Prevent setting null to not null foreign key

app/assets/javascripts/rails_admin/ra.filtering-multiselect.js

@@ -17,6 +17,7 @@
         return { query: query };
       },
       sortable: false,
+      removable: true,
       regional: {
         up: "Up",
         down: "Down",
@@ -78,24 +79,27 @@
 
 
       this.add = $('<a href="#" class="ui-icon ui-icon-circle-triangle-e ra-multiselect-item-add">' + this.options.regional.add + '</a>');
+      this.columns.center.append(this.add);
 
-      this.remove = $('<a href="#" class="ui-icon ui-icon-circle-triangle-w ra-multiselect-item-remove">' + this.options.regional.remove + '</a>');
+      if (this.options.removable) {
+        this.remove = $('<a href="#" class="ui-icon ui-icon-circle-triangle-w ra-multiselect-item-remove">' + this.options.regional.remove + '</a>');
+        this.columns.center.append(this.remove);
+      }
 
-      this.columns.center.append(this.add).append(this.remove)
       if (this.options.sortable) {
         this.up = $('<a href="#" class="ui-icon ui-icon-circle-triangle-n ra-multiselect-item-up">' + this.options.regional.up + '</a>');
         this.down = $('<a href="#" class="ui-icon ui-icon-circle-triangle-s ra-multiselect-item-down">' + this.options.regional.down + '</a>');
         this.columns.center.append(this.up).append(this.down);
       }
 
       this.selection = $('<select class="form-control ra-multiselect-selection" multiple="multiple"></select>');
+      this.columns.right.append(this.selection);
 
 
-
-      this.removeAll = $('<a href="#" class="ra-multiselect-item-remove-all"><span class="ui-icon ui-icon-circle-triangle-w"></span>' + this.options.regional.clearAll + '</a>');
-
-      this.columns.right.append(this.selection)
-                           .append(this.removeAll);
+      if (this.options.removable) {
+        this.removeAll = $('<a href="#" class="ra-multiselect-item-remove-all"><span class="ui-icon ui-icon-circle-triangle-w"></span>' + this.options.regional.clearAll + '</a>');
+        this.columns.right.append(this.removeAll);
+      }
 
       this.selection.wrap('<div class="wrapper"/>');
 
@@ -127,19 +131,21 @@
         widget.selection.trigger('change');
       });
 
-      /* Remove all from selection */
-      this.removeAll.click(function(e){
-        widget._deSelect($('option', widget.selection));
-        e.preventDefault();
-        widget.selection.trigger('change');
-      });
+      if (this.options.removable) {
+        /* Remove all from selection */
+        this.removeAll.click(function(e){
+          widget._deSelect($('option', widget.selection));
+          e.preventDefault();
+          widget.selection.trigger('change');
+        });
 
-      /* Remove from selection */
-      this.remove.click(function(e){
-        widget._deSelect($(':selected', widget.selection));
-        e.preventDefault();
-        widget.selection.trigger('change');
-      });
+        /* Remove from selection */
+        this.remove.click(function(e){
+          widget._deSelect($(':selected', widget.selection));
+          e.preventDefault();
+          widget.selection.trigger('change');
+        });
+      }
 
       var timeout = null;
       if(this.options.sortable) {

app/views/rails_admin/main/_form_filtering_multiselect.html.haml

@@ -26,6 +26,7 @@
     :'edit-url' => (authorized?(:edit, config.abstract_model) ? edit_path(model_name: config.abstract_model.to_param, id: '__ID__') : ''),
     remote_source: index_path(config.abstract_model, source_object_id: form.object.id, source_abstract_model: source_abstract_model.to_param, associated_collection: field.name, current_action: current_action, compact: true),
     sortable: !!field.orderable,
+    removable: !!field.removable,
     cacheAll: !!field.associated_collection_cache_all,
     regional: {
       chooseAll: t("admin.misc.chose_all"),

lib/rails_admin/config/fields/association.rb

@@ -57,6 +57,11 @@ def association # rubocop:disable TrivialAccessors
           @associated_collection_cache_all ||= (associated_model_config.abstract_model.count < 100)
         end
 
+        # Reader whether association's elements can be removed
+        def removable
+          association.foreign_key_nullable?
+        end
+
         # Reader for the association's child model's configuration
         def associated_model_config
           @associated_model_config ||= RailsAdmin.config(association.klass)

spec/integration/config/edit/rails_admin_config_edit_spec.rb

@@ -818,6 +818,44 @@ class HelpTest < Tableless
     end
   end
 
+  describe 'has_many', active_record: true do
+    context 'with not nullable foreign key' do
+      before do
+        RailsAdmin.config FieldTest do
+          edit do
+            field :nested_field_tests do
+              nested_form false
+            end
+          end
+        end
+        @field_test = FactoryGirl.create :field_test
+      end
+
+      it 'don\'t allow to remove element', js: true do
+        visit edit_path(model_name: 'FieldTest', id: @field_test.id)
+        is_expected.not_to have_selector('a.ra-multiselect-item-remove')
+        is_expected.not_to have_selector('a.ra-multiselect-item-remove-all')
+      end
+    end
+
+    context 'with nullable foreign key' do
+      before do
+        RailsAdmin.config Team do
+          edit do
+            field :players
+          end
+        end
+        @team = FactoryGirl.create :team
+      end
+
+      it 'allow to remove element', js: true do
+        visit edit_path(model_name: 'Team', id: @team.id)
+        is_expected.to have_selector('a.ra-multiselect-item-remove')
+        is_expected.to have_selector('a.ra-multiselect-item-remove-all')
+      end
+    end
+  end
+
   describe 'fields which are nullable and have AR validations', active_record: true do
     it 'is required' do
       # draft.notes is nullable and has no validation