Question

I’m using LINQ to SQL for a .NET MVC app.

In my db i have a bunch of columns that have “Y” or “N” values in them.

I’m trying to write a general purpose method that will return all the records in the db where columnName == 'Y'

So far i’ve got this

public IQueryable<Approved> ReturnRecordsByObjectiveFlag(string columnName)
{       
    return from approved in db.Approved
           where approved.GetType().GetProperties().Where(x => x.Name.Equals(columnName)).Equals("Y")
           select approved;
}

But that gives me this error

Member access ‘System.String Name’ of ‘System.Reflection.MemberInfo’ not legal on type ‘System.Reflection.PropertyInfo[].

Any idea where i may be going wrong?

Thank you.

Answer 1

public IQueryable<Approved> ReturnRecordsByObjectiveFlag(string columnName)
{   
    var param = Expression.Parameter(typeof(Approved), "x");
    var predicate = Expression.Lambda<Func<Approved,bool>>(
        Expression.Equal(
            Expression.PropertyOrField(param, columnName),
            Expression.Constant("Y")
        ), param);
    return db.Approved.Where(predicate);
}

---

Edit; if the properties are actually char?, i.e. 'Y' not "Y", then:

public IQueryable<Approved> ReturnRecordsByObjectiveFlag(string columnName)
{
    var param = Expression.Parameter(typeof(Approved), "x");
    Expression prop;
    var predicate = Expression.Lambda<Func<Approved, bool>>(
        Expression.Equal(
            (prop = Expression.PropertyOrField(param, columnName)),
            Expression.Constant(prop.Type == typeof(string) ?
                (object)"Y" : (object)'Y', prop.Type)
        ), param);
    return db.Approved.Where(predicate);
}

(this now copes with all of string, char and char?