EF Core Filtering

Question

I have something that currently looks like this and works in EF Core:

DbContext.Computers.OrderByDirection(state.SortDirection, 
    x => x.Actions.FirstOrDefault(y => y.GetType() == typeof(PingAction) && 
    y.History.Any(z => z.Status == Status.Succeeded && 
    (DateTime.Now - z.WhenExecuted).TotalMinutes < 10)))

However I also need to use the x function elsewhere and don't want to hard code it multiple times. How can I save that function to a variable or something and still allow it to work with the server sided filtering of EF core since of course this will be translated to SQL?

UPDATE

Signatures for OrderByDirection:

public static IOrderedEnumerable<TSource> OrderByDirection<TSource, TKey>(this IEnumerable<TSource> source, SortDirection direction, Func<TSource, TKey> keySelector)
public static IOrderedQueryable<TSource> OrderByDirection<TSource, TKey>(this IQueryable<TSource> source, SortDirection direction, Expression<Func<TSource, TKey>> keySelector)

Is OrderByDirection a custom extension method? You can probably save the function definition in an Expression and forward that to this method and use it elsewhere if you have to. learn.microsoft.com/en-us/dotnet/csharp/programming-guide/… — fbede
– fbede, Commented Feb 17, 2022 at 14:14
@fbede Ooops, didn't realise it but you're right, it belongs to MudBlazor which I'm using of course. — JohnUbuntu
– JohnUbuntu, Commented Feb 17, 2022 at 14:50
@fbede what would my expression look like and how would I pass it? — JohnUbuntu
– JohnUbuntu, Commented Feb 17, 2022 at 14:51
can you add the method header of OrderByDirection? Especially the parameter types. — fbede
– fbede, Commented Feb 17, 2022 at 15:10

fbede · Accepted Answer · 2022-02-18 16:33:24Z

1

I think you could extract the expression into a variable similarly to this:

(I am only guessing the class names by your property names, they aren't obvious from your code):

Expression<Func<Computer, Action>> expression = x => x.Actions.FirstOrDefault(
    action => action.GetType() == typeof(PingAction) && action.History.Any(
        history => history.Status == Status.Succeeded && (DateTime.Now - z.WhenExecuted).TotalMinutes < 10));

DbContext.Computers.OrderByDirection(state.SortDirection, expression);

then this expression can be reused elsewhere.

answered Feb 18, 2022 at 16:33

fbede

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