Add a warning about missing ordering key fields for data events

Internal ticket #552

Closes #134

client/Pages/EventTypeCreate/View.elm

@@ -315,6 +315,24 @@ viewForm model setup =
                 Help.orderingKeyFields
                 Optional
                 Enabled
+            , if getValue FieldCategory formModel.values == categories.data
+                  && ( getValue FieldOrderingKeyFields formModel.values
+                     |> String.trim
+                     |> String.isEmpty ) then
+                div [ class "dc-msg dc-msg--error" ]
+                  [ h3 [ class "blinking" ] [ text "Warning!" ]
+                  , p [ class "dc-p" ]
+                      [ text "The 'ordering key' information defines the transactional"
+                      , text " business order that finally leads to the event creation, and"
+                      , text " is used e.g. for analytics change data capture, i.e. keeping"
+                      , text " transactional data in sync as source for analytics. The"
+                      , text " information is recommended for (external) data change events"
+                      , text " -- see "
+                      , externalLink "API/Event Guidelines" "https://opensource.zalando.com/restful-api-guidelines/#203"
+                      , text "." ]
+                  ]
+              else
+                none
             , selectInput formModel
                 FieldAudience
                 OnInput