Short term solution to using Neomodel 3.3.0 with Flask.

__init__.py

"""
This is a module that is supposed to be describing the whole datamodel of an application.

NOTE: The directory structure that is implied here is:

src/
    app_models/
        __init__.py (THIS FILE)
    main.py
"""
    
import neomodel

class ABaseClass(neomodel.StructuredNode):
    object_id = neomodel.UniqueIdProperty()

class SomeClass(ABaseClass):
    payload = neomodel.StringProperty()
    
class SomeOtherClass(SomeClass):
    numeric_payload = neomodel.IntegerProperty()

main.py

"""
A very simple Flask example to demonstrate saving and restoring the neomodel.db object state.
This example is related to issue #378.

Please note: 

1. This technique can be replicated as is but is more likely to lead to the development of a 
flask-neomodel-manager that will be handling the saving/restoring of the node class registry in the background.

2. The application requires the environment variables NEO4J_USERNAME, NEO4J_PASSWORD and NEO4J_BOLT_URL to be
set before it can connect to a neo4j instance.
"""

import os
import flask
from neomodel import config, db
import app_models 
# NOTE: The application's data model is loaded as a separate module to ensure that it will be made known to neomodel
#       in its entirety.
    
# Create the application
app = flask.Flask(__name__)    

# Set up its routes 
@app.route("/", methods=["GET"])
def get_all_items():
    # NOTE: PRIOR TO EXECUTING ANY DB OPERATION, RESTORE THE STATE OF THE NEOMODEL.DB OBJECT
    app_models.neomodel.db._NODE_CLASS_REGISTRY = flask.current_app.config["neomodel_db_NODE_CLASS_REGISTRY"]
    # From this point onwards, operations are executed as expected.
    return "Stuff:{}".format(" -- ".join(map(lambda x:x.payload,app_models.SomeClass.nodes.all())))
  
     
# At this point, the neomodel.db._NODE_CLASS_REGISTRY has been populated as expected
# NOTE: Save the state of neomodel.db._NODE_CLASS_REGISTRY
app.config.update(neomodel_db_NODE_CLASS_REGISTRY = db._NODE_CLASS_REGISTRY)  
config.DATABASE_URL = os.environ["NEO4J_BOLT_URL"]

    
# This is just an initialisation step that executes only during creation of the application just to make sure that
# the database is populated with some data.
app_models.neomodel.db.cypher_query("MATCH (a) detach delete a;");
app_models.SomeClass(payload="Alpha").save()
app_models.SomeClass(payload="Beta").save()
app_models.SomeClass(payload="Gamma").save()
app_models.SomeClass(payload="Delta").save()

app.run()