TypeScript错误：无效无法分配给参数类型

Question

I am getting this error in TypeScript:

Argument type (response: Response<DSBMannschaftDTO[]>) => void is not
  assignable to parameter type ((value:Response<DSBMannschaftDTO[]>) =>
  (PromiseLike<void> | void)) null | undefined | undefined

This is my schema:

export class DsbMannschaftDTO implements DataTransferObject {   
    id: number;   
    vereinId: number;   
    nummer: number;   
    benutzerId: number;   
    veranstaltungsId: number;   
    version: number;

    static copyFrom(optional: {
        id?: number,
        vereinId?: number,
        nummer?: number,
        benutzerId?: number;
        veranstaltungsId: number;
        version?: number  
    } = {}): DsbMannschaftDTO {
        const copy = new DsbMannschaftDTO();
        copy.id = optional.id || null;
        copy.vereinId = optional.vereinId || null;
        copy.benutzerId = optional.benutzerId || null;
        copy.veranstaltungsId = optional.veranstaltungsId || null;
        copy.nummer = optional.nummer || null;
        copy.version = optional.version || null;

        return copy;
    }
}

and this is my code

private loadTableRows() {
    this.loading = true;

    this.dsbMannschaftDataProvider.findAll()
        .then(onfulfilled:(response: Response<DsbMannschaftDTO[]>) => this.handleLoadTableRowsSuccess(response))
        .catch(onrejected:(response: Response<DsbMannschaftDTO[]>) => this.handleLoadTableRowsFailure(response));
}

What exactly does this error mean? Thank you very much in advance

Answer 1

The problem here is your object definition. You defined DsbMannschaftDTO like:

id: number; <- value has to be a number
vereinId: number;   <- value has to be a number

and so on. Now you pass the options object with the definition:

id?: number, <- number or undefined
vereinId?: number, <- number or undefined

this is the first missmatch to number . number | undefined number | undefined is not assignable to number .

And then you write:

copy.id = optional.id || null; <- copy.id can now be number or undefined or null.

This is the second missmatch to number . number | undefined | null number | undefined | null is not assignable to number .

To fix this, replace the null with 0 (better to say with a type matching default).