form_ajax_refs to model with primary key attribute not matching the column in the DB

[vstoykov]

When I have the following models:

class Country(db.Model):

    name = db.Column(db.Text)
    alpha2 = db.Column('iso3166alpha2', db.Text)
    alpha3 = db.Column('iso3166alpha3', db.Text)
    numeric = db.Column('iso3166numeric', db.Integer, primary_key=True, autoincrement=False)


class Customer(db.Model):
    id = db.Column('customer_id', db.Integer, primary_key=True, nullable=False)
    name = db.Column(db.Text)
    country_number = db.Column('country', db.Integer, db.ForeignKey('country.iso3166numeric'), nullable=False)
    country = db.relationship('Country', foreign_keys=country_number)

And I try to register Customer model in administration like that

class CustomerModelView(StaffModelView):
    form_ajax_refs = {
        'country': {
            'fields': ['alpha3', 'name'],
            'page_size': 10
        }
    }

I receive an error:

AttributeError: 'Country' object has no attribute 'iso3166numeric'

The problem is obviously that attribute name of the primary key of the Country model does not match the name of the column. But it is supported by the SQLAlchemy.

The problem occurs in QueryAjaxModelLoader.format method https://github.com/flask-admin/flask-admin/blob/v1.3.0/flask_admin/contrib/sqla/ajax.py#L50-L54

I found that in SQLAlchemy there is a way to get the value of primary key by using primary_key_from_instance method of the Mapper

I will try to provide a pull request to show what I mean.

[vstoykov]

My PR #1073 has changes for fixing this issue.