Code duplication where impliment extension method for IEnumerable and IQueryable on entity set

Question

Since Entity Set does not support asqueryable, I have to do this. How can I reduce the amount of redundant code between the two methods?

public static IQueryable<T> WhereCreateWithin<T>(this IQueryable<T> query, DateManager.TimeRange timeRange, DateTime? beginDayParam = null) where T : IHasCreateDate
{
 if (beginDayParam == null)
 {
 beginDayParam = DateTime.Today;
 }
 DateTime beginDay = beginDayParam.Value.Date; 
 DateTime startRange;
 DateTime endRange;
 switch (timeRange)
 {
 case DateManager.TimeRange.All:
 return query;
 case DateManager.TimeRange.ThisYear:
 startRange = new DateTime(beginDay.Year, 1, 1); // January 1, this year
 endRange = startRange.AddYears(1);
 return query.Where(p => p.create_date.Date >= startRange && p.create_date < endRange);
 case DateManager.TimeRange.ThisMonth:
 startRange = new DateTime(beginDay.Year, beginDay.Month, 1);
 endRange = startRange.AddMonths(1).Date;
 return query.Where(p => p.create_date.Date >= startRange && p.create_date < endRange);
 case DateManager.TimeRange.ThisWeek:
 startRange = BuilkHelper.DateHelper.StartOfWeek(beginDay, DayOfWeek.Monday);
 endRange = startRange.AddDays(6);
 return query.Where(p => p.create_date.Date >= startRange && p.create_date < endRange);
 case DateManager.TimeRange.ToDay:
 return query.Where(p => p.create_date.Date == beginDay);
 case DateManager.TimeRange.Last30Day:
 startRange = beginDay.AddDays(-29);
 endRange = beginDay;
 return query.Where(p => p.create_date.Date >= startRange && p.create_date <= endRange);
 }
 return query;
}
public static IEnumerable<T> WhereCreateWithin<T>(this IEnumerable<T> query, DateManager.TimeRange timeRange, DateTime? beginDayParam = null) where T : IHasCreateDate
{
 if (beginDayParam == null)
 {
 beginDayParam = DateTime.Today;
 }
 DateTime beginDay = beginDayParam.Value.Date;
 DateTime startRange;
 DateTime endRange;
 switch (timeRange)
 {
 case DateManager.TimeRange.All:
 return query;
 case DateManager.TimeRange.ThisYear:
 startRange = new DateTime(beginDay.Year, 1, 1); // January 1, this year
 endRange = startRange.AddYears(1);
 return query.Where(p => p.create_date.Date >= startRange && p.create_date < endRange);
 case DateManager.TimeRange.ThisMonth:
 startRange = new DateTime(beginDay.Year, beginDay.Month, 1);
 endRange = startRange.AddMonths(1).Date;
 return query.Where(p => p.create_date.Date >= startRange && p.create_date < endRange);
 case DateManager.TimeRange.ThisWeek:
 startRange = BuilkHelper.DateHelper.StartOfWeek(beginDay, DayOfWeek.Monday);
 endRange = startRange.AddDays(6);
 return query.Where(p => p.create_date.Date >= startRange && p.create_date < endRange);
 case DateManager.TimeRange.ToDay:
 return query.Where(p => p.create_date.Date == beginDay);
 case DateManager.TimeRange.Last30Day:
 startRange = beginDay.AddDays(-29);
 endRange = beginDay;
 return query.Where(p => p.create_date.Date >= startRange && p.create_date <= endRange);
 }
 return query;
}

Answer 1

Given that the logic is exactly the same (i did not do a line by line comparision), one of the possible solutions whould be:

private static TCollection WhereCreateWithin<T, TCollection>(TCollection query,
 DateManager.TimeRange timeRange, 
 DateTime? beginDayParam,
 Func<TCollection, Func<T, bool>, TCollection> selector) 
 where T : IHasCreateDate
 where TCollection : IEnumerable<T>
{
 //insert your logic here
 //replace query.Where(x => ... ) call with selector(query, x => ... ) call
}
public static public static IQueryable<T> WhereCreateWithin<T>(this IQueryable<T> query, DateManager.TimeRange timeRange, DateTime? beginDayParam = null) where T : IHasCreateDate
{
 return WhereCreateWithin<T, IQueryable<T>>(query, timeRange, beginDayParam, (q, f) => q.Where(x => f(x)))
}
public static public static IEnumerable<T> WhereCreateWithin<T>(this IEnumerable<T> query, DateManager.TimeRange timeRange, DateTime? beginDayParam = null) where T : IHasCreateDate
{
 return WhereCreateWithin<T, IEnumerable<T>>(query, timeRange, beginDayParam, (q, f) => q.Where(f))
}

Answer 2

The IQueryable Where extension method takes an Expression whereas the IEnumerable Where extension method takes a normal delegate (Func). Any solution to consolidate the OPs code will have to take this into account. It is easy to convert an expression to a delegate by calling Compile on the expression (but hard the other way around) therefore I have based the below solution on the first principle.

public static IEnumerable<T> WhereCreateWithin<T>(this IEnumerable<T> query, DateManager.TimeRange timeRange, DateTime? beginDayParam = null) where T : IHasCreateDate
{
 return WhereCreateWithin<IEnumerable<T>, T>(query, timeRange, (q, ex) => q.Where(ex.Compile()), beginDayParam); 
}
public static IQueryable<T> WhereCreateWithin<T>(this IQueryable<T> query, DateManager.TimeRange timeRange, DateTime? beginDayParam = null) where T : IHasCreateDate
{
 return WhereCreateWithin<IQueryable<T>, T>(query, timeRange, (q, ex) => q.Where(ex), beginDayParam); 
}
public static TColl WhereCreateWithin<TColl, T>(this TColl toBeFiltered, 
 DateManager.TimeRange timeRange, 
 Func<TColl, Expression<Func<T, bool>>, TColl> getFilteredCollection, 
 DateTime? beginDayParam = null) where T : IHasCreateDate
 where TColl : IEnumerable<T>
{
 if (beginDayParam == null)
 {
 beginDayParam = DateTime.Today;
 }
 DateTime beginDay = beginDayParam.Value.Date;
 var expressionDictionary = new Dictionary<DateManager.TimeRange, Expression<Func<T, bool>>>();
 expressionDictionary.Add(DateManager.TimeRange.ThisYear, p => p.create_date.Date >= new DateTime(beginDay.Year, 1, 1) && p.create_date < new DateTime(beginDay.Year, 1, 1).AddYears(1));
 expressionDictionary.Add(DateManager.TimeRange.ThisMonth, p => p.create_date.Date >= new DateTime(beginDay.Year, beginDay.Month, 1) && p.create_date < new DateTime(beginDay.Year, beginDay.Month, 1).AddMonths(1).Date);
 expressionDictionary.Add(DateManager.TimeRange.ThisWeek, p => p.create_date.Date >= BuilkHelper.DateHelper.StartOfWeek(beginDay, DayOfWeek.Monday) && p.create_date < BuilkHelper.DateHelper.StartOfWeek(beginDay, DayOfWeek.Monday).AddDays(6));
 expressionDictionary.Add(DateManager.TimeRange.ToDay, p => p.create_date.Date == beginDay);
 expressionDictionary.Add(DateManager.TimeRange.Last30Day, p => p.create_date.Date >= beginDay.AddDays(-29) && p.create_date <= beginDay);
 return expressionDictionary.ContainsKey(timeRange) ? getFilteredCollection(toBeFiltered, expressionDictionary[timeRange]) : toBeFiltered;
}