Make Categories a predefined list

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

Allow null values for categories for now

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

priv/repo/migrations/20190222151449_drop_categories.exs

@@ -0,0 +1,35 @@
+defmodule Mobilizon.Repo.Migrations.DropCategories do
+  use Ecto.Migration
+
+  def up do
+    # The category field is a string for the time being
+    # while we determine the definitive minimal list of
+    # categories in https://framagit.org/framasoft/mobilizon/issues/30
+    # afterwards it will be a PostgreSQL enum and we'll
+    # just add new elements without being able to delete
+    # the previous ones
+    alter table(:events) do
+      add(:category, :string)
+      remove(:category_id)
+    end
+
+    drop(table(:categories))
+  end
+
+  def down do
+    create table(:categories) do
+      add(:title, :string)
+      add(:description, :string)
+      add(:picture, :string)
+
+      timestamps()
+    end
+
+    create(unique_index(:categories, [:title]))
+
+    alter table(:events) do
+      remove(:category)
+      add(:category_id, references(:categories, on_delete: :nothing))
+    end
+  end
+end