CategoryMongoDocument[];
}

mapper.createMap(SectionMongoDto, SectionMongoDocument).forMember((d) => d.categories, ignore());

const patchSectionDto = {
    "feature": "listings",
    "slug": "my-slug"
}
const sectionDocument = this.sectionMapper.map(patchSectionDto, SectionMongoDocument, SectionMongoDto);

[jbeckton]

I am currently using 7.2.1 but I upgraded when I noticed this issue, I was on ^7.0.2 so it could have started with one of the minor version updates. I will gladly provide more info upon request, I enjoyed using your library as it saved me a lot of time and code. I can't risk the data loss due to regression bugs so i'm gonna switch to Morphism. Best of luck.

[jbeckton]

removeEmpty is a function I wrote to strip properties from the object that contain undefined values

export const removeEmpty = (obj) => {
  const newObj = {};
  Object.keys(obj).forEach((key) => {
    if (obj[key] === Object(obj[key])) newObj[key] = removeEmpty(obj[key]);
    else if (obj[key] !== undefined) newObj[key] = obj[key];
  });
  return newObj;
};

[nartc]

@jbeckton afterMap() uses the references to the source and destination. So you can mutate the destination directly

const categoryDocument = this.sectionMapper.map<CategoryMongoDto, CategoryMongoDocument>(
      patchCategoryDto,
      CategoryMongoDocument,
      CategoryMongoDto,
      {
        afterMap: (_, destination) => {
            for (const key of Object.keys(destination)) {
               if (destination[key] === undefined) {
                  delete destination[key];
               }
            }
        }
      }
    );

this should work

[jbeckton]

@nartc so wouldn't just reassigning it work then?

const categoryDocument = this.sectionMapper.map<CategoryMongoDto, CategoryMongoDocument>(
      patchCategoryDto,
      CategoryMongoDocument,
      CategoryMongoDto,
      {
        afterMap: (source, destination) => {
            destination = removeEmpty(destination);
        }
      }
    );

[jbeckton]

I guess reassignment does not work... Here is a function that supports recursion for nested objects and it works as expected.

export const removeUndefinedFromRef = (obj) => {
  Object.keys(obj).forEach((key) => {
    if (obj[key] === Object(obj[key])) {
      removeUndefinedFromRef(obj[key]);
    } else if (obj[key] === undefined) {
      delete obj[key];
    }
  });
};

[nartc]

@jbeckton no because removeEmpty() returns a new reference. Pointing destination to a new reference doesn't work in the case of afterMap() here.

Yeah. That should work. You can attach that on createMap()

mapper.createMap(CaterogyMongoDto, CategoryMongoDocument)
   .afterMap(removeUndefinedFromRef);

This will run on every map you have for mapper.map(dto, CategoryMongoDocument, CategoryMongoDto) without having to attach afterMap() on the .map() operation. Of course, attaching the callback on .map() gives you better control and I guess easier to debug :)