"Persistent" query string and navigating the pages


On the index page I have a search box that user can use to type a filter query:

<form phx-change="search" class="search-form">
  <%= search_input :search_field, :query, placeholder: "Wyszukaj...", "phx-debounce": "300", value: @query %>

During typing, I’m generating phx-change (using debounce) that I handle in the event handler. That handler will generate updated assignments for the socket and the filtered view of the index page will be shown. And that works.
However, I need to somehow store the filter query string so it can be used also on the sub-pages too. Currently I’m storing the query string to the database (to given user’s row) and use it on sub-pages when I need.
And there comes the problem that I have: when user goes from sub-page to the index page (using browser back button or link provided on the sub-page [“back”]) the view of index is displayed as filter is not there (but it is there, since the input sets the value using: <%= search_input ...., "phx-debounce": "300", value: @query %>). So basically the phx-change event is not generated in that case.

How to overcome this? Maybe my architectural approach is incorrect in this context?

Well, OK I’ve fixed my problem by using the query in the mount function.

But I would like to hear from you, if this architectural approach is nice or not :wink:

I hope I understood your problem. The way I deal with this kind of issues is as follows:

  1. query string in URL changes → perform_search and update liveview

  2. phx-change event → issue a push_patch with a query string corresponding to the new search input. The push_patch updates the query string and triggers (1)

This way the state of your view, search input and query string in the URL are always in sync.

In (simplified) code:

# This handles (1)
def handle_params(params, _uri, socket) do
    search_input = params["search_field"] <-- This comes from the URL

        seach_results: peform_search(search_field)

# This handles (2)
def handle_event(
        %{"search_field" => search_field}, <-- This comes from the form input
      ) do

       to: Routes.api_path(socket, :your_live_view_page_name, search_field: search)

# This handles the initial mount
def mount(params, _session, socket) do

    {:noreply, socket} = handle_params(params, "", socket)


I hope this is what you were looking for.

1 Like

Hm…I understand your approach here but how in this, the “persistence” comes into play? I do want to use the filter on index live_view page but also on foo and bar sub-pages.

Could you elaborate a bit more on what you mean by “subpages” and how they relate to the index page? Is the search input field supposed to be visible on every page of your site?

You could generate all your links passing in a @global_query_params assign in your live link generators. Then in mount/handle_params have a helper that will retrieve, sanitize and set it.