Computed attributes

This information is still applicable to v6, for the code snippet, the CustomerActions class should be partial and the base type is not needed.

Computed attributes can be used as an alternative to views but still keep the same performance. By defining the expression for a computed attribute Vidyano can make sure that the expression is translated by Entity Framework to the correct sql code.

Usage

Computed attributes should be defined in the static Initialize method of the specific Persistent Objects’ Actions class and added manually as an attribute with the correct mapping. All computed attributes will automatically be flagged as read-only.

public class CustomerActions : PersistentObjectActionsReference<AdventureWorksEntityContainer, Customer>
{
    public static void Initialize()
    {
        SetComputedAttribute("OrdersCount", entity => entity.SalesOrderHeaders.Count);
        SetComputedAttribute("OrdersTotal", entity => entity.SalesOrderHeaders.Select(h => h.TotalDue).DefaultIfEmpty().Sum());
        SetComputedAttribute("FullName", entity => entity.FirstName + " " + entity.LastName);
    }

Once configured they can be used to sort, filter (with distincts) or group on. They can be shown in a query and when loading existing entities.

Remarks

Only valid EntityFramework expression can be used if the code needs to be translated to sql (e.g. no custom extension methods)