Implement 'import' action

app/controllers/default/units_controller.rb

@@ -1,7 +1,8 @@
 class Default::UnitsController < ApplicationController
   navigation_tab :units
 
-  before_action :find_unit, only: [:import, :export, :destroy]
+  before_action -> { find_unit(current_user) }, only: :export
+  before_action -> { find_unit(nil) }, only: [:import, :destroy]
 
   before_action except: :index do
     case action_name.to_sym
@@ -17,9 +18,16 @@ class Default::UnitsController < ApplicationController
   end
 
   def import
+    current_user.units
+      .find_or_initialize_by(symbol: @unit.symbol)
+      .update!(base: @base, **@unit.slice(:name, :multiplier))
+    run_and_render :index
   end
 
   def import_all
+    # From defaults_diff return not only portability, but reason for not being
+    # portable: missing_base and nesting_too_deep. Add portable and
+    # missing_base, if possible in one query
   end
 
   def export
@@ -27,4 +35,11 @@ class Default::UnitsController < ApplicationController
 
   def destroy
   end
+
+  private
+
+  def find_unit(user)
+    @unit = Unit.find_by!(id: params[:id], user: user)
+    @base = Unit.find_by!(symbol: @unit.base.symbol, user: user? ? nil : user) if @unit.base
+  end
 end

app/models/unit.rb

@@ -28,9 +28,9 @@ class Unit < ApplicationRecord
           .outer_join(other_bases_units)
           .on(other_units[:base_id].eq(other_bases_units[:id]))
           .where(
-            other_bases_units[:symbol].eq(bases_units[:symbol])
+            other_bases_units[:symbol].is_not_distinct_from(bases_units[:symbol])
               .and(other_units[:symbol].eq(arel_table[:symbol]))
-              .and(other_units[:user_id].not_eq(arel_table[:user_id]))
+              .and(other_units[:user_id].is_distinct_from(arel_table[:user_id]))
           ).exists
       # Decide if Unit can be im-/exported based on existing hierarchy:
       # * same base unit symbol has to exist
@@ -43,14 +43,14 @@ class Unit < ApplicationRecord
               .join(sub_units).on(other_units[:id].eq(sub_units[:base_id]))
               .where(
                 other_units[:symbol].eq(arel_table[:symbol])
-                  .and(other_units[:user_id].not_eq(arel_table[:user_id]))
+                  .and(other_units[:user_id].is_distinct_from(arel_table[:user_id]))
               )
               .exists.not
           ).and(
             Arel::SelectManager.new.project(1).from(other_bases_units)
               .where(
-                other_bases_units[:symbol].eq(bases_units[:symbol])
-                  .and(other_bases_units[:user_id].not_eq(bases_units[:user_id]))
+                other_bases_units[:symbol].is_not_distinct_from(bases_units[:symbol])
+                  .and(other_bases_units[:user_id].is_distinct_from(bases_units[:user_id]))
               )
               .exists
           )

app/views/default/units/index.turbo_stream.erb

@@ -0,0 +1,3 @@
+<%= turbo_stream.update :units do %>
+  <%= render(@units) || render_no_items  %>
+<% end %>