async ValueTask <IPage> IPagingHandler.SliceAsync(
IResolverContext context,
object source)
{
int?skip = context.ArgumentValue <int?>(OffsetPagingArgumentNames.Skip);
int?take = context.ArgumentValue <int?>(OffsetPagingArgumentNames.Take);
var arguments = new OffsetPagingArguments(skip, take ?? DefaultPageSize);
return(await SliceAsync(context, source, arguments).ConfigureAwait(false));
}
protected override ValueTask <CollectionSegment> SliceAsync(
IResolverContext context,
object source,
OffsetPagingArguments arguments)
{
return(source switch
{
IQueryable <TItemType> q => ResolveAsync(context, q, arguments),
IEnumerable <TItemType> e => ResolveAsync(context, e.AsQueryable(), arguments),
IExecutable <TItemType> ex => SliceAsync(context, ex.Source, arguments),
_ => throw new GraphQLException("Cannot handle the specified data source.")
});
protected override async ValueTask <CollectionSegment> SliceAsync(
IResolverContext context,
object source,
OffsetPagingArguments arguments)
{
IQueryable <TItemType> queryable = source switch
{
IQueryable <TItemType> q => q,
IEnumerable <TItemType> e => e.AsQueryable(),
_ => throw new GraphQLException("Cannot handle the specified data source.")
};
IQueryable <TItemType> original = queryable;
if (arguments.Skip.HasValue)
{
queryable = queryable.Skip(arguments.Skip.Value);
}
queryable = queryable.Take(arguments.Take + 1);
List <TItemType> items =
await ExecuteQueryableAsync(queryable, context.RequestAborted)
.ConfigureAwait(false);
var pageInfo = new CollectionSegmentInfo(
items.Count == arguments.Take + 1,
(arguments.Skip ?? 0) > 0);
if (items.Count > arguments.Take)
{
items.RemoveAt(arguments.Take);
}
return(new CollectionSegment((IReadOnlyCollection <object>)items, pageInfo, CountAsync));
async ValueTask <int> CountAsync(CancellationToken cancellationToken) =>
await Task.Run(original.Count, cancellationToken).ConfigureAwait(false);
}
/// <summary>
/// Applies the pagination algorithm to the provided data.
/// </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>
public async ValueTask <CollectionSegment <TEntity> > ApplyPaginationAsync(
TQuery query,
OffsetPagingArguments arguments,
int?totalCount,
CancellationToken cancellationToken)
{
Func <CancellationToken, ValueTask <int> > getTotalCount = totalCount is null
? async ct => await CountAsync(query, ct)
: _ => new ValueTask <int>(totalCount.Value);
TQuery sliced = query;
if (arguments.Skip is { } skip)
{
sliced = ApplySkip(sliced, skip);
}
if (arguments.Take is { } take)
{
sliced = ApplyTake(sliced, take + 1);
}
IReadOnlyList <TEntity> items =
await ExecuteAsync(sliced, cancellationToken).ConfigureAwait(false);
bool hasNextPage = items.Count == arguments.Take + 1;
bool hasPreviousPage = (arguments.Skip ?? 0) > 0;
CollectionSegmentInfo pageInfo = new(hasNextPage, hasPreviousPage);
items = new SkipLastCollection <TEntity>(items, skipLast: hasNextPage);
return(new CollectionSegment <TEntity>(
items,
pageInfo,
getTotalCount));
}
protected override async ValueTask <CollectionSegment> SliceAsync(
IResolverContext context,
object source,
OffsetPagingArguments arguments)
{
IQueryable <TItemType> queryable = source switch
{
IQueryable <TItemType> q => q,
IEnumerable <TItemType> e => e.AsQueryable(),
_ => throw new GraphQLException("Cannot handle the specified data source.")
};
IQueryable <TItemType> original = queryable;
if (arguments.Skip.HasValue)
{
queryable = queryable.Skip(arguments.Skip.Value);
}
queryable = queryable.Take(arguments.Take + 1);
List <TItemType> items =
await ExecuteQueryableAsync(queryable, context.RequestAborted)
.ConfigureAwait(false);
var pageInfo = new CollectionSegmentInfo(
items.Count == arguments.Take + 1,
(arguments.Skip ?? 0) > 0);
if (items.Count > arguments.Take)
{
items.RemoveAt(arguments.Take);
}
Func <CancellationToken, ValueTask <int> > getTotalCount =
ct => throw new InvalidOperationException();
// TotalCount is one of the heaviest operations. It is only necessary to load totalCount
// when it is enabled (IncludeTotalCount) and when it is contained in the selection set.
if (IncludeTotalCount &&
context.Field.Type is ObjectType objectType &&
context.FieldSelection.SelectionSet is {} selectionSet)
{
IReadOnlyList <IFieldSelection> selections = context
.GetSelections(objectType, selectionSet, true);
var includeTotalCount = false;
for (var i = 0; i < selections.Count; i++)
{
if (selections[i].Field.Name.Value is "totalCount")
{
includeTotalCount = true;
break;
}
}
// When totalCount is included in the selection set we prefetch it, then capture the
// count in a variable, to pass it into the clojure
if (includeTotalCount)
{
var captureCount = original.Count();
getTotalCount = ct => new ValueTask <int>(captureCount);
}
}
return(new CollectionSegment(
(IReadOnlyCollection <object>)items,
pageInfo,
getTotalCount));
}
/// <summary>
/// The algorithm defining how to slice data of the specified <paramref name="source"/>.
/// </summary>
/// <param name="context">
/// The resolver context of the execution field.
/// </param>
/// <param name="source">
/// The object representing the data source, collection, or query builder.
/// </param>
/// <param name="arguments">
/// The paging arguments provided by the user.
/// </param>
/// <returns>
/// The <see cref="CollectionSegment"/> representing
/// the slice of items belonging to the requested page.
/// </returns>
protected abstract ValueTask <CollectionSegment> SliceAsync(
IResolverContext context,
object source,
OffsetPagingArguments arguments);
/// <summary>
/// Applies the pagination algorithm to the provided data.
/// </summary>
/// <param name="query">The query builder.</param>
/// <param name="arguments">The paging arguments.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns></returns>
public ValueTask <CollectionSegment <TEntity> > ApplyPaginationAsync(
TQuery query,
OffsetPagingArguments arguments,
CancellationToken cancellationToken) =>
ApplyPaginationAsync(query, arguments, null, cancellationToken);
