Flask restless вложенность?

Доброго дня!

Столкнулся с проблемой:

class Item(db.Model):
    id = Column(Integer, primary_key=True)
    title = Column(Text, unique=False)
    field = relationship("Field")

class Field(db.Model):
    id = Column(Integer, primary_key=True)
    name = Column(Text, unique=False)
    measurement = relationship("Measurement")
    item_id = Column(Integer, ForeignKey('item.id'))

class Measurement(db.Model):
    id = Column(Integer, primary_key=True)
    name = Column(Text, unique=False)
    field_id = Column(Integer, ForeignKey('field.id'))

api_manager = APIManager(app, flask_sqlalchemy_db=db)
api_manager.create_api(Item, methods=['GET', 'POST', 'DELETE', 'PUT'])

При обращении к api/item получаю:

{
"num_results": 2, 
"objects": [
    {
    "field": [
    {
        "id": 1, 
        "item_id": 1, 
        "name": "fild1"
    }, 
    {
        "id": 2, 
        "field_id": 1, 
        "name": "fild2"
    }
], 
    "id": 1, 
    "title": "mes#1"
}, 
{
"field": [
    {
        "id": 3, 
        "item_id": 2, 
        "name": "fildd1"
    }, 
    {
        "id": 4, 
        "lab_id": 2, 
        "name": "fildd2"
    }
], 
    "id": 2, 
    "title": "mes#2"
    }
], 
"page": 1, 
"total_pages": 1
}

Т.е. в поле Field нет поля Measurement. Как быть?