Using Eve Event Hooks from your Blueprint

by Pau Freixes

The use of Flask Blueprints helps us to extend our Eve applications with new endpoints that do not fit as a typical Eve resource. Pulling these endpoints out of the Eve scope allows us to write specific code in order to handle specific situations.

In the context of a Blueprint we could expect Eve features not be available, but often that is not the case. We can continue to use a bunch of features, such as Event Hooks.

Next snippet displays how the users module has a blueprint which performs some custom actions and then uses the users_deleted signal to notify and invoke all callback functions which are registered to the Eve application.

from flask import Blueprint, current_app as app

blueprint = Blueprint('prefix_uri', __name__)

@blueprint.route('/users/<username>', methods=['DELETE'])
def del_user(username):
    # some specific code goes here
    # ...

    # call Eve-hooks consumers for this  event
    getattr(app, "users_deleted")(username)

Next snippet displays how the blueprint is binded over our main Eve application and how the specific set_username_as_none function is registered to be called each time an user is deleted using the Eve events, to update the properly MongoDB collection.

from eve import Eve
from users import blueprint
from flask import current_app, request

def set_username_as_none(username):
    resource = request.endpoint.split('|')[0]
    return  current_app.data.driver.db[resource].update(
        {"user" : username},
        {"$set": {"user": None}},
        multi=True
    )

app = Eve()
# register the blueprint to the main Eve application
app.register_blueprint(blueprint)
# bind the callback function so it is invoked at each user deletion
app.users_deleted += set_username_as_none
app.run()

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