private AbsolutePageValues GetAbsolutePageValues()
{
var values = new AbsolutePageValues();
if (_pageInstruction == null)
{
values.PageSize = DEFAULT_PAGE_SIZE;
return(values);
}
values.PageSize = _pageInstruction.Size ?? DEFAULT_PAGE_SIZE;
values.AbsoluteOffset = 0;
values.EndOfPage = false;
if (_pageInstruction.PageNumber.HasValue)
{
if (_pageInstruction.PageNumber == 0)
{
throw new InvalidOperationException("There is no such thing as the 0th page.");
}
if (_pageInstruction.PageNumber < 0)
{
values.EndOfPage = true;
}
values.AbsoluteOffset += (Math.Abs(_pageInstruction.PageNumber.Value) - 1) * values.PageSize;
}
if (_pageInstruction.Offset.HasValue)
{
if (_pageInstruction.Offset < 0)
{
values.EndOfPage = true;
}
values.AbsoluteOffset += Math.Abs(_pageInstruction.Offset.Value);
}
return(values);
}
/// <summary>
/// Applies the offset and limit to the given queryable.
/// The number of items is limited to <see cref="PageSize"/>+1.
/// </summary>
public IQueryable <TItem> ApplyPagination(IQueryable <TItem> items)
{
AbsolutePageValues absolutePageValues = GetAbsolutePageValues();
if (absolutePageValues.EndOfPage)
{
items = items.Reverse();
}
if (absolutePageValues.AbsoluteOffset != 0)
{
items = items.Skip(absolutePageValues.AbsoluteOffset);
}
items = items.Take(absolutePageValues.PageSize + 1);
if (absolutePageValues.EndOfPage)
{
items = items.Reverse();
}
return(items);
}
