Creating an OData Service with an Entity Relationship

Create an OData service called purchaseOrders.xsodata

service {
	"PO.Header"
	as "POHeader" navigates ("Items" as "POItem");

	"PO.Item"
	as "POItem";

	association "Items"
	principal "POHeader"("PURCHASEORDERID")
	multiplicity "1"
	dependent "POItem"("HEADER.PURCHASEORDERID")
	multiplicity "*";
}

And looks like this:

And if you see the error marker, you can safely ignore it. It is unfortunately a false error.

Run the core_xsjs module first, and then the web module. Replace the end of the URL to access the OData service and notice that the base service definition now has two entities.

The PO Header data now has a hyperlink relationship to the item entity.

Associations can be an excellent way to load child elements on demand; however there is also an option to expand the children details in place so that all levels can be retrieved with one request. Test the service again using the same steps as in the previous section of this exercise. This time add $expand=POItem to the end of the URL. You will then see that all the items are embedded within each header record (i.e., it is no longer deferred as in the previous test).