ersatztv/ErsatzTV.Application/MediaCollections/Queries/GetPagedRerunCollectionsHandler.cs

using ErsatzTV.Core.Domain;
using ErsatzTV.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using static ErsatzTV.Application.MediaCollections.Mapper;

namespace ErsatzTV.Application.MediaCollections;

public class GetPagedRerunCollectionsHandler(IDbContextFactory<TvContext> dbContextFactory)
    : IRequestHandler<GetPagedRerunCollections, PagedRerunCollectionsViewModel>
{
    public async Task<PagedRerunCollectionsViewModel> Handle(
        GetPagedRerunCollections request,
        CancellationToken cancellationToken)
    {
        await using TvContext dbContext = await dbContextFactory.CreateDbContextAsync(cancellationToken);
        IQueryable<RerunCollection> query = dbContext.RerunCollections.AsNoTracking();

        if (!string.IsNullOrWhiteSpace(request.Query))
        {
            query = query.Where(rc => EF.Functions.Like(rc.Name, $"%{request.Query}%"));
        }

        // count the SAME query the page is taken from, so the two cannot drift (issues #690, #758).
        // The includes belong to the page chain only — a COUNT does not materialize the graph.
        int count = await query.CountAsync(cancellationToken);

        // EF applies the includes to the paged subquery, so the selection graph is loaded for at most
        // PageSize rows — the per-request cost is bounded by the page, not by the table (issue #671).
        List<RerunCollectionViewModel> page = await query
            .IncludeSelectionDetails()
            .OrderBy(rc => rc.Name)
            .Skip(request.PageNum * request.PageSize)
            .Take(request.PageSize)
            .ToListAsync(cancellationToken)
            .Map(list => list.Map(ProjectToViewModel).ToList());

        return new PagedRerunCollectionsViewModel(count, page);
    }
}