Simplified Extension Example

db/field_extension.cds

@@ -0,0 +1,38 @@
+using {sap.capire.bookshop} from '_base/db/schema';
+using {sap.capire.orders} from '_base/db/schema';
+using from '_base/db/capire_common';
+
+using {
+  cuid,
+  managed,
+  Country,
+  sap.common.CodeList
+} from '@sap/cds/common';
+
+
+namespace Z_bookshop.fieldExtension;
+
+
+// extend existing entity
+extend orders.Orders with {
+  Z_orderInfo        : String default 'Webshop order';
+  Z_internalNo       : Integer; // uniqiue constraint
+  Z_expectedDelivery : Date; //mandatory
+  Z_priority         : String
+      @assert.range enum {
+      high;
+      medium;
+      low
+    } default 'medium';
+    Z_discount       : Decimal
+      @assert.range : [
+        0.0,
+        99.9
+      ] default 0.0;
+    }
+
+
+// new unique constraint (secondary index)
+annotate orders.Orders with @assert.unique : {Z_internalNo : [Z_internalNo]} {
+  Z_expectedDelivery @mandatory; // mandatory check
+}