feat: use correct model for form

app/controllers/organisation_relationships_controller.rb

@@ -39,11 +39,11 @@ class OrganisationRelationshipsController < ApplicationController
 
   def create_housing_provider
     child_organisation = @organisation
-    if params[:organisation][:related_organisation_id].present?
+    if params[:organisation_relationship].present? && params[:organisation_relationship][:related_organisation_id].present?
       parent_organisation = related_organisation
     end
-    @resource = OrganisationRelationship.new(child_organisation:, parent_organisation:)
-    if @resource.save(context: :housing_provider)
+    @organisation_relationship = OrganisationRelationship.new(child_organisation:, parent_organisation:)
+    if @organisation_relationship.save(context: :housing_provider)
       flash[:notice] = "#{related_organisation.name} is now one of #{current_user.data_coordinator? ? 'your' : "this organisation's"} housing providers"
       redirect_to housing_providers_organisation_path
     else
@@ -54,11 +54,11 @@ class OrganisationRelationshipsController < ApplicationController
 
   def create_managing_agent
     parent_organisation = @organisation
-    if params[:organisation][:related_organisation_id].present?
+    if params[:organisation_relationship].present? && params[:organisation_relationship][:related_organisation_id].present?
       child_organisation = related_organisation
     end
-    @resource = OrganisationRelationship.new(child_organisation:, parent_organisation:)
-    if @resource.save(context: :managing_agent)
+    @organisation_relationship = OrganisationRelationship.new(child_organisation:, parent_organisation:)
+    if @organisation_relationship.save(context: :managing_agent)
       flash[:notice] = "#{related_organisation.name} is now one of #{current_user.data_coordinator? ? 'your' : "this organisation's"} managing agents"
       redirect_to managing_agents_organisation_path
     else
@@ -107,7 +107,7 @@ private
   end
 
   def related_organisation
-    @related_organisation ||= Organisation.find(params[:organisation][:related_organisation_id])
+    @related_organisation ||= Organisation.find(params[:organisation_relationship][:related_organisation_id])
   end
 
   def target_organisation

app/models/organisation_relationship.rb

@@ -1,7 +1,6 @@
 class OrganisationRelationship < ApplicationRecord
   belongs_to :child_organisation, class_name: "Organisation"
   belongs_to :parent_organisation, class_name: "Organisation"
-  validates :parent_organisation_id, uniqueness: { scope: [:child_organisation_id] }
   validate :validate_housing_provider_relationship, on: :housing_provider
   validate :validate_managing_agent_relationship, on: :managing_agent
 
@@ -9,20 +8,19 @@ private
 
   def validate_housing_provider_relationship
     if parent_organisation_id.blank?
-      child_organisation.errors.add :related_organisation_id, "You must choose a housing provider"
+      errors.add :related_organisation_id, "You must choose a housing provider"
     elsif OrganisationRelationship.exists?(child_organisation:, parent_organisation:)
-      child_organisation.errors.add :related_organisation_id, "You have already added this housing provider"
-    elsif !parent_organisation.holds_own_stock
-      errors.add :parent_organisation_id
-      child_organisation.errors.add :related_organisation_id, I18n.t("validations.scheme.owning_organisation.does_not_own_stock")
+      errors.add :related_organisation_id, "You have already added this housing provider"
+    elsif parent_organisation_id.present? && !parent_organisation.holds_own_stock
+      errors.add :related_organisation_id, I18n.t("validations.scheme.owning_organisation.does_not_own_stock")
     end
   end
 
   def validate_managing_agent_relationship
     if child_organisation_id.blank?
-      parent_organisation.errors.add :related_organisation_id, "You must choose a managing agent"
+      errors.add :related_organisation_id, "You must choose a managing agent"
     elsif OrganisationRelationship.exists?(child_organisation:, parent_organisation:)
-      parent_organisation.errors.add :related_organisation_id, "You have already added this managing agent"
+      errors.add :related_organisation_id, "You have already added this managing agent"
     end
   end
 end

app/views/organisation_relationships/add_housing_provider.html.erb

@@ -1,4 +1,4 @@
-<%= form_with model: @organisation, url: housing_providers_organisation_path, method: "post", local: true do |f| %>
+<%= form_with model: @organisation_relationship, url: housing_providers_organisation_path, method: "post", local: true do |f| %>
   <% if current_user.support? %>
     <%= render partial: "organisations/headings", locals: { main: @organisation.name, sub: nil } %>
     <%= render SubNavigationComponent.new(items: secondary_items(request.path, @organisation.id)) %>

app/views/organisation_relationships/add_managing_agent.html.erb

@@ -1,4 +1,4 @@
-<%= form_with model: @organisation, url: managing_agents_organisation_path, method: "post", local: true do |f| %>
+<%= form_with model: @organisation_relationship, url: managing_agents_organisation_path, method: "post", local: true do |f| %>
   <% if current_user.support? %>
     <%= render partial: "organisations/headings", locals: { main: @organisation.name, sub: nil } %>
     <%= render SubNavigationComponent.new(items: secondary_items(request.path, @organisation.id)) %>