Evaluate用法

1.语法

public object Evaluate( 
   Type objectType,  
   CriteriaOperator expression,  
   CriteriaOperator criteria 
);

Parameters

objectType

        A System.Type object that identifies the type of objects against which the expression will be evaluated.

expression

A DevExpress.Data.Filtering.CriteriaOperator object that specifies the expression to evaluate.

criteria

A DevExpress.Data.Filtering.CriteriaOperator object that specifies the filter criteria. The objects that match this criteria will be used to evaluate the expression.

Return Value

The value evaluated.

2.用法

      <1>
      

using DevExpress.Xpo;
using DevExpress.Data.Filtering;

// A custom XPobject
class Person : XPObject {
   //...
   bool isMale;
   public bool IsMale {
      get { return isMale; }
      set { isMale = value; }
   }      
}

// Calculate the number of objects.
object count = Session.DefaultSession.Evaluate(typeof(Person), CriteriaOperator.Parse("Count()"), 
    CriteriaOperator.Parse("IsMale = true"))

　　　　<2>

　　　　

using DevExpress.Data.Filtering;

//...

decimal sumPaid = (decimal)session.Evaluate<Order>(CriteriaOperator.Parse("Sum(OrderTotals)"), 
    new BinaryOperator("OrderDate", DateTime.Today.AddDays(-10), BinaryOperatorType.Greater));