Expression.Or - 从范围''引用的'约会'类型的变量'a'，但它没有定义

Question

我尝试连接两个表达式，但在编译方法的标题中提到错误：

 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：/

Answer 1

week1和week2有不同的参数，因为它们是单独创建。 最简单的方法是使用新的ExpressionParameter实例在现有表达式上使用ExpressionInvoke ：

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();