sabine/persistent-history

(experimental) TH functions to generate revision history models for a persistent schema

Don't use this, since this is an experimental "library" written by a Template Haskell newbie. If you do nonetheless, know that you have been warned.

This is far from complete, and will probably grow if I find the time to pursue the projects I use this in. If you are interested in contributing, please get in touch by opening an issue.

TODO:

• go through https://wiki.haskell.org/How_to_write_a_Haskell_program and write documentation
• ask for a code review

What is this and how does it work?

I wanted to have a way to record the history of previous revisions of the records in my database. Similar to persistent-audit (https://github.com/plow-technologies/persistent-audit), what I do here is based on http://www.4guysfromrolla.com/webtech/041807-1.shtml, i.e. there is a separate history table for every table.

Currently, there are

• types Created, Updated, Deleted that record the UTCTime at which the record was updated, or, respectively, a Boolean that says whether the record is deleted.
• a function addHistoryDefs that transforms the entity definition list from persistent by
  • adding a history model for every model that is annotated with the attribute history, and
  • adding the created, createdBy, updated, updatedBy, and deleted fields to the annotated model
• a TH function mkHistory that creates insert, insertKey, select, selectFirst, update, and delete functions for the model with history