/// <summary>
/// Applies the cursor pagination algorithm to the <paramref name="query"/>.
/// </summary>
/// <param name="query">
/// The query on which the the cursor pagination algorithm shall be applied to.
/// </param>
/// <param name="context">
/// The field resolver context.
/// </param>
/// <param name="defaultPageSize">
/// The default page size if no boundaries are set.
/// </param>
/// <param name="totalCount">
/// The total count if already known.
/// </param>
/// <param name="cancellationToken">
/// The cancellation token.
/// </param>
/// <typeparam name="TEntity">
/// The entity type.
/// </typeparam>
/// <returns>
/// Returns a connection instance that represents the result of applying the
/// cursor paging algorithm to the provided <paramref name="query"/>.
/// </returns>
public static ValueTask <Connection <TEntity> > ApplyCursorPaginationAsync <TEntity>(
this IQueryable <TEntity> query,
IResolverContext context,
int?defaultPageSize = null,
int?totalCount = null,
CancellationToken cancellationToken = default)
{
if (query is null)
{
throw new ArgumentNullException(nameof(query));
}
if (context is null)
{
throw new ArgumentNullException(nameof(context));
}
var first = context.ArgumentValue <int?>(CursorPagingArgumentNames.First);
var last = context.ArgumentValue <int?>(CursorPagingArgumentNames.Last);
if (first is null && last is null)
{
first = defaultPageSize;
}
var arguments = new CursorPagingArguments(
first,
last,
context.ArgumentValue <string?>(CursorPagingArgumentNames.After),
context.ArgumentValue <string?>(CursorPagingArgumentNames.Before));
return(QueryableCursorPagination <TEntity> .Instance.ApplyPaginationAsync(
query,
arguments,
totalCount,
cancellationToken));
}
async ValueTask <IPage> IPagingHandler.SliceAsync(
IResolverContext context,
object source)
{
var first = context.ArgumentValue <int?>(CursorPagingArgumentNames.First);
var last = AllowBackwardPagination
? context.ArgumentValue <int?>(CursorPagingArgumentNames.Last)
: null;
if (first is null && last is null)
{
first = DefaultPageSize;
}
var arguments = new CursorPagingArguments(
first,
last,
context.ArgumentValue <string?>(CursorPagingArgumentNames.After),
AllowBackwardPagination
? context.ArgumentValue <string?>(CursorPagingArgumentNames.Before)
: null);
return(await SliceAsync(context, source, arguments).ConfigureAwait(false));
}
/// <summary>
/// Applies the pagination algorithm to the provided query.
/// </summary>
/// <param name="query">The query builder.</param>
/// <param name="arguments">The paging arguments.</param>
/// <param name="totalCount">Specify the total amount of elements</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns>
/// Returns the connection.
/// </returns>
public async ValueTask <Connection <TEntity> > ApplyPaginationAsync(
TQuery query,
CursorPagingArguments arguments,
int?totalCount,
CancellationToken cancellationToken)
{
if (query is null)
{
throw new ArgumentNullException(nameof(query));
}
var maxElementCount = int.MaxValue;
Func <CancellationToken, ValueTask <int> > executeCount = totalCount is null ?
ct => CountAsync(query, ct)
: _ => new ValueTask <int>(totalCount.Value);
// We only need the maximal element count if no `before` counter is set and no `first`
// argument is provided.
if (arguments.Before is null && arguments.First is null)
{
var count = await executeCount(cancellationToken);
maxElementCount = count;
// in case we already know the total count, we override the countAsync parameter
// so that we do not have to fetch the count twice
executeCount = _ => new ValueTask <int>(count);
}
CursorPagingRange range = SliceRange(arguments, maxElementCount);
var skip = range.Start;
var take = range.Count();
// we fetch one element more than we requested
if (take != maxElementCount)
{
take++;
}
TQuery slicedSource = query;
if (skip != 0)
{
slicedSource = ApplySkip(query, skip);
}
if (take != maxElementCount)
{
slicedSource = ApplyTake(slicedSource, take);
}
IReadOnlyList <Edge <TEntity> > selectedEdges =
await ExecuteAsync(slicedSource, skip, cancellationToken);
var moreItemsReturnedThanRequested = selectedEdges.Count > range.Count();
var isSequenceFromStart = range.Start == 0;
selectedEdges = new SkipLastCollection <Edge <TEntity> >(
selectedEdges,
moreItemsReturnedThanRequested);
ConnectionPageInfo pageInfo =
CreatePageInfo(isSequenceFromStart, moreItemsReturnedThanRequested, selectedEdges);
return(new Connection <TEntity>(selectedEdges, pageInfo, executeCount));
}
/// <summary>
/// Applies the pagination algorithm to the provided query.
/// </summary>
/// <param name="query">The query builder.</param>
/// <param name="arguments">The paging arguments.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns>
/// Returns the connection.
/// </returns>
public ValueTask <Connection <TEntity> > ApplyPaginationAsync(
TQuery query,
CursorPagingArguments arguments,
CancellationToken cancellationToken) =>
ApplyPaginationAsync(query, arguments, null, cancellationToken);
protected override ValueTask <Connection> SliceAsync(IResolverContext context, object source, CursorPagingArguments arguments)
{
//If Appropriate we handle the values here to ensure that no post-processing is done other than
// correctly mapping the results into a GraphQL Connection as Edges with Cursors...
if (source is IPreProcessedCursorSlice <TEntity> pagedResults)
{
bool includeTotalCountEnabled = this.PagingOptions.IncludeTotalCount ?? PagingDefaults.IncludeTotalCount;
var graphQLParamsContext = new GraphQLParamsContext(context);
//Optimized to only require TotalCount value if the query actually requested it!
if (includeTotalCountEnabled && graphQLParamsContext.IsTotalCountRequested && pagedResults.TotalCount == null)
{
throw new InvalidOperationException($"Total Count is requested in the query, but was not provided with the results [{this.GetType().GetTypeName()}] from the resolvers pre-processing logic; TotalCount is null.");
}
int?totalCount = pagedResults.TotalCount;
//Ensure we are null safe and return a valid empty list by default.
IReadOnlyList <IndexEdge <TEntity> > selectedEdges =
pagedResults?.ToEdgeResults().ToList() ?? new List <IndexEdge <TEntity> >();;
IndexEdge <TEntity>?firstEdge = selectedEdges.FirstOrDefault();
IndexEdge <TEntity>?lastEdge = selectedEdges.LastOrDefault();
var connectionPageInfo = new ConnectionPageInfo(
hasNextPage: pagedResults?.HasNextPage ?? false,
hasPreviousPage: pagedResults?.HasPreviousPage ?? false,
startCursor: firstEdge?.Cursor,
endCursor: lastEdge?.Cursor,
totalCount: totalCount ?? 0
);
var graphQLConnection = new Connection <TEntity>(
selectedEdges,
connectionPageInfo,
ct => new ValueTask <int>(connectionPageInfo.TotalCount ?? 0)
);
return(new ValueTask <Connection>(graphQLConnection));
}
throw new GraphQLException($"[{nameof(PreProcessedCursorPagingHandler<TEntity>)}] cannot handle the specified data source of type [{source.GetType().Name}].");
}
public static ICursorPageSlice <T> SliceAsCursorPage <T>(this IEnumerable <T> items, CursorPagingArguments graphQLPagingArgs)
where T : class
{
return(items.SliceAsCursorPage(
after: graphQLPagingArgs.After,
first: graphQLPagingArgs.First,
before: graphQLPagingArgs.Before,
last: graphQLPagingArgs.Last
));
}
protected abstract ValueTask <Connection> SliceAsync(
IResolverContext context,
object source,
CursorPagingArguments arguments);