Form tag without controller

Generally you will start with an empty changeset for your schema, saving it into the socket assigns in mount/3:

def mount(_, _, socket) do
  changeset = User.changeset(%User{})

  {:ok, assign(socket, changeset: changeset)}
end

Then you can use the .form helper with that changeset (in the .html.heex):

<.form let={f} for={@changeset} phx_submit="action_name">
  <%= text_input f, :name %>
  <%= text_input f, :address %>
  <%= text_input f, :any_other_field_in_the_schema %>

  <%= submit "Submit Button Text Here" %>
</.form>

The f represents the form itself, and will be passed as the first argument to your inputs. The "action_name" will be used by the event handler in your LiveView:

def handle_event("action_name", %{"user" => params}, socket) do
  case Accounts.register_user(params) do
      {:ok, user} ->
        ...
        {:noreply, socket}

      {:error, %Ecto.Changeset{} = changeset} ->
        {:noreply, assign(socket, changeset: changeset)}
    end
end

The second argument %{"user" => params} is the form data (as strings) e.g.

%{
  "user" => %{
    "name" => "test name",
    "address" => "123 Fake St",
    "any_other_field_in_the_schema" => "sample"
  }
}

Docs for reference: Phoenix.HTML.Form — Phoenix.HTML v4.3.0

And if you want labels or error messages attached to a field, you can use helpers for that too:

<%= label f, :name %>
<%= text_input f, :name %>
<%= error_tag f, :name %>

The error_tag will display any errors from the changeset when the user enters invalid data.

If you want the errors to display “live” (before the submit button is pressed), you can use live validation like

<.form let={f} for={@changeset} phx_submit="action_name" phx_change="validate">

Where "validate" goes to another event handler which updates the changeset:

def handle_event("validate", %{"user" => params}, socket) do
  changeset =
    %User{}
    |> User.changeset(params)
    |> Map.put(:action, :insert)

  {:noreply, assign(socket, changeset: changeset)}
end

Thanx for the reply ,but i am still stuck

def mount(%{“rid” => roomid}, _session, socket) do
{:ok, assign(socket, room: roomid)}
end

I have room ID which i also had to pass to html.heex

for ref :https://www.youtube.com/watch?v=fyg0FuSL5DY

I am using this video to create a live view chat application ,if possible please see this video from 27 min onward

import Phoenix.LiveView.Helpers

Welcome to Phoenix Room => <%= @room %>

<.form let={f} for={@changeset} phx_submit=“action_name”>
<%= text_input f, :Message %>

<%= submit “Submit Button Text Here” %>
</.form>