Choosing to overload the plainToClass function may result in a type error

Question

Choosing to overload the plainToClass function may result in a type error

I've been tasked with compiling an angular project that contains mostly code written by someone else.

Although the example below compiles successfully on one machine, it throws an error on different machines.

import { plainToClass } from 'class-transformer';

plainToClass(MyClass, myObject).filter(true);

When I run ng build, I receive the following error message:

error TS2339: Property 'filter' does not exist on type 'MyClass'.

The variable myObject is defined as any but actually holds an array. By modifying the code like this, it works:

plainToClass(MyClass, myObject as any[]).filter(true);

This issue can be found throughout the entire project.

I'm puzzled as to why the same code functions properly on one machine but not on another.

Both machines are using version 0.2.0 of class-transformer in the same package.json.

It appears that one version of the method is being selected on one machine while a different one is chosen on the other. This seems to occur randomly.

Is there a way to address this problem universally?

angular typescript class-transformer

Answer 1

Answer №1

I'm not entirely sure how I can assist you, but here are some ideas that might be of help. The plainToClass method is defined as:

export function plainToClass<T, V>(cls: ClassType<T>, plain: V[], options?: ClassTransformOptions): T[];
export function plainToClass<T, V>(cls: ClassType<T>, plain: V, options?: ClassTransformOptions): T;
export function plainToClass<T, V>(cls: ClassType<T>, plain: V|V[], options?: ClassTransformOptions): T|T[] {
    return classTransformer.plainToClass(cls, plain as any, options);
}

source: https://github.com/typestack/class-transformer/blob/develop/src/index.ts

If you define myObject as any, the plainToClass function may struggle to determine which implementation to use. This could lead the compiler to assume that you are utilizing:

export function plainToClass<T, V>(cls: ClassType<T>, plain: V, options?: ClassTransformOptions): T;

which lacks the filter method because it doesn't return an array.

To resolve this, declare myObject as any[] or modify your usage of plainToClass like so:

plainToClass<any[]>(MyClass, myObject).filter(true); // added <any[]>

This adjustment enables the compiler to recognize the correct method to use (the one returning an array), allowing you to utilize .filter accordingly.

An alternative approach could involve creating a custom plainToClass function that specifically returns an array and utilizes the appropriate method from the class-transformer package/library.

These suggestions are just speculations, but hopefully, they offer some assistance.

Answer 2

I'm not entirely sure how I can assist you, but here are some ideas that might be of help. The plainToClass method is defined as:

export function plainToClass<T, V>(cls: ClassType<T>, plain: V[], options?: ClassTransformOptions): T[];
export function plainToClass<T, V>(cls: ClassType<T>, plain: V, options?: ClassTransformOptions): T;
export function plainToClass<T, V>(cls: ClassType<T>, plain: V|V[], options?: ClassTransformOptions): T|T[] {
    return classTransformer.plainToClass(cls, plain as any, options);
}

source: https://github.com/typestack/class-transformer/blob/develop/src/index.ts

If you define myObject as any, the plainToClass function may struggle to determine which implementation to use. This could lead the compiler to assume that you are utilizing:

export function plainToClass<T, V>(cls: ClassType<T>, plain: V, options?: ClassTransformOptions): T;

which lacks the filter method because it doesn't return an array.

To resolve this, declare myObject as any[] or modify your usage of plainToClass like so:

plainToClass<any[]>(MyClass, myObject).filter(true); // added <any[]>

This adjustment enables the compiler to recognize the correct method to use (the one returning an array), allowing you to utilize .filter accordingly.

An alternative approach could involve creating a custom plainToClass function that specifically returns an array and utilizes the appropriate method from the class-transformer package/library.

These suggestions are just speculations, but hopefully, they offer some assistance.

Choosing to overload the plainToClass function may result in a type error

Answer №1

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