MySQL Support

[nniehoff]

Environment

• Python version: 3.7
• Nautobot version: 1.1.2
• nautobot-capacity-metrics version: 1.0.1

Expected Behavior

Capacit metrics works with MySQL Backend

Observed Behavior

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 171, in _get_response
    response = middleware_method(request, callback, callback_args, callback_kwargs)
  File "/usr/local/lib/python3.6/site-packages/newrelic/hooks/framework_django.py", line 242, in wrapper
    return wrapped(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/dolt/middleware.py", line 50, in process_view
    return view_func(request, *view_args, **view_kwargs)
  File "/usr/local/lib/python3.6/site-packages/newrelic/hooks/framework_django.py", line 562, in wrapper
    return wrapped(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/nautobot_capacity_metrics/api/views.py", line 88, in AppMetricsView
    return ExportToDjangoView(request, view="app-metrics")
  File "/usr/local/lib/python3.6/site-packages/nautobot_capacity_metrics/api/views.py", line 77, in ExportToDjangoView
    metrics_page = prometheus_client.generate_latest(registry)
  File "/usr/local/lib/python3.6/site-packages/prometheus_client/exposition.py", line 177, in generate_latest
    for metric in registry.collect():
  File "/usr/local/lib/python3.6/site-packages/prometheus_client/registry.py", line 83, in collect
    for metric in collector.collect():
  File "/usr/local/lib/python3.6/site-packages/nautobot_capacity_metrics/api/views.py", line 26, in collect
    for metric in metric_jobs():
  File "/usr/local/lib/python3.6/site-packages/nautobot_capacity_metrics/metrics.py", line 79, in metric_jobs
    for job in job_results:
  File "/usr/local/lib/python3.6/site-packages/django/db/models/query.py", line 287, in __iter__
    self._fetch_all()
  File "/usr/local/lib/python3.6/site-packages/cacheops/query.py", line 273, in _fetch_all
    return self._no_monkey._fetch_all(self)
  File "/usr/local/lib/python3.6/site-packages/django/db/models/query.py", line 1308, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/usr/local/lib/python3.6/site-packages/django/db/models/query.py", line 53, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1143, in execute_sql
    sql, params = self.as_sql()
  File "/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 521, in as_sql
    distinct_params,
  File "/usr/local/lib/python3.6/site-packages/django/db/backends/base/operations.py", line 176, in distinct_sql
    raise NotSupportedError('DISTINCT ON fields is not supported by this database backend')

Steps to Reproduce

1. Use MySQL

[dgarros]

Looks like the issue is related specifically to the metric_jobs function
https://github.com/nautobot/nautobot-plugin-capacity-metrics/blob/cca347b62fe240afc6d98a069dfc86ba77acbcd8/nautobot_capacity_metrics/metrics.py#L65

As a workaround, it's recommended to disable both Jobs and gitrepositories in the plugin configuration when using MySQL until a proper fix has been implemented

PLUGINS_CONFIG = {
    "nautobot_capacity_metrics": {
        "app_metrics": {
            "gitrepositories": False,
            "jobs": False,
        }
    },