Lessons

Lessons are presented to internal staff as a set of editable fields, which automatically generate a PDF guide according to a defined template when modified. Modifications made by admins are applied directly while modifications by writers require approval by an admin, at which point they’re automatically applied. Teachers and other school/organisation staff see lessons as a link to the guide and attached resources.

Though there are many lesson types, they’re all stored in a single lessons table and inherit from the base Lesson class using Rails’ built in single table inheritance. Shared behaviour like having attached resources and core validations are defined on the Lesson class, while more specific behaviour like type-specific enums and attributes for form generation are defined on the models for specific lesson types. Each lesson type for which a PDF guide is automatically generated includes the concern responsible for that type’s template (e.g. DailyActivity includes the DailyActivityPDF concern, which contains the logic for automatically generating DailyActivity guides.

Form Generation

Base lesson fields are provided by the lessons/_form partial. That partial uses the type of the lesson it’s passed to call another, type-specific partial which adds the type-specific fields. Those fields are added manually with the exception of listable and linkable fields, which can be generated automatically using their respective field partials.

Re-ordering the field names within the LISTABLE_ATTRIBUTES constant of a model will change the order they’re shown in on the form, and there is a content_for :priority_fields block available in the main form partial which allows fields to be inserted before the title field of the main form.

On a related note, you’ll notice I assign the return value of rendering the type-specific fields to a variable in the main form and render them by calling it later. This is necessary to ensure the :priority_fields within the type-specific partial are accessible by content_for, as otherwise they would not be evaluated until well after the content_for resolves.

Guide Generation

Handled by a collection of concerns found within app/models/concerns/pdfs. The base Lesson class includes the Pdfable concern which handles calling generate_guide on the type-specific model to generate a guide and attaching it to the lesson. It also prevents guide generation for lesson types which have a guide uploaded rather than generated.

PdfDefaults contains and sets up default values for values like font size, colors and fonts used in PDF generation. Pdfable includes it within the included block of the concern, which makes the defaults available to each type-specific concern as constants on the type-specific model.

The specifics of generating a guide for each lesson type are handled by the respective type-specific concerns (e.g. DailyActivityPDF for DailyActivity lessons). These concerns contain all the detailed logic related to adding and positioning images, text and bounding boxes on the page.

Guides are automatically generated on significant changes to a lesson through a controller callback calling the attach_guide provided by Pdfable. After generation, a job to generate a thumbnail of the PDF is queued and executed by SolidQueue when there are free resources.