Document the use of Templating

What you expected to happen?

I attempted to use add templating to a dashboard, it is not documented how to use it so I provided these parameters: https://github.com/aknuds1/grafanalib/blob/master/grafanalib/core.py#L431-L439

        :param default: the default value for the variable
        :param dataSource: where to fetch the values for the variable from
        :param label: the variable's human label
        :param name: the variable's name
        :param query: the query users to fetch the valid values of the variable
        :param allValue: specify a custom all value with regex,
            globs or lucene syntax.
        :param includeAll: Add a special All option whose value includes
            all options.

What happened?

Js error in grafana when trying to import the resulting json dashboard. After some effort I determined that the js error is caued by the absence of some of these values for each template: https://github.com/aknuds1/grafanalib/blob/master/grafanalib/core.py#L456-L470

    def to_json_data(self):
        return {**_as_dict(self), **{
            'current': {
                'text': self.default,
                'value': self.default,
                'tags': [],
            },
            'hide': 0,
            'multi': False,
            'options': [],
            'refresh': 1,
            'regex': '',
            'sort': 1,
            'tagValuesQuery': None,
            'tagsQuery': None,
            'type': 'query',
        }}

I’m not very familiar with python but that bit of code looks like it should be used as defaults? In any case, when I include those keys/values for each templated variable in my dashboard.py, the resulting json generated does work!

How to reproduce it?

Create any dashboard that uses the templating, i.e.:

  templating=Templating(list=[
    { # namespace
      "default": "",
      "datasource": "prometheus",
      "label": "Namespace",
      "name": "namespace",
      "query": "label_values(kube_pod_info, namespace)",
      "allValue": ".+",
      "includeAll": True,
    },
  ]),

Is this a bug with how templating gets rendered? If not, can you add the proper incantation to use templating in the example dashboard.py?

[chrisfleming]

I’m still checking this out - but I think I’ve found the problem, in my experimentation, it looks like ‘selected’ has to be set to either True or False to get things working https://github.com/chrisfleming/grafanalib/commit/0589cb5e67084e9c63669514d3efa267b44cbcc4

I’ve a few more checks but should have a pull request next week.

[JamesGibo]

Could templating still be improved with some better docs? Or do we think this issue can be closed?