CODEWITHSUNDEEP
pythonflaskflask-restful
zooole
zooole

Reputation: 149

Errorhandler is not called for custom exception

I have the following error handlers:

@api.errorhandler(DatabaseException)
    def handle_database_exception(database_error):
        return database_error.query_error, 400


@api.errorhandler(ValidationException)
    def handle_validation_exception(validation_error):
        return {'fields': validation_error.body_error}, 400

These are simple classes:

class ValidationException(Exception):

    def __init__(self, body_error=None, missing_files=None):
        Exception.__init__(self, "Validation failed")
        self.body_error = body_error
        if missing_files is not None:
            for missing_file in missing_files:
                self.body_error[missing_file] = ['required file']

class DatabaseException(Exception):

    def __init__(self, details):
        Exception.__init__(self, "Database Error")
        self.query_error = details

Here's my problem: If I call raise the DatabaseException in any of my routes, it falls through and I get a 500 template from flask.

The really funny thing is that the ValidationException, which was implemented earlier works just fine.

I went through in detail what's going on, when the ValidationException is raised, it goes through response.py and ends up in the error handler. I'm unfortunately can't comprehend everything that's going on deep inside flask, but in debug, the DatabaseException is certainly went on a different route.

I expect that the error handlers get called. If I raise a DatabaseException in one of my routes, it should get called.

Upvotes: 0

Views: 80

Answers (2)

Atrist Unknown
Atrist Unknown

Reputation: 36

Sorry, my answer was a bit strange. If you want to return a JSON response, you could do it like this. 

class ValidationException(Exception):
    def __init__(self, body_error=None, missing_files=None):
        Exception.__init__(self, "Validation failed")
        self.body_error = body_error
        if missing_files is not None:
            for missing_file in missing_files:
            self.body_error[missing_file] = ['required file']

@api.errorhandler(ValidationException)
def handle_validation_exception(validation_error):
    from flask import jsonify, make_response
    return make_response(jsonify({'fields': validation_error.body_error}), 400)

This way is also possible.

@api.errorhandler(ValidationException)
def handle_validation_exception(validation_error):
    return "{'fields': validation_error.body_error}", 400

The DatabaseException works fine and returns 400 Bad Request with a plaintext body.

Have fun ^2.

Upvotes: 2

Artist Unknown
Artist Unknown

Reputation: 11

DatabaseException worked perfectly for me.

In the second solution, you try to return a Python dictionary. I assume that the missing quotes cause the error. Maybe you could use jsonify and make_response.

@api.errorhandler(DatabaseException)
def handle_validation_exception(validation_error):
    from flask import jsonify, make_response
    return make_response(jsonify({ 'fields': validation_error.query_error }), 400)

Have fun!

Upvotes: 1

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