[BUG] [python-flask] invalid `.from_dict` generated when using object as query parameter

Created by: Tohnmeister

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used? 4.2.2
• Have you search for related issues/PRs?
• What's the actual output vs expected output? I would've expected this to generate code that compiles/runs. But the .from_dict seems invalid Python syntax.
• [Optional] Bounty to sponsor the fix (example)

Description

When using this spec as input:

openapi: "3.0.0"
info:
  title: "My API"
  version: "0.0.1"
paths:
  /invoices:
    get:
      parameters:
        - name: filter
          in: query
          description: Filter parameters
          required: false
          schema:
            type: object
            properties:
              field:
                type: string
      responses:
        '200':
          description: An array of invoices
          content:
            application/json:
              schema:
                type: array
                items:
                  type: object
                  properties:
                    number:
                      type: integer
                      format: int64

a default_controller.py is generated containing the following code:

import connexion
import six

from openapi_server.models.filter import Filter  # noqa: E501
from openapi_server.models.inline_response200 import InlineResponse200  # noqa: E501
from openapi_server import util


def invoices_get(filter=None):  # noqa: E501
    """invoices_get

     # noqa: E501

    :param filter: Filter parameters
    :type filter: dict | bytes

    :rtype: List[InlineResponse200]
    """
    if connexion.request.is_json:
        filter = .from_dict(connexion.request.get_json())  # noqa: E501
    return 'do some magic!'

The .from_dict is invalid Python syntax.

Trying to run the generated application, results in the following error:

jsonschema.exceptions.RefResolutionError: Unresolvable JSON pointer: 'components/parameters/filter'

openapi-generator version

4.2.2

OpenAPI declaration file content or url

See above.

Command line used for generation

openapi-generator generate -i ./openapi.yaml -g python-flask -o ./generated

Steps to reproduce

• Use above command and openapi.yaml to generate python-flask code.

Related issues/PRs

Suggest a fix

I suppose the .from_dict needs to be prefixed by a class name.