Migrations.md

+# Migrations
+When an application is already deployed and changes to the database are necessary, a migration needs to be written. This can be done as follows. If you have never written a migration before, obtain `h2-1.3.176.jar` and `liquibase.zip` from another developer. Then add liquibase to your path. When this is done, run the development branch with the following settings:
+```
+spring:
+    jpa:
+        hibernate:
+            ddl-auto: create
+    datasource:
+        url: jdbc:h2:file:./testdb-old;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE;DATABASE_TO_UPPER=false;
+        username: sa
+        password:
+```
+Then run your branch, but change `testdb-old` to `testdb-new`. Afterwards, you can generate a changelog with the following script:
+```
+PROJ_DIR=$1
+RESOURCES_DIR=$PROJ_DIR/src/main/resources
+
+liquibase \
+        --username=sa \
+        --password= \
+        --changeLogFile=$RESOURCES_DIR/changes.yaml \
+        --driver=org.h2.Driver \
+        --url=jdbc:h2:$PROJ_DIR/testdb-old \
+        --classpath=/usr/local/apps/h2/h2-1.3.176.jar \
+        --logLevel=info \
+            diffChangeLog \
+        --referenceUrl=jdbc:h2:$PROJ_DIR/testdb-new \
+        --referenceUsername=sa \
+        --referencePassword=
+```
+Finally, copy your changes from `changes.yaml` to the bottom of `migrations.yaml`. Double check whether the generated changelog makes sense. Sometimes, you might need to add default values or change column types.
+