private static CursorPageSlice <TEntity> PostProcessResultsIntoCursorPageSlice <TEntity>(
List <CursorResult <TEntity> > results,
SqlQuerySliceInfo sqlQuerySliceInfo,
int?totalCount
) where TEntity : class
{
bool hasPreviousPage = false;
bool hasNextPage = false;
if (sqlQuerySliceInfo.IsPreviousPagePossible)
{
var firstCursor = results.FirstOrDefault();
hasPreviousPage = firstCursor?.CursorIndex > 1; //Cursor Index is 1 Based; 0 would be the Cursor before the First
}
if (sqlQuerySliceInfo.IsNextPagePossible)
{
//GENERALLY This should Always Be True as we always increment the EndIndex if there is the Possibility that there might
// be a NEXT Page, and the ExpectedCount is always a value that should satisfy the processing
// (e.g. ExpectedCount might be int.MaxValue which would ensure our Take is always successful to get ALL Results).
if (sqlQuerySliceInfo.IsEndIndexOverFetchedForNextPageCheck && sqlQuerySliceInfo.ExpectedCount < int.MaxValue)
{
hasNextPage = results.Count > sqlQuerySliceInfo.ExpectedCount;
if (hasNextPage)
{
results.RemoveAt(results.Count - 1);
}
}
}
//Return a CursorPagedResult decorator for the results along with the Total Count!
var cursorPage = new CursorPageSlice <TEntity>(results, totalCount, hasPreviousPage, hasNextPage);
return(cursorPage);
}
/// <summary>
/// Helper method for converting Cursor Slice to OffsetPageResults for easier processing by calling code.
/// </summary>
/// <typeparam name="TEntity"></typeparam>
/// <param name="cursorPageSlice"></param>
/// <returns></returns>
public static OffsetPageResults <TEntity> ToOffsetPageResults <TEntity>(this CursorPageSlice <TEntity> cursorPageSlice)
//ALL entities retrieved and Mapped for Cursor Pagination must support IHaveCursor interface.
where TEntity : class
{
return(new OffsetPageResults <TEntity>(
cursorPageSlice.Results,
cursorPageSlice.HasNextPage,
cursorPageSlice.HasPreviousPage,
cursorPageSlice.TotalCount
));
}
public static ICursorPageSlice <T> SliceAsCursorPage <T>(this IEnumerable <T> items, string?after, int?first, string?before, int?last)
where T : class
{
//Do nothing if there are no results...
if (!items.Any())
{
return(new CursorPageSlice <T>(Enumerable.Empty <ICursorResult <T> >(), 0, false, false));
}
var afterIndex = after != null
? IndexEdge <string> .DeserializeCursor(after)
: 0;
var beforeIndex = before != null
? IndexEdge <string> .DeserializeCursor(before)
: 0;
//FIRST log the index of all items in the list BEFORE slicing, as these indexes are
// the Cursor Indexes for paging up/down the entire list, & ICursorResult is the Decorator
// around the Entity Models.
//NOTE: We MUST materialize this after applying index values to prevent ongoing increments...
int index = 0;
IEnumerable <ICursorResult <T> > slice = items
.Select(c => new CursorResult <T>(c, ++index))
.ToList();
int totalCount = slice.Count();
//If After specified, remove all before After (or skip past After)
if (afterIndex > 0 && slice.Last().CursorIndex > afterIndex)
{
slice = slice.Skip(afterIndex);
}
//If Before is specified, remove all after Before (Skip Until Before is reached)
if (beforeIndex > 0 && slice.Last().CursorIndex > beforeIndex)
{
slice = slice.SkipWhile(c => c.CursorIndex < beforeIndex);
}
//If First is specified, then take the first/top rows from the current Slice!
if (first.HasValue && first > 0 && slice.Count() > first)
{
slice = slice.Take(first.Value);
}
//If First is specified, then take the first/top rows from the current Slice!
if (last.HasValue && last > 0 && slice.Count() > last)
{
slice = slice.TakeLast(last.Value);
}
//Wrap all results into a PagedCursor Slice result wit Total Count...
//NOTE: to ensure our pagination is complete, we materialize the Results!
var results = slice.ToList();
var firstCursor = results.FirstOrDefault();
var lastCursor = results.LastOrDefault();
var cursorPageSlice = new CursorPageSlice <T>(
results,
totalCount,
hasPreviousPage: firstCursor?.CursorIndex > 1,
hasNextPage: lastCursor?.CursorIndex < totalCount
);
return(cursorPageSlice);
}
