Frustration with lookup columns

[WhatDidDavidDo]

Each time I've tried to create a canvas app, I get held up on this type of issue and cannot proceed.

I'm uploading an ERD for context. 

I have the code below in a dropdown OnChange so that it filters to the appropriate students based on the selected class. My ultimate goal is to populate a gallery with the StudentNames.

Set(SelectedClass, DropdownClass.Selected);

ClearCollect(

    FilteredEnrollments,

    AddColumns(

        Filter(Enrollments, ClassID.ClassID = SelectedClass.ClassID),

        StudentName,

        LookUp(Students, StudentID = StudentID).StudentFirstName & " " & LookUp(Students, StudentID = StudentID).StudentLastName

    )

)

Currently, it incorrectly shows the same student name for each item in the gallery (see Screenshot1 - StudentID). Just for fun, I added a second column to Enrollments called StudentID2 (not a lookup like StudentID is, but a copy of the same values). When I change the code to use StudentID2 instead of StudentID, it works as intended (see Screenshot2 - StudentID2). Therefore, it is having trouble using the original StudentID lookup column.

[WhatDidDavidDo]

I appreciate your persistence. I tried that and it does not pull any names. See attached screenshot.

[venturemavenwil]

Then the records are not being cascading, possibly because the Dataverse table itself is too large. Can we try to do an experiment?

AddColumns(
    Filter(
        ShowColumns(
            Enrollments, 
            EnrollmentID, ClassID, StudentIDe
        ),
        ClassID.ClassID = SelectedClass.ClassID
    ),
    StudentName,
    StudentIDe.StudentFirstName & " " & StudentIDe.StudentLastName
)

See if the Names populate now. 

[WhatDidDavidDo]

I can't get your test to run. It wasn't recognizing the ClassID.ClassID nor the ClassID after SelectedClass.

I went ahead and renamed Enrollments.ClassID to ClassIDe and Class.ClassID to ClassIDc to help know what we're working with.

Therefore I updated my original code to this:

Set(SelectedClass, DropdownClass.Selected);
ClearCollect(
    FilteredEnrollments,
    AddColumns(
        Filter(Enrollments, ClassIDe.ClassIDc = SelectedClass.ClassIDc),
        StudentName,
        StudentIDe.StudentFirstName & " " & StudentIDe.StudentLastName
    )
)

But when I change your test code to different combinations of ClassIDe and ClassIDc it still doesn't recognize. I'm even less familiar with showing columns as I am with adding columns.

Also, none of my tables are very large. The Enrollments is the largest with 40 rows and just the few columns.

[venturemavenwil · Accepted solution]

Sorry for the confusion. The code is supposed to just be used as an example since I don't know the logical names of your fields. 

I suspect the real code would look more like this

AddColumns(
    Filter(
        ShowColumns(
            Enrollments, 
            EnrollmentID, ClassID, StudentIDe
        ),
        crff0_classid.ClassID = SelectedClass.ClassID
    ),
    StudentName,
    crff0_studentid.StudentFirstName & " " & crff0_studentid.StudentLastName
)

After you use ShowColumns, Canvas App's auto suggest should tell you what the "real" name of the columns are. The idea is to limit the number of columns to what you need on the page. 

[WhatDidDavidDo]

That last code you gave me worked! Thank you!

Set(SelectedClass, DropdownClass.Selected);
ClearCollect(
    FilteredEnrollments,
    AddColumns(
    Filter(
        ShowColumns(
            Enrollments, 
            EnrollmentID, ClassIDe, StudentIDe
        ),
        crff0_ClassID.ClassIDc = SelectedClass.ClassIDc
    ),
    StudentName,
    crff0_StudentID.StudentFirstName & " " & crff0_StudentID.StudentLastName
)
)