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[Kristina Hoeppner <1522309@xxxxxxxxxxxxxxxxxx>]

** Changed in: mahara
    Milestone: 16.04.0 => 16.10.0

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https://bugs.launchpad.net/bugs/1522309

Title:
  Specify a strategy for representing inheritance/polymorphism in the
  database

Status in Mahara:
  Confirmed

Bug description:
  Mahara has a few prominent awkward database structures, that can be
  considered examples of polymorphism and/or inheritance, in the data
  structures we store in the database.

  Some of the awkward tables:

  1. The parallel tables for each plugintype: artefact_installed,
  blocktype_installed, etc; artefact_cron, blocktype_cron, etc...

  2. The multiple "owner" columns in the "view" table, which represent
  the different types of entities that can own a view (or collection, or
  artefact): view.owner, view.group, view.institution. This one has
  actually caused bugs so far, due to the need to make these columns
  nullable foreign keys, making it difficult to enforce the correct
  uniqueness constraint on some of the other columns.

  3. If we ever get around to implementing artefact permissions, and/or
  multiple collections per page, we'll have a similar situation with the
  "view_access" table.

  So far we've either copied Moodle or taken an ad-hoc "reinvent the
  wheel" approach to this issue. But there are actually a few known
  strategies for dealing with these situations, each of which has its
  own advantages and disadvantages. I think it would be good to
  summarize those into a table in the developer section of the wiki, so
  that we can make a more informed decision when implementing such
  tables in the future, or considering to refactor the existing tables.

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