Nestjs: Cast complex Entity to Dto

Question

I'm trying to cast a complex Entity to a Dto. I would like to remove some values which are in the entity from the DTO.

My entity looks like this (For simplicity a large part of the entity is omitted):

export class ResultEntity {
    constructor(
        public id: string,
        public userId: string,
        public results: CalculationOutputEntity[] = [],
        public item: Item = new Item(),
    ) { }
}

export class Item {
    constructor(
        public privat: Private = new Private(),
        public state: State = new State(),
        public combined: number = 0,
    ) { }
}

export class State {
    constructor(
        public numberA: number = 0,
        public numberB: number = 0,
        public numberC: number = 0,
        public numberD: number = 0,
    ) { }
}

I have found a solution which works very well for simple entities: Cast entity to dto If I adopt this suggestion of the custom interceptor, removing the id or the whole item property works.

I have tried two possibilities tot define my DTOs:

1. It returns only the id and the item as a whole.

@Exclude()
export class AdvisoryResultDto {
    @Expose()
    public id: string;
    public userId: string;
    public results: CalculationOutputDto[];
    @Expose()
    public item: Item;
}

2. This solution returns everything except the item property.

export class AdvisoryResultDto {
    public id: string;
    public userId: string;
    public results: CalculationOutputDto[];
    @Exclude()
    public item: Item;
}

The problem now is that I want to remove only certain values within the item property. So for example the private field and within the state-property numberB.

I would like to have the possibility within the nested classes to remove single values also with Exclude().

So for example:

export class AdvisoryResultDto {
    public id: string;
    public userId: string;
    public results: CalculationOutputDto[];
    public item: Item;
}

export class Item {
    @Exclude()
    public privat: PrivateDto;
    public state: StateDto;
    public combined: number;
}

export class StateDto {
    public numberA: number;
    @Exclude()
    public numberB: number;
    public numberC: number;
    public numberD: number;
}

Unfortunately I can't find anything about this exact problem. To take over the mapping manually would also not be a solution, since the CalculationOutput is by far more complex and is nested with many classes and properties.

Am I just missing a small step or is it not possible with Expose and Exclude from the class-transformer? If not I would appreciate another solution.

Answer 1

So i found the soulution in the documentation of the class-transformer package: https://github.com/typestack/class-transformer#working-with-nested-objects

I need to add the @Type-Decorator to nested classes

The solution:

@Expose()
export class AdvisoryResultDto {
    public id: string;
    public userId: string;
    public results: CalculationOutputDto[];
    @Type(() => Item)
    public item: Item;
}

export class Item {
    @Exclude()
    @Type(() => PrivateDto)
    public privat: PrivateDto;
    @Expose()
    @Type(() => StateDto)
    public state: StateDto;
    public combined: number;
}

export class StateDto {
    public numberA: number;
    @Exclude()
    public numberB: number;
    public numberC: number;
    public numberD: number;
}