Remove add button in Django admin Many-to-many field

Question

How can I remove add button in Many-to-many field selection from Django admin?

Answer 1

def get_form(self, request, obj=None, **kwargs): 
    form = super(InvoiceOrderAdmin, self).get_form(request, obj, **kwargs)
    form.base_fields['orders'].widget.can_add_related = False
    return form

Overriding get_form inside model admin class can achieve this behavior.