Problem
I am building an app on Flask, Flask-SQLAlchemy, and Flask-Restless. I have used restless to generate an API for a parent-child-grandchild relationship*. A GET on my child will correctly fetch the grandchild, but a GET on the parent will not fetch the grandchild for each child.
*In fact, the parent-child relationship is a many-to-many, but same premise.
Models
class Grandchild(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, nullable=False)
parent = db.relationship('Child', backref='grandchild')
parent_child = db.Table('parent_child',
db.Column('parent_id', db.Integer, db.ForeignKey('parent.id')),
db.Column('child_id', db.Integer, db.ForeignKey('child.id')),
db.Column('number', db.SmallInteger)
)
class Child(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, nullable=False)
grandchild_id = db.Column(db.Integer, db.ForeignKey('grandchild.id'), nullable=False)
class Parent(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, nullable=False)
children = db.relationship('Child', secondary=parent_child)
api.create_api(Child, exclude_columns=['grandchild_id'])
api.create_api(Parent)
GET: /api/child response
{
"num_results": 1,
"objects": [
{
"id": 1,
"name": "test"
"grandchild": {
"id": 1,
"name": "test"
}
}
],
"page": 1,
"total_pages": 1
}
GET: /api/parent response
{
"num_results": 1,
"objects": [
{
"children": [
{
"id": 1,
"name": "test",
"grandchild_id": 1
}
],
"id": 1,
"name": "test"
}],
"page": 1,
"total_pages": 1
}
postprocessors can be used to fetch grandchild.
def parent_post_get_many(result=None, search_params=None, **kw):
for object in result['objects']:
for child in object['children']:
grandchild = Grandchild.query.get(child['grand_child_id'])
child.update({'grandchild': grandchild})
api.create_api(Parent, postprocessors={'GET_MANY': [parent_post_get_many]})
After looking at this for a few hours I'm going to give the best answer I have at the moment. I've tried a number of approaches and haven't been able to get anything to successfully render the grandchild, so I turned to the flask-restless issues tracker to see what I could find:
https://github.com/jfinkels/flask-restless/pull/222#issuecomment-31326359 and @jfinkels response seem to indicate that what you want is currently not possible in flask-restless.
Assuming my assessment of the state of issues is correct, you may want to look into either designing around this issue, or using a different package to serve your API (perhaps Flask-restful, though I admit I haven't used it and don't know if it's suitable).
FWIW, I've been using Flask-Classy to build a json API for a project I'm working on. The process is a little more involved than I suspect you want, but it also comes with enough freedom to better control what queries are used and how the results are serialized.
来源:https://stackoverflow.com/questions/22707223/flask-sqlalchemy-and-flask-restless-not-fetching-grandchildren