Saving rdflib.Graph into a dictionary

Question

I would like to save an rdflib.Graph into the session dictionary within my Flask application as I need to access it from other route functions. The code is as follows.

from rdflib import Graph
from flask import Flask, session
import os


app = Flask(__name__)
UPLOAD_FOLDER = 'static/uploads'
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
app.config["allowed_file_extensions"] = ["ttl"]
app.config['SEND_FILE_MAX_AGE_DEFAULT'] = 0
app.secret_key = os.urandom(24)


class API:

    def __init__(self):
        app.run(host="127.0.0.1", port="5000", threaded=True, debug=True)

    @app.route("/")
    def validate_RDF():
        # saving graph to session 
        graph = Graph().parse("valid_mapping.ttl", format="ttl")
        session["graph"] = graph
        return "testing"


if __name__ == "__main__":
    # start api
    API()

Which outputs the following.

TypeError: Object of type 'Graph' is not JSON serializable

Any advice would be greatly appreciated.

Answer 1

As a rdf graph can be large, it is anyway not a good idea to try to store it in the session in my opinion. You should rather use some kind of triple store to manage your rdf information (like a web site is using a database to store information. See for instance RDFlib 'on disk' store for a store on your web server disk, or for production you would even use a triple store hosted elsewhere.