Document database migrations

Closes #390

CHANGELOG.rst

@@ -6,7 +6,10 @@ This document describes changes between each past release.
 3.1 (unreleased)
 ----------------
 
-- Nothing changed yet.
+Added
+=====
+
+- Document database migrations (#390)
 
 
 3.0 (2018-11-25)

Makefile

@@ -61,6 +61,11 @@ create-database-revision: ## Create a new database revision
 	@read -p "Please enter a message describing this revision: " rev_message; \
 	$(PYTHON) -m ihatemoney.manage db migrate -d ihatemoney/migrations -m "$${rev_message}"
 
+.PHONY: create-empty-database-revision
+create-empty-database-revision: ## Create an empty database revision
+	@read -p "Please enter a message describing this revision: " rev_message; \
+	$(PYTHON) -m ihatemoney.manage db revision -d ihatemoney/migrations -m "$${rev_message}"
+
 .PHONY: build-requirements
 build-requirements: ## Save currently installed packages to requirements.txt
 	$(VIRTUALENV) $(TEMPDIR)

docs/contributing.rst

@@ -39,7 +39,6 @@ Accessing dev server
 In any case, you can point your browser at `http://localhost:5000 <http://localhost:5000>`_.
 It's as simple as that!
 
-
 Updating
 --------
 
@@ -47,6 +46,22 @@ In case you want to update to newer versions (from git), you can just run the "u
 
   make update
 
+Create database migrations
+--------------------------
+
+In case you need to modify the database schema, first update the models in ihatemoney/models.py.
+Then run the following command to create a new database revision file::
+
+  make create-database-revision
+
+If your changes are simple enough, the generated script will be populated with
+the necessary migrations steps. You can edit the generated script. eg: to add data migrations.
+
+For complex migrations, it is recommended to start from an empty revision file which can be created
+with the following command::
+
+  make create-empty-database-revision
+
 Useful settings
 ----------------