add docs

doc/db/README.md

@@ -0,0 +1,54 @@
+# Database
+
+Since the database stabilized quite well over the last months/years, hopefully it will not change that much in the future. 
+Thus, here is the current (October '24) model and the reasoning behind it:
+
+- **User**
+![](./user.svg)
+
+- All user-relevant fields are stored in `User`.
+- `Role` (and its associative table `UserRole`) map current roles the user has. This is used for e.g. permissions (`Vorstand`, `Admin`, `cox`, ... roles) and fee calculation (`Donau Linz`, `scheckbuch`, `Rennjugend`).
+- `Family` specifies, well, a family. Currently only used for fee calculation.
+
+- **Planned rowing adventures :-)**
+![](./planned.svg)
+
+There are 2 main types:
+    1. **Trips:** Trips can be created by every cox. They are "simple", every-day trips.
+    2. **Events:** Events can be created by everyone who has the `manage_events` role. They are used if multiple coxes are needed, e.g. for "Fetzenfahrt", "Anrudern", .... Additionally, events are shown in public calendar (e.g. on the website).
+
+`TripDetails` extracts the common data for both Trips and Events.
+Rower can register using the `UserTrip` table. 
+This table expects either...
+    - a `user_id`, if a person who has an account registers to the trip/event
+    - a `user_note`, if the cox of a trip, or a `manage_events` user of an event wants to add a guest which has no account
+
+- **Logbook**
+![](./logbook.svg)
+
+If `arrival` is NULL, the boat is assumed to still be on the water.
+There are a few `LogbookType`s:
+- `Wanderfahrt`: Used to check if a user has accomplished their `Fahrtenabzeichen` in the current year.
+- `Regatta`
+
+If the number of users entered is less than the boat's maximum capacity, the remaining spaces will be automatically assigned to guests.
+
+- **Boat**
+![](./boat.svg)
+
+- **Trailer**
+![](./trailer.svg)
+
+- **Fetching**
+![](./fetching.svg)
+
+This tables are used to automatically fetch data (every hour). Currently we have:
+- `Waterlevel` which fetches the current waterlevel in Linz from hydro (with their explicit permission :-))
+- `Weather` weather data from *Open Weather*
+
+- **Misc**
+![](./misc.svg)
+
+- **Log:** Logs "interesting" activities, to be viewed in the web ui
+- **Notification** 
+- **Distance:** Default distances of certain common targets