ForSelf

In previous sections, we've learned that we can have Auto Flattening with Naming Conventions.

Let's assume we have the following models

class Item {
    @AutoMap()
    name: string;
    @AutoMap()
    price: number;
    @AutoMap()
    stock: number;
}

class CartItem {
    @AutoMap(() => Item)
    item: Item;
    @AutoMap()
    quantity: number;
}

class CartItemDto {
    @AutoMap()
    itemName: string;
    @AutoMap()
    itemPrice: number;
    @AutoMap()
    quantity: number;

    get total() {
        return this.price * this.quantity;
    }
}

From Auto Flattening documentation, we know that CartItemDto.itemName will be mapped automatically from CartItem.item.name and CartItemDto.itemPrice will be mapped automatically from CartItem.item.price.

While that works, we want to keep out DTOs cleaner sometimes without having to prefix some fields to achieve Auto Flattening. Let's adjust our models a little

class Item {
    @AutoMap()
    name: string;
    @AutoMap()
    price: number;
    @AutoMap()
    stock: number;
}

class CartItem {
    @AutoMap(() => Item)
    item: Item;
    @AutoMap()
    quantity: number;
}

class CartItemDto {
    @AutoMap()
    name: string;
    @AutoMap()
    price: number;
    @AutoMap()
    quantity: number;

    get total() {
        return this.price * this.quantity;
    }
}

There are two approaches we can go about this

Use forMember() explicitly

createMap(
    mapper,
    CartItem,
    CartItemDto,
    forMember(
        (destination) => destination.name,
        mapFrom((source) => source.item.name)
    ),
    forMember(
        (destination) => destination.price,
        mapFrom((source) => source.item.price)
    )
);

Use forSelf()

Call forSelf() and pass in the nested model so AutoMapper will map the matching properties between the Destination and that nested model. In other words, AutoMapper creates a Mapping between the nested model and Destination then have the original Mapping extend it. The second argument lets AutoMapper knows where to find the data whose value is of type nested model.

createMap(
    mapper,
    CartItem,
    CartItemDto,
    forSelf(Item, (source) => source.item)
);

tip

forSelf() also accepts a Mapping instead of just the nested model.

const mapping = createMap(mapper, Item, CartItemDto);
createMap(
    mapper,
    CartItem,
    CartItemDto,
    forSelf(mapping, (source) => source.item)
);