The upcasting of the XAF learning notes

Typically, we define an inheritance hierarchy, assuming there are types, customerbase,customertrialed,customerregistered three types, and the inheritance structure is as follows:

The business object code is defined as follows:

usingDevexpress.xpo; Public classCustomerbase:xpobject {stringFcustomername; Private stringFEMAIL;  PublicCustomerbase (Session session):Base(session) {} Public stringCustomerName {Get{returnFcustomername;} Set{setPropertyValue ("CustomerName",reffcustomername, value); }    }     Public stringEmail {Get{returnFEMAIL;} Set{setPropertyValue ("Email",refFEMAIL, value); }    }} Public classCustomerregistered:customerbase {stringfownedproducts;  PublicCustomerregistered (Session session):Base(session) {} Public stringownedproducts {Get{returnfownedproducts;} Set{setPropertyValue ("ownedproducts",reffownedproducts, value); }    }} Public classCustomertrialed:customerbase {stringftrialedproducts;  PublicCustomertrialed (Session session):Base(session) {} Public stringtrialedproducts {Get{returnftrialedproducts;} Set{setPropertyValue ("trialedproducts",refftrialedproducts, value); }    }}

We can use the following code to query all customer data.

New Xpcollection<customerbase> (Session1);

This collectionOfTypeIsCustomerbaseSoYouOnlyAccessCustomerbaseTypeOfProperty。NoCanAccessing the properties of a derived class，For example，OwnedproductsPropertyEvenCollection contains  customerregistered  object this Yes because base class type No know  ownedproducts  property

To break the limit , use the upcasting feature .

If you want to display the contents of a property, you canmodifies the xpbasecollection.displayableproperties property of the collection . set to this :"OID; CustomerName<customerregistered>ownedproducts ".

Over here，"Oid;CustomerName "IsPropertyValueOfPart <customerregistered>ownedproducts  is a property in a derived class

BuildQuery criteriaWhen，AlsoOKUseSameOfGrammar。For example, to all has buy or evaluation  xtragrid  customer , please using code

New Xpcollection<customerbase>(Session1, Criteriaoperator.parse ("<customerregistered >ownedproducts = ' Xtragrid ' or <customertrialed>trialedproducts = ' Xtragrid '  );

Use the following syntax to query a reference type property .

 Public classInvoice:xpobject {customerbase fcustomer;  PublicInvoice (Session session):Base(session) {}//This is a reference the Type property. It can reference any customerbase descendant.      Publiccustomerbase Customer {Get{returnFcustomer;} Set{setPropertyValue ("Customer",refFcustomer, value); }    }}//Uses upcasting to access customerregistered properties.Xpcollection<invoice> invoices =NewXpcollection<invoice>(Session1, Criteriaoperator.parse ("customer.<customerregistered>ownedproducts = ' Xtragrid '"));

As you can see, as long as you are a property in a derived class, you can use < to derive type > to convert, followed by the property name.

The upcasting of the XAF learning notes