Cannot assign to read only property'type'of object'#<Banner>'`

[qualc]

In the JavaScript grammar. After an instance of the @entity () modified new object, the attribute value of the instance can not be changed
TypeError: Cannot assign to read only property'type'of object'#<Banner>'
I try to add descriptor.writable = true in Column and so on.

function Column(typeOrOptions, options) {
    return function(object, propertyName, descriptor) {
        descriptor.writable = true;
    };
}

Did I make a mistake?

[pleerock]

Sorry, but I do not understand what you mean and what you are trying to do

[qualc]

Example：
/entity/banner.js

import { Column, Entity, PrimaryGeneratedColumn } from 'typeorm';
@Entity('banner')
export class Banner {
    @PrimaryGeneratedColumn()
    id;
    @Column()
    type;
}

app.js

import "reflect-metadata";
import { Banner } from './entity/banner';
typeorm.createConnection({
     ...,
   entities: ['./entity/*.js'  ]
}).then(async function(connection) {
    let banner = new Banner();
    banner.type = 1;  // **TypeError: Cannot assign to read only property 'type' of object '#<Banner>'**
}).catch(e => {
    console.log(e)
});

[pleerock]

Looks like an issue of the transpiler plugin you are using. Does using descriptor.writable = true in decorators solve the problem?

[qualc]

Yes, it does.

[pleerock]

okay, are you able to create a pull request for this change and make sure its not breaking anything else in typescript infrastructure?

[qualc]

Emm,I need time to test it.I'll give you a reply later.

[yhpark]

I also went through this issue. Apparently the babel class-properties proposal plugin in loose mode transpiles class properties without pre-assigned value non-writable. Not sure if this is a bug or intended..

Right now one solution is to assign any default values as below (undefined works as well):

import { Column, Entity, PrimaryGeneratedColumn } from 'typeorm';
@Entity('banner')
export class Banner {
    @PrimaryGeneratedColumn()
    id = undefined;
    @Column()
    type = 1;
}

[pleerock]

After certain tests I found that it does not work in typescript. I think problem is in babel plugin and it should be resolved there. I remember I was already reporting to them this issue year ago. Closing.

[qualc]

Yes, I also found that the porblem was due to the inconsistency of bable plugin and typescript to the interpretation of decorator.