RelationService

In some cases, events may wish to reference other events. This could be to form a thread of messages for the user to follow along with, or to provide more context as to what a particular event is describing. Relation are used to associate new information with an existing event.

Relations are events which have an m.relates_to mixin in their contents, and the new information they convey is expressed in their usual event type and content.

Three types of relations are defined, each defining different behaviour when aggregated:

m.annotation - lets you define an event which annotates an existing event. When aggregated, groups events together based on key and returns a count. (aka SQL's COUNT) These are primarily intended for handling reactions.

m.replace - lets you define an event which replaces an existing event. When aggregated, returns the most recent replacement event. (aka SQL's MAX) These are primarily intended for handling edits.

m.reference - lets you define an event which references an existing event. When aggregated, currently doesn't do anything special, but in future could bundle chains of references (i.e. threads). These are primarily intended for handling replies (and in future threads).

m.thread - lets you define an event which is a thread reply to an existing event. When aggregated, returns the most thread event