Option select with reference - ruby-on-rails

Question

I have 2 Models: Unit and Emp
Also I have 2 controllers: Units and Emps
class CreateEmps < ActiveRecord::Migration[6.0]
def change
create_table :emps do |t|
t.string :name
t.references :unit
t.timestamps
end
end
end
class CreateUnits < ActiveRecord::Migration[6.0]
def change
create_table :units do |t|
t.string :name
t.timestamps
end
end
end
Looks simple.... but I guess too simple. I haven't found example how to do the following:
I need to have form for Emp creation.
So my question is .... how should it look like?
I want to have ComboBox with list of all objects in Units.
<%= form_with model: #emp do |f| %>
<p><%= f.label :name %>
<%= f.text_field :name %> </p>
<!-- What should go here? to ComboBox (option->select) -->
<%= f.submit "Create" %>
<% end %>
I am also confused how should it look like regargding emp_params for permiting.
EDIT:
class EmpsController < ApplicationController
def new
#emp = Emp.new
#unit_options = Unit.all.collect{|unit| [unit.name, unit.id] }
end
def create
#emp = Emp.new(emp_params)
#emp.save
redirect_to :action => :list
end
def destroy
#emp = Emp.find([:id])
#emp.destroy
redirect_to :action => :list
end
def list
#emps = Emp.all
end
def emp_params
params.require(:emp).permit(:name, :unit_id)
end
end

Answer 1

You want to use a select tag.
In your controller:
#unit_options = Unit.all.collect{|unit| [unit.name, unit.id] }
This creates a list of names and IDs, the order of each is name then value for the select option. You can of course scope or filter the results as needed.
In your view:
<%= form_with model: #emp do |f| %>
<div>
<%= f.label :name %>
<%= f.text_field :name %>
</div>
<div>
<%= f.label :unit_id, 'Unit' %>
<%= f.select :unit_id, #unit_options, {include_blank: true} %>
</div>
<%= f.submit "Create" %>
<% end %>
When used to edit the model, rails will select the option for the current value.