Return valid GeoJSON with Flask + GeoAlchemy2 app - json

Question

Since few days I am wondering how to make my Flask app return valid GeoJSON, here is what I got so far:
models.py
class Building(base):
__tablename__ = 'buildings'
id = Column(Integer, primary_key=True)
district = Column(Unicode)
address = Column(Unicode)
name = Column(Unicode)
building_type = Column(Unicode)
mpoly = Column(Geometry('MULTIPOLYGON'))
building = relationship("User")
# this part is done as answered here: https://stackoverflow.com/questions/41684512/cant-transform-geometry-to-geojson
def building_to_dict(self):
return mapping(shapely.wkb.loads(str(self.mpoly), True))
def __str__(self):
d = dict()
d["id"] = self.id
d["district"] = self.district
d["address"] = self.address
d["name"] = self.name
d["building_type"] = self.building_type
d["mpoly"] = self.building_to_dict()
return shapely.dumps(d)
Now at main file I have following routing:
app.py
#app.route('/geojson')
def get_json():
features = session.query(Building.mpoly.ST_AsGeoJSON()).all()
return jsonify(features)
And here are my two problems:
1)
Returned JSON-like response that looks like following:
"{\"type\":\"MultiPolygon\",\"coordinates\":[[[[16.8933137,52.471446],...,]]]}"
Is not proper GeoJSON.
Features variable before jsonify looks this way:
[('{"type":"MultiPolygon","coordinates":[[[[16.914159616,52.473822807],...,]]]}',)]
2)
How my GeoAlchemy query should look like, to return not just geometry field, but others as well?
Any kind of hints or helps highly appreciated, thanks in advance!

Answer 1

You may use marshmallow-sqlalchemy for creating json like responses.
create
schemas.py
#!schemas.py
from marshmallow import fields
from marshmallow_sqlalchemy import ModelSchema
from app.models import Building
from geoalchemy.shape import to_shape
class BuildingSchema(ModelSchema):
id = fields.Integer()
district = fileds.Unicode()
address = fileds.Unicode()
name = fields.Unicode()
building_type = fields.Unicode()
mpoly = fileds.Method("geom_to_json")
#staticmethod
def geom_to_json(obj):
mpoly = to_shape(obj.mpoly)
return {
lat: mpoly.y,
lon: mpoly.x,
#and so on ...
}
class Meta:
model = Building
exclude = ("mpoly")
bulding_schema = BuildingSchema(many=True)
after this you can use it in your views(routes)
from app.schemas import building_schema
#app.route('/geojson')
def json():
buildings = Buildings.query.all()
response = building_schema.dumps(buildings)
return response