entity framework core - Extension method not applying LINQ where clause

Question

I'm trying to implement Query objects into my code, but have encountered a problem. When passing meetId = 1 to GetMeetingDTO an exception is thrown by SingleOrDefault(). My Database currently holds 6 meetings all with unique Ids (1-6). I have checked if values are passed correctly via FilterOptions to FilterMeetingsBy and I looks ok (using Visual Studio). Apparrently no filtering is applied thus SingleOrDefault throws the error. I have tested leaving out the extension method and applying .Where(p => p.Id == 1) directly on the context. Then no error is thrown...

    public async Task<MeetingDTO> GetMeetingDTO(long meetId)
    {
        IEnumerable<Meeting> meetings = await context.MeetDbSet
            .FilterMeetingsBy(new FilterOptions { MeetingId = meetId }).ToListAsync();

        return mapper.Map<MeetingDTO>(meetings.SingleOrDefault());
    }

Here is the extension method

public static class FilterMeetings
{
    public static IQueryable<Meeting> FilterMeetingsBy(this IQueryable<Meeting> meetings, FilterOptions options)
    {
        if (options == null)
            return meetings;

        if (options.MeetingId.HasValue)
        {
            meetings.Where(p => p.Id == options.MeetingId.Value);
            return meetings;
        }

        if (options.SortFromDate.HasValue)
            meetings.Where(p => p.StartDate >= options.SortFromDate.Value);
        if (options.SortToDate.HasValue)
            meetings.Where(p => p.StartDate <= options.SortToDate.Value);

        return meetings;
    }
}

public class FilterOptions
{
    public long? MeetingId { get; set; }

    public DateTime? SortFromDate { get; set; }
    public DateTime? SortToDate { get; set; }
}

question from:https://stackoverflow.com/questions/65887386/extension-method-not-applying-linq-where-clause

Answer 1

The extension method returns the original query. LINQ operators don't modify the original query, they return a new query. The extension method doesn't return the new query though.

It should be rewritten to :

public static IQueryable<Meeting> FilterMeetingsBy(
        this IQueryable<Meeting> query, 
        FilterOptions options)
{
    if (options == null)
        return query;

    if (options.MeetingId.HasValue)
    {
        query =query.Where(p => p.Id == options.MeetingId.Value);
        return query;
    }

    if (options.SortFromDate.HasValue)
    {
        query=query.Where(p => p.StartDate >= options.SortFromDate.Value);
    }
    if (options.SortToDate.HasValue)
    {
        query=query.Where(p => p.StartDate <= options.SortToDate.Value);
    }

    return query;
}