C#•2y ago

How to return a named predicates

Hi friends, I want to build a Method that returns a set of Predicates Example:

    private Predicate<Core.Entities.StudentAbsence>[] GetPredicates( SearchStudentAbsencesQuery query )
    {
        var whereFullNameContainsValue = new Predicate<Core.Entities.StudentAbsence>( x => ( x.StudentEnrollment.Student.FirstName + x.StudentEnrollment.Student.FamilyName ).Contains( query.Value ) );
        var whereSchoolSubjectTitleContainsValue = new Predicate<Core.Entities.StudentAbsence>( x => x.SchoolSubject.FullTitle.Contains( query.Value ) );
// Other predicates

        var predicates = new[]
                         {
                             whereFullNameContainsValue ,
                             whereSchoolSubjectTitleContainsValue ,
                             // Others
                         };
        
        return predicates;
    }

    private Predicate<Core.Entities.StudentAbsence>[] GetPredicates( SearchStudentAbsencesQuery query )
    {
        var whereFullNameContainsValue = new Predicate<Core.Entities.StudentAbsence>( x => ( x.StudentEnrollment.Student.FirstName + x.StudentEnrollment.Student.FamilyName ).Contains( query.Value ) );
        var whereSchoolSubjectTitleContainsValue = new Predicate<Core.Entities.StudentAbsence>( x => x.SchoolSubject.FullTitle.Contains( query.Value ) );
// Other predicates

        var predicates = new[]
                         {
                             whereFullNameContainsValue ,
                             whereSchoolSubjectTitleContainsValue ,
                             // Others
                         };
        
        return predicates;
    }

The Issue: How do I can return those predicates but everyone with a name like properties, let me explain more depending on the example I provided the use of that result will be like this:

var predicates = GetPredicates(Query);

var result = await db.<StudentAbsence>().Where( predicates[0] || predicates[1] //... ).ToListAsync()

var predicates = GetPredicates(Query);

var result = await db.<StudentAbsence>().Where( predicates[0] || predicates[1] //... ).ToListAsync()

as you will notice that to get every predicate I should use its index, instead of that I want when I got the predicates use their names like this following

var predicates = GetPredicates(Query);

var result = await db.<StudentAbsence>().Where( predicates.whereFullNameContainsValue  || predicates.whereSchoolSubjectTitleContainsValue //... ).ToListAsync()

var predicates = GetPredicates(Query);

var result = await db.<StudentAbsence>().Where( predicates.whereFullNameContainsValue  || predicates.whereSchoolSubjectTitleContainsValue //... ).ToListAsync()

I hope the explanation of the issue is clear, please is this even possible, if yes how do I can achieve this ? and massive thanks.

8 Replies

Becquerel•2y ago

you will want to make a class that contains properties with your desired names that provides access to these predicates or return a named tuple, but that's yucky

M B V R K•2y ago

hmmm, the problem is this method will works generically and the names of predicates will not be fixed

Becquerel•2y ago

then I think you're out of luck if you want to use names at compile time, you have to know the names at compile time

M B V R K•2y ago

hmmmm so this maybe impossible right ?

Becquerel•2y ago

unless i'm missing something, and you don't wanna make a new class, then yeah i think so

M B V R K•2y ago

this be done using Anonymous types ?

Becquerel•2y ago

possibly i don't mess around with those too much

phaseshift•2y ago

Make a class with normal properties (as already said), or return a dict and use string or enum as the key

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How to return a named predicates