querylet

Querylet

Querylet is a templating language for SQL and is designed to make writing raw SQL much easier.

SELECT
  questions.id,
  questions.uuid,
  questions.question_html as question,
  questions.target_type as kind,
  {{#object}}
  SELECT
    case_study_questions.menu,
    case_study_questions.questions_pool_size,

    CASE {{str sub_question_type}}
    WHEN 'MultiChoiceQuestion' THEN
      {{> object 'questions.multiple_choice' id='{{sub_question_id}}' }} as question
    WHEN 'MultiSelectQuestion' THEN
      {{> object 'questions.multiple_select' id='{{sub_question_id}}' }} as question
    END,

    {{#array}}
      SELECT
        que.id,
        que.uuid,
        que.target_type as kind,
        choices.comment,
        choices.flagged,
        choices.choice_value as answered,
        multiple_select_questions.answers_count
      FROM ts_admin_que.questions que
      LEFT JOIN public.choices ON choices.question_id = que.id AND choices.attempt_id = {{id}}
      LEFT JOIN ts_admin_que.multiple_select_questions ON multiple_select_questions.id = que.target_id AND que.target_type = 'MultipleSelectQuestion'
      WHERE
        que.id = ANY(case_study_questions.question_ids)
    {{/array}} as questions
  {{/object}} as case_study
FROM ts_admin_que.questions
LEFT JOIN ts_admin_que.case_study_questions ON case_study_questions.question_id = questions.id
WHERE
  questions.id = {{id}}

Variable Filters

Int (Integer)

Cast variable to integer

{{int my_number}}

Str (String)

Cast variable to string

{{str my_string}}

Float

Cast variable to float

{{float my_number}}

Arr (Array)

Cast to array (not a postgres array)

{{arr my_array}}

Wild (Wildcard)

Wildcard front and back of string

{{wild my_string}}

Variables

{{my_variable}}

Partials

{{> include 'link.to.path' name='andrew' }}
{{> include 'link.to.path' name={{my_name}} }}
{{> include 'link.to.path' name={{str my_name}} }}

Partial blocks

{{#array}}
{{/array}}

If Else

{{#if variable}}
{{else}}
{{/end}}

Parslet

https://www.youtube.com/watch?time_continue=873&v=ET_POMJNWNs&feature=emb_title https://kschiess.github.io/parslet/parser.html https://www.rubydoc.info/github/kschiess/parslet/Parslet/Atoms/Scope

https://www.rubydoc.info/github/kschiess/parslet/Parslet/Atoms/Capture

Extra input after last repetition

https://stackoverflow.com/questions/27095141/how-do-i-get-my-parser-atom-to-terminate-inside-a-rule-including-optional-spaces

Parset Slice

str('Boston').parse('Boston') #=> "Boston"@0

The @0 is the offset

https://www.sitepoint.com/parsing-parslet-gem/

Parset Debugging

If the parser.rb runs into errors you can add the following to help debug what is happening

require 'parslet/convenience'
parser.parse_with_debug(input)

How it works:

• parser.rb — Create a grammar: What should be legal syntax?
• transform.rb — Annotate the grammar: What is important data?
• tree.rb - Create a transformation: How do I want to work with that data?

Parser

To see all the define rules check out parser_spec.rb

bundle exec rspec spec/parser_spec.rb

Transform

You capture patterns in your deep nested hash and the pass to a tree

Tree

The tree does something with your captured patterns