Support query file

[hakobera]

BigqueryQuery task only support embedded query parameter. But sometimes we want to write long query which include parameters and load it from file.

So we extend BigqueryQuery task can accept query_file parameter.
query_file is ERB template file and can access attribute of task like:

SELECT
  id
FROM
  table
WHERE
  DATE(time) == <%= @today %>

task task1, type: bigquery_query do
  param :today, auto_bind: true, required: true
  param_set :query_file, 'path/to/query.sql'
end

[hakobera]

umm, I rethink specification, just use lambda is enough? So I move this issue's milestone to v0.3.0, and it is really needed or not.

Current BigqueryQuery support template query using string interpolation + hear document like this:

task task1, type: bigquery_query do
  param :today, auto_bind: true, required: true
  param_set :query, -> {
    >>-SQL
    SELECT
      id
    FROM
      table
    WHERE
      DATE(time) == '#{today}'
    SQL
  }
end

If you are using ruby 2.3+, you can use >>~ to remove leading indent.