diff --git a/packages/forest_admin_datasource_mongoid/spec/lib/forest_admin_datasource_mongoid/utils/schema/field_flattener_spec.rb b/packages/forest_admin_datasource_mongoid/spec/lib/forest_admin_datasource_mongoid/utils/schema/field_flattener_spec.rb
new file mode 100644
index 00000000..97166ef4
--- /dev/null
+++ b/packages/forest_admin_datasource_mongoid/spec/lib/forest_admin_datasource_mongoid/utils/schema/field_flattener_spec.rb
@@ -0,0 +1,52 @@
+require 'spec_helper'
+
+module ForestAdminDatasourceMongoid
+  module Utils
+    module Schema
+      describe FieldsGenerator do
+        let(:stack) { [{ prefix: nil, as_fields: [], as_models: [] }] }
+
+        describe 'Construction' do
+          it 'does not modify the schema' do
+            fields = described_class.build_fields_schema(Post, stack)
+            expect(fields.keys).to eq(%w[_id created_at updated_at title body rating tag_ids])
+          end
+
+          it 'skips flattened models' do
+            stack = [{ prefix: nil, as_fields: ['section.body'], as_models: ['section'] }]
+            fields = described_class.build_fields_schema(Label, stack)
+
+            expect(fields.keys).to eq(['_id', 'name', 'section@@@body'])
+          end
+
+          it 'flattens all nested fields when no level is provided' do
+            stack = [{ prefix: nil, as_fields: ['section.content', 'section.body'], as_models: [] }]
+            fields = described_class.build_fields_schema(Label, stack)
+
+            expect(fields.keys).to eq(['_id', 'name', 'section@@@content', 'section@@@body'])
+          end
+
+          it 'flattens only requested fields' do
+            stack = [{ prefix: nil, as_fields: ['label.name'], as_models: [] }]
+            fields = described_class.build_fields_schema(Band, stack)
+
+            expect(fields.keys).to eq(['_id', 'created_at', 'updated_at', 'label', 'label@@@name'])
+          end
+
+          it 'onlies flatten selected fields when level = 1' do
+            stack = [{ prefix: nil, as_fields: ['label.name', 'label.section'], as_models: [] }]
+            fields = described_class.build_fields_schema(Band, stack)
+
+            expect(fields.keys).to eq(['_id', 'created_at', 'updated_at', 'label@@@name', 'label@@@section'])
+          end
+
+          it 'returns a "String" as type when "_id" is generated' do
+            fields = described_class.build_fields_schema(Post, stack)
+
+            expect(fields['_id'].column_type).to eq('String')
+          end
+        end
+      end
+    end
+  end
+end