ViewColumn does not take a transformer input

[rhlsthrm]

Issue type:

[ ] question
[x] bug report
[ ] feature request
[ ] documentation issue

Database system/driver:

[ ] cordova
[ ] mongodb
[ ] mssql
[ ] mysql / mariadb
[ ] oracle
[x] postgres
[ ] cockroachdb
[ ] sqlite
[ ] sqljs
[ ] react-native
[ ] expo

TypeORM version:

[x] latest
[ ] @next
[ ] 0.x.x (or put your version here)

Steps to reproduce or a small repository showing the problem:

import { BigNumber } from "bignumber.js";

@Entity()
export class Number {
  @PrimaryGeneratedColumn()
  id!: number;

  @Column("text", {
    transformer: {
      from: (value: string): BigNumber => new BigNumber(value),
      to: (value: BigNumber): string => value.toString(),
    },
  })
  big!: BigNumber;
}

@ViewEntity(`SELECT "big" from "number"`)
export class NumberView {
  @ViewColumn()
  // does not return as BigNumber type
  big: BigNumber;
}

I'd like to be able to have my view entity transform the value before returning it to my JS. Is there a way to do this?

[NestorPerez13]

Same issue here i have a simple-array stored in the DB i want to get this from a view in the array form, instead i get a string :/

[MikeMatrix]

Came across this issue today. Seems like there isn't much difference in hydrating data between @ViewColumn and @Column. There is just no types assigned in the ViewColumnOptions.
Probably going to make a PR for this very soon.

Quick and dirty workaround:
Simply add the transformer property as you would in @Column and // @ts-ignore the type error for now.
Obviously not a recommended approach, but if you really need it (as I did), this would fix it for now.

[pcnova]

Came across this issue today. Seems like there isn't much difference in hydrating data between @ViewColumn and @Column. There is just no types assigned in the ViewColumnOptions. Probably going to make a PR for this very soon.

Quick and dirty workaround: Simply add the transformer property as you would in @Column and // @ts-ignore the type error for now. Obviously not a recommended approach, but if you really need it (as I did), this would fix it for now.

To avoid the unsightly // @ts-ignore (which, if you're using ESLint, will force you to add another // eslint-disable-next-line comment on top), I found out you can also do this:

@ViewColumn({
    transformer: { from: val => new BigNumber(val) },
  } as ColumnOptions)
big: BigNumber;

[IanGYan]

transformer should be an instance of a class which implements ValueTransformer or instances array.

import { ViewColumnOptions } from "../options/ViewColumnOptions";
/**
 * ViewColumn decorator is used to mark a specific class property as a view column.
 */
export declare function ViewColumn(options?: ViewColumnOptions): PropertyDecorator;

import { ValueTransformer } from "./ValueTransformer";
/**
 * Describes all view column's options.
 */
export interface ViewColumnOptions {
    /**
     * Column name in the database.
     */
    name?: string;
    /**
     * Specifies a value transformer(s) that is to be used to unmarshal
     * this column when reading from the database.
     */
    transformer?: ValueTransformer | ValueTransformer[];
}

/**
 * Interface for objects that deal with (un)marshalling data.
 */
export interface ValueTransformer {
    /**
     * Used to marshal data when writing to the database.
     */
    to(value: any): any;
    /**
     * Used to unmarshal data when reading from the database.
     */
    from(value: any): any;
}

Write a transformer such as export class NumToBig implements ValueTransformer { ... }, then pass the instance to transformer.