Add database support and model for tips

db/migrate/20201007104221_create_tips.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class CreateTips < ActiveRecord::Migration[5.2]
+  def change
+    create_table :tips do |t|
+      t.string :title
+      t.text :description
+      t.text :example
+      t.references :file_type, foreign_key: true
+      t.references :user, polymorphic: true, null: false
+      t.timestamps
+    end
+
+    create_table :exercise_tips do |t|
+      t.references :exercise, null: false
+      t.references :tip, null: false
+      t.integer :rank, null: false
+      t.references :parent_exercise_tip, foreign_key: {to_table: :exercise_tips}
+      t.index %i[exercise_id tip_id rank], unique: true
+    end
+  end
+end