class-transformer-shim: support metadata reflection

[haschu]

Issue type:

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

TypeORM version:

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

---

TypeORM provides a class-transformer-shim, which is awesome for browser/fronend application usage.

However, the transformation of Date types for example - or any other type, that isn't passed via a decorator and a typeFunction - requires additional class-transformer code:

@Entity()
export class Photo {

    @PrimaryGeneratedColumn()
    id: number;

    @Column()
    url: string;
    
    // Works fine => class-transformer creates User objects :)
    @ManyToOne(type => User, user => user.photos)
    user: User;
    
    // No Date object, class-transformer leaves that as string :(
    @CreateDateColumn()
    createdAt: Date;

}

To make it work, we need to write:

import { Type } from 'class-transformer';

//...

@Type(() => Date)
@CreateDateColumn()
createdAt: Date;

which I find annoying, especially when sharing entities between backend and frontend. One would also have to import the class-transformer library into his backend, but actually it's only used on the frontend side. Plus of course, it saves us lots of code lines.

We could solve this, if typeorm-class-transformer-shim.js would support metadata reflection.
If the client imports "reflect-metadata", we could use design:type and automatically pass it to the @Type decorator of class-transformer, as we already do with typeFunctions.

PR is on the way.

[Michael-Dawkins]

Huge thanks for bringing this up, I am currently "reviving" all dates individually and manually on the front end and forgetting this is often a source of bugs for us.

I am not familiar with the use of reflect-metadata, have you managed to implement a bridge from typeORM's date annotation to class-transformer ?

[haschu]

@Michael-Dawkins yes, it's already included in the latest release :)

You have to include typeorm-class-transformer-shim.js into your tsconfig.json path section:

    "paths": {
      "typeorm": [ "node_modules/typeorm/extra/typeorm-class-transformer-shim.js" ]
    }

[Michael-Dawkins]

You just made my day.

I've been thinking for months it would be nice to simply use the annotations already present from using TypeORM or heck, even typescript.
Now I can remove so much low value code from our codebase .

By reading class-transformer's doc again today, I also discovered "enableImplicitConversion"'s new option of class-transformer which is a nice addition.