Filtering results in Phoenix using an exposed filters' form

index.html.eex

<h2>Listing policies</h2>

<form action="/policies" method="get">
  <%= select nil, :client_id, @clients, name: 'client_id' %>
  <input type="submit" value="Submit">
</form>

<%= pagination_links @page %>
  
<!-- HTML displaying the data rows -->

policy_controller.ex

..
def index(conn, _params) do
	page =
	Policy
	|> QueryFilter.filter(%Policy{}, _params, [:client_id])
	|> join(:left, [p], c in Client, p.client_id == c.id)
	|> where([p, c], c.user_id == ^conn.assigns.current_user.id)
	|> preload([p, c], [client: c])
	|> Repo.paginate(_params)

	render conn, :index,
	policies: page.entries,
	page_number: page.page_number,
	page_size: page.page_size,
	total_pages: page.total_pages,
	total_entries: page.total_entries,
	page: page,
end
..