Expression.Or - variable 'a' of type 'Appointment' referenced from scope '', but it is not defined

Question

I try to concate two expressions but get error mention in title on Compile method:

 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();

Additional two method to create Expressions:

 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;
    }

Any idea how to fix this error ? I am beginner with expression trees :/

are you sure you really need an expression tree? – Daniel A. White Apr 23 '14 at 12:21 — Daniel A. White, Apr 23 '14 at 12:21

score 3 · Accepted Answer · answered Apr 23 '14 at 12:23

3

week1 and week2 have different parameters, because they are created separately. The easiest way would be to use ExpressionInvoke on your existing expressions, with new ExpressionParameter instance:

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();

answered Apr 23 '14 at 12:23

MarcinJuraszek

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Thank You very much! I am confusing with this expressions and how it works :/ – netmajor Apr 23 '14 at 12:49

Expression.Or - variable 'a' of type 'Appointment' referenced from scope '', but it is not defined

1 Answers1