Extending ReferenceManyField with new type cause dupes choices to appear

[armellarcier]

Hi!
I managed to extend ReferenceManyField like this :

import ReferenceManyField from 'admin-config/lib/Field/ReferenceManyField';
class ReferenceManyCustomField extends ReferenceManyField {
    constructor(name) {
        super(name);
        this._type = 'reference_many_custom';
    }
}
export default ReferenceManyCustomField;

But now the choices displayed include the current field value.
If I remove the line where I change the _type property, it goes back to normal.
Any hints on why this is happening?

[armellarcier]

If that's ok I'll submit a PR where ReferenceRefresher will check the field's removeDuplicateReferences method :

if (field.type() === 'reference_many' || field.type() === 'choices' || ( field.removeDuplicateReferences && field.removeDuplicateReferences() ) ) {
    promise = promise.then(formattedResults => this._removeDuplicates(formattedResults, currentValue));
}

[armellarcier]

I could also add the method to reference_many and choices fields in admin-config?
Well that would mean updating react-admin also so...

[jpetitcolas]

Indeed, such a _shouldRemoveDuplicate field is a more robust way to handle that. I'm 👍 with it.

[Kmaschta]

Related to #1225