Multiple backref cannot access object property on One to Many relationship SQLAlchemy - flask

Question

In the following snippet I put a template similar to my implementation. Where we have a "Grandparent" object with a OneToMany relationship with the "Parent" object and this the same relationship with the "Child" object.
class Grandparent(db.Model):
id = db.Column(db.Integer, primary_key=True, autoincrement=True, nullable=False)
name = db.Column(db.String(50), nullable=False, unique=True)
parents = db.relationship('Parent', backref='grandparent')
class Parent(db.Model):
id = db.Column(db.Integer, primary_key=True, autoincrement=True, nullable=False)
name = db.Column(db.String(50), nullable=False, unique=True)
grandparent_id = Column(Integer, ForeignKey('grandparent.id'))
children = db.relationship('Child', backref='parent')
class Child(db.Model):
id = db.Column(db.Integer, primary_key=True, autoincrement=True, nullable=False)
name = db.Column(db.String(50), nullable=False, unique=True)
parent_id = Column(Integer, ForeignKey('parent.id'))
What I want to do is get a list through the child object with information from the father and grandfather. The jinja code is as follows:
<table>
<thead>
<tr>
<th>Children name</th>
<th>Parent name</th>
<th>Grandparent name</th>
</tr>
</thead>
<tbody>
{% for child in children %}
<tr>
<td>{{ child.name }}</td>
<td>{{ child.parent.name }}</td>
<td>{{ child.parent.grandparent.name }}</td>
</tr>
{% endfor %}
</tbody>
</table>
I get the following error:
jinja2.exceptions.UndefinedError: 'None' has no attribute 'grandparent'
It fails when performing the 2 backref, I don't know how it should be done correctly, since in the official guide it is implemented in this way.
def add(model, **kwargs):
instance = model(**kwargs)
db.session.add(instance)
db.session.commit()
def getAll(model):
data = model.query.all()
return data
I use the function above to get all the objects from the database or add a new one.
So when the endpoint is reached I do the following:
#bp.route('/example/')
def example():
children = getAll(Child)
return render_template('index.html', children=children)
Solution: all objects must have associated parent.