fix: adding unique constraint for tag name

.gitignore

@@ -38,3 +38,4 @@ npm-debug.log
 yarn.lock
 MnesiaCore.nonode*
 Mnesia.nonode*
+.DS_Store

lib/tags_multi_tenant/tag.ex

@@ -3,14 +3,15 @@ defmodule TagsMultiTenant.Tag do
   import Ecto.Changeset
 
   schema "tags" do
-    field :name, :string
+    field(:name, :string)
 
-    has_many :taggings, TagsMultiTenant.Tagging
+    has_many(:taggings, TagsMultiTenant.Tagging)
   end
 
   def changeset(struct, params \\ %{}) do
     struct
     |> cast(params, [:name])
+    |> unique_constraint(:unique_tag_name, name: :tags_name_key)
     |> validate_required(:name)
   end
 end

priv/repo/migrations/20170602081401_update_tag_unique_index.exs

@@ -0,0 +1,9 @@
+defmodule TagsMultiTenant.Repo.Migrations.UpdateTagUniqueIndex do
+  use Ecto.Migration
+
+  def change do
+    drop_if_exists(unique_index(:tags, [:name], name: :tags_name_key))
+
+    create_if_not_exists(unique_index(:tags, [:name], name: :tags_name_key))
+  end
+end