我尝试连接两个表达式,但在编译方法的标题中提到了错误:
Expression<Func<Appointment, bool>> week1 = StartDateIsBetween(lastMonday, nextSunday);
Expression<Func<Appointment, bool>> week2 = EndDateIsBetween(lastMonday, nextSunday);
BinaryExpression weekOr = Expression.Or(week1.Body, week2.Body);
Func<Appointment, bool> week = Expression.Lambda<Func<Appointment, bool>>(weekOr, week1.Parameters.Single()).Compile();
另外两种创建表达式的方法:
private Expression<Func<Appointment, bool>> StartDateIsBetween(DateTime beginningDate, DateTime endDate)
{
return a => a.StartDate >= beginningDate && a.StartDate <= endDate;
}
private Expression<Func<Appointment, bool>> EndDateIsBetween(DateTime beginningDate, DateTime endDate)
{
return a => a.EndDate >= beginningDate && a.EndDate <= endDate;
}
知道如何修复此错误吗?我是表达树的初学者:/
答案 0 :(得分:3)
week1
和week2
具有不同的参数,因为它们是单独创建的。最简单的方法是在现有表达式上使用ExpressionInvoke
,使用新的ExpressionParameter
实例:
var param = Expression.Parameter(typeof(Appointment));
var weekOr = Expression.Or(Expression.Invoke(week1, param), Expression.Invoke(week2, param));
var week = Expression.Lambda<Func<Appointment, bool>>(weekOr, param).Compile();