Describe the bug
Ids assigned to a collection via wrap(...).assign are not persisted.

Stack trace

...

To Reproduce
Steps to reproduce the behavior:

@Entity()
export class Book2 {
  @ManyToMany({ entity: () => BookTag2, cascade: [], fixedOrderColumn: 'order' })
  tags = new Collection<BookTag2>(this);
}
...
const id1 = 1; //id of existing tag
const book

This task is for noting any missing wiki documentation that needs to be rectified.

Be sure to check the wiki before making a request for documentation.

I'm very confused about the documentation. The examples from the README.md are very minimalistic. The demo app uses very different approaches that are not documented anywhere.

I would suggest improving the docs. Without proper docs, such great lib is not as worthy as it could be.