def changeset(parent, params \ %{}) do
    parent
    |> cast(params, [:created_at , :parent_type , :mobile_number])
    |> unique_constraint(:mobile_number, name: :parents_mobile_number_uindex)

  end

** (exit) an exception was raised:
    ** (Ecto.ConstraintError) constraint error when attempting to update struct:

    * unique: parents_mobile_number_uindex

If you would like to convert this constraint into an error, please
call unique_constraint/3 in your changeset and define the proper
constraint name. The changeset has not defined any constraint.

        (ecto) lib/ecto/repo/schema.ex:493: anonymous fn/4 in Ecto.Repo.Schema.constraints_to_errors/3
        (elixir) lib/enum.ex:1229: Enum."-map/2-lists^map/1-0-"/2
        (ecto) lib/ecto/repo/schema.ex:479: Ecto.Repo.Schema.constraints_to_errors/3
        (ecto) lib/ecto/repo/schema.ex:284: anonymous fn/13 in Ecto.Repo.Schema.do_update/4
        (ecto) lib/ecto/repo/schema.ex:142: Ecto.Repo.Schema.update!/4
        (myapp) web/controllers/csvs_controller.ex:484: Myapp.CsvsController.parent_insert_or_update/2
        (myapp) web/controllers/csvs_controller.ex:266: anonymous fn/6 in Myapp.CsvsController.write_ecto_rows_schools/6
        (myapp) web/controllers/csvs_controller.ex:219: Myapp.CsvsController.write_ecto_rows_schools/6
        (elixir) lib/task/supervised.ex:85: Task.Supervised.do_apply/2
        (elixir) lib/task/supervised.ex:36: Task.Supervised.reply/5
        (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3