Uses length validation to hide add link when you reach maximum # of nested objects

lib/generators/nested_form/templates/jquery_nested_form.js

@@ -35,6 +35,7 @@ jQuery(function($) {
     content     = content.replace(regexp, "new_" + new_id);
 
     var field = $(content).insertBefore(this);
+    check_maximum();
     $(this).closest("form").trigger({type: 'nested:fieldAdded', field: field});
     return false;
   });
@@ -45,7 +46,18 @@ jQuery(function($) {
       hidden_field.value = '1';
     }
     $(this).closest('.fields').hide();
+    check_maximum();
     $(this).closest("form").trigger('nested:fieldRemoved');
     return false;
   });
+
+  function check_maximum() {
+    $('form a.add_nested_fields').each(function(){
+      var assoc   = $(this).attr('data-association');            // Name of child
+      var maximum = $(this).attr('data-maximum');                // Maximum # of children
+      $('.' + assoc+':visible').length >= maximum ? $(this).hide() : $(this).show();
+    });
+  }
+
+  check_maximum();
 });

lib/nested_form/builder.rb

@@ -16,6 +16,14 @@ def link_to_add(*args, &block)
       association = args.pop
       options[:class] = [options[:class], "add_nested_fields"].compact.join(" ")
       options["data-association"] = association
+      validators = self.object.class.validators_on(association)
+      unless validators.empty?
+        length_validator = validators.select {|item| item.class == ActiveModel::Validations::LengthValidator}.first
+        unless length_validator.nil?
+          maximum = length_validator.options[:maximum]
+          options["data-maximum"] = maximum
+        end
+      end
       args << (options.delete(:href) || "javascript:void(0)")
       args << options
       @fields ||= {}
@@ -57,7 +65,7 @@ def fields_for_with_nested_attributes(association_name, args, block)
     end
 
     def fields_for_nested_model(name, object, options, block)
-      output = '<div class="fields">'.html_safe
+      output = "<div class=\"fields #{object.class.name.underscore.pluralize}\">".html_safe
       output << super
       output.safe_concat('</div>')
       output