history.queries

Overview

The queries behind the action-grouped history response.

A page is a page of actions, not of events, so grouping happens in the database before the paginator sees anything. That takes two reads: one for the page of groups, and one for the events belonging to those groups. Neither grows with the number of events on the page.

Both reads run over the same union. Its parts are pghistory's events that reference the object, which are the object's own events and the events of rows with a foreign key to it, and the object's workflow state events.

action_groups_for

One row per action, newest first, ready to paginate.

state_events names the object's workflow state events, as :func:vueda.history.sources.state_events_for returns them.

Django cannot group a union, so the union runs as a common table expression and the grouping selects from it. Each part selects only the columns that grouping reads. That lets the database skip building every event's data and difference, which is most of the cost of a long history.

Actions that share a recorded time break the tie on their earliest event's identifier parts, the tracked model label and then the numeric event id, which is the published rule. That keeps a page boundary in the same place between requests without comparing identifiers as strings, where :9 would sort after :10.

Signature

action_groups_for(instance, user, state_events)

Parameters

Name	Type	Required	Default	Description
instance		yes
user		yes
state_events		yes

Source

server/vueda/history/queries.py:89

events_in_groups

Every visible event of the named groups, in the order they were written.

Each part is narrowed to the named groups before the union, so the database builds the data and difference of the page's events only. Each event carries the moment of its own write, so the recorded time orders a group faithfully. The tracked model label and the event id break a tie, which keeps a rendered group from reshuffling between requests. Each event is annotated with its group_key and its published relation.

Signature

events_in_groups(instance, user, state_events, group_keys)

Parameters

Name	Type	Required	Default	Description
instance		yes
user		yes
state_events		yes
group_keys		yes

Source

server/vueda/history/queries.py:119

Source

server/vueda/history/queries.py