Updating an entity using wrap(existing).assign({...new_contents}) does not update its BlobType properties.

[jjhbw]

Thanks for this excellent lib! I found something that may be a bug.

Describe the bug
Updating an entity using wrap(existing).assign({...new_contents}) does not seem to update its BlobType properties. The below code is a representation of what goes on in the backend i'm working on. I am wrap-ing the existing entity and using .assign() to assign the new properties to it. Obviously this can be simplified if you only want to assign a new contents property using book.contents = new_contents, but I also want it to update the other properties that my entity has so I'm using wrap().assign(). Updating the name property through this mechanism (which is just a varchar) seems to work fine.

Be sure to let me know if I'm misunderstanding something here!

To Reproduce

import { BlobType, Entity, MikroORM, PrimaryKey, Property, wrap } from "@mikro-orm/core"

@Entity()
export class Book {
    constructor(name: string, contents: Buffer) {
        this.name = name
        this.contents = contents
    }

    @PrimaryKey()
    id!: number

    @Property({ type: 'varchar' })
    name: string

    @Property({ type: BlobType })
    contents: Buffer
}

const test = async () => {
    const connection = await MikroORM.init({
        entities: [
            Book,
        ],
        dbName: ':memory:',
        type: 'sqlite',
        debug: true,
    })

    const generator = connection.getSchemaGenerator()
    await generator.updateSchema()
    {
        const contents = Buffer.from('abcdefg')
        const book1 = new Book('initial name', contents)
        await connection.em.fork().persistAndFlush(book1)
    }

    const new_contents_value = '123456'
    const new_name = 'updated name'
    {
        const new_version = {
            id: 1,
            name: new_name,
            contents: Buffer.from(new_contents_value),
        }
        const em = connection.em.fork()
        const existing = await em.findOneOrFail(Book, 1)
        const to_save = wrap(existing).assign({ ...new_version }, { mergeObjects: true })
        await em.persistAndFlush(to_save)
    }

    {
        const book1 = await connection.em.fork().findOneOrFail(Book, 1)
        if (book1.name !== new_name) {
            throw new Error(`expected name to be ${new_name} but instead received ${book1.name}`)
        }
        const conts = book1.contents.toString()
        if (conts !== new_contents_value) {
            throw new Error(`expected contents to be ${new_contents_value} but instead received ${conts}`)
        }
    }
}

test().catch(console.log)

Expected behavior
I would expect the BlobType buffer to contain the new value.

Versions

Dependency	Version
node	v12.20.0
typescript	4.1.3
mikro-orm	4.4.2
your-driver	sqlite3 5.0.1

[B4nan]

Drop the mergeObjects and it will work.

[jjhbw]

Awesome, thanks. I'll use that for now.

[B4nan]

Btw few notes about the code:

const existing = await em.findOneOrFail(Book, 1) // here you load the book - therefore it is a managed entity
const to_save = wrap(existing).assign({ ...new_version }, { mergeObjects: true }) // assign will return the very same entity (`to_save === existing`), also it won't mutate your data
await em.persistAndFlush(to_save) // as the entity is managed, calling flush is enough - only new entities need to be persisted

So in other words, its equivalent to this:

const book = await em.findOneOrFail(Book, 1);
wrap(book).assign(new_version, { mergeObjects: true }); // or even better `em.assign(book, new_version, { mergeObjects: true })`
await em.flush();

[jjhbw]

Thanks again! Very useful to see assign() used in context.