将属性传递为参数以使用LINQ / C＃创建过滤方法？

Question

Suppose I have these classes:

private class Model
{
    public DateTime FirstDate { get; set; }
    public DateTime SecondDate { get; set; }
    public DateTime FinalDate { get; set; }
    public string Name { get; set; }
}
private class Mommasan : Bandana
{
    public DateTime RestDate { get; set; }
    public DateTime TurboDate { get; set; }
    public string Name { get; set; }
}

All dates need to be filtered up to 3 days. So how can I create a generic filtering method for the DateTime properties? Using IQueryable ? I was hoping it would end up something like this:

(Obviously will not compile, but I'm guessing the idea)

void DoSpecificFilter<T>(ref IQueryable<T> query, DateTimeProperty property)
{
    DateTime today = today;
    query = query.Where(a => property <= today && today <= property.AddDays(3);
}

So if I need to filter Models who are on their final date, something like:

DoSpecificFilter<Model>(ref alreadyFilteredQuery, a => a.FinalDate);

and Mommasans who are on rest:

DoSpecificFilter<Mommasan>(ref alreadyFilteredQuery, a => a.RestDate);

Is this kind of thing possible at all or am I having the entirely wrong idea? Thanks!

Answer 1

You could work with DateTime -Selectors. For multiple DateTime fields you would have to chain them together. It would probably be easier to write an extention method for this:

public static class ExtentionMethods
{
    public static IQueryable<T> DoSpecificFilter<T>(
        this IQueryable<T> query, 
        Expression<Func<T, DateTime>> dateSelector, 
        DateTime filterValue, 
        bool blnTopLimit)
    {
        return query.Where(a => (blnTopLimit && dateSelector.Compile()(a) < filterValue)
            || (!blnTopLimit && dateSelector.Compile()(a) > filterValue));
    }
 }

Then you could use it like this:

 var query = queryableCollection
     .DoSpecificFilter((a) => a.RestDate, DateTime.Today, false)
     .DoSpecificFilter((a) => a.TurboDate, DateTime.Today, true);

Answer 2

Why not write an extension method on DateTime, and not look at the class at all? Something like ...

public static class Extensions
{
    public static IQueryable<T> DoSpecificFilter<T>(this DateTime value, IQueryable<T> query)
    {
        DateTime today = DateTime.Now;
        IQueryable<T> ret = query.Where(a => value <= today && today <= value.AddDays(3));
        return ret;
    }
}