如何使用 System.Linq.Async 中的 WhereAwait 和自定义布尔值

Question

I have a database and I make a lot of Where calls to it to make a table in Blazor. This takes long because Where is not Async. To speed this up I wanted to change the Where statements by using: ToAsyncEnumerable().WhereAwait from System.Linq.Async.

This is my line of code:

series5 = _context.ChickenSeries.ToAsyncEnumerable().WhereAwait(async serie => await ((serie.DatumWeek5 >= firstDay && serie.DatumWeek5 <= lastDay) && serie.SlaughterHouse.SlaughterHouseId != LeegstandID));

The error presenting on this line: 'bool' does not contain a definition for 'GetAwaiter'...

How do I resolve this issue?

Original post where code is based on: How can I use "Where" with an async predicate? The last answer.

Answer 1

Where is operator for filtering data and it is DO NOT EXECUTES query, it just defines filter for query. So no asyncs is needed for Where . You have to apply it on IQueryable to filter data.

Try to rewrite your query in the following way:

var result = await _context.ChickenSeries
    .Where(serie => (serie.DatumWeek5 >= firstDay && serie.DatumWeek5 <= lastDay) && serie.SlaughterHouse.SlaughterHouseId != LeegstandID)
    .ToListAsync();

If it is still slow, there are options:

1. Number of returned records is too high
2. Database has no proper indexes and you have to analyze SQL Server execution plan.