有没有办法构建表达式< Func< T,bool>>来自表达式< Func< T>>？
比如上课
public class MyClass
{
public int Prop1{get;set;}
public int Prop2{get;set;}
public int Prop3{get;set;}
}
如果表达式< Func< T>>是()=>新的MyClass {Prop2 = 5}然后结果应该是x => x.Prop2 == 5
如果表达式< Func< T>>是()=>新的MyClass {Prop1 = 1,Prop3 = 3}然后结果应为x => x.Prop1 == 1&& x.Prop3 == 3
换句话说,是否可以在运行时创建具有任意数量条件的func？
解决方法
像这样：
static Expression<Func<T,bool>> Munge<T>(Expression<Func<T>> selector)
{
var memberInit = selector.Body as MemberInitExpression;
if (memberInit == null)
throw new InvalidOperationException("MemberInitExpression is expected");
var p = Expression.Parameter(typeof(T),"x");
Expression body = null;
foreach (MemberAssignment binding in memberInit.Bindings)
{
var comparer = Expression.Equal(
Expression.MakeMemberAccess(p,binding.Member),binding.Expression);
body = body == null ? comparer : Expression.AndAlso(body,comparer);
}
if (body == null) body = Expression.Constant(true);
return Expression.Lambda<Func<T,bool>>(body,p);
}
